assignment operators golang

Go Tutorial

Go exercises, go assignment operators, assignment operators.

Assignment operators are used to assign values to variables.

In the example below, we use the assignment operator ( = ) to assign the value 10 to a variable called x :

The addition assignment operator ( += ) adds a value to a variable:

A list of all assignment operators:

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Golang := Vs = Exploring Assignment Operators In Go

Explore the nuances of Go's := and = operators. This article breaks down their uses, scope considerations, and best practices, helping you write clearer, more efficient Go code.

In Go, understanding the distinction between the ':=' and '=' operators is crucial for efficient coding. The ':=' operator is used for declaring and initializing a new variable, while '=' is for assigning a value to an existing variable. This nuanced difference can significantly impact the functionality and efficiency of your Go programs.

Understanding := (Short Variable Declaration)

Understanding = (assignment operator), when to use := vs =, scope considerations, type inference with :=, common pitfalls and how to avoid them, best practices, frequently asked questions.

Short variable declaration , designated by := , is a concise way to declare and initialize a variable in Go. This operator allows you to create a variable with a type inferred from the right-hand side of the expression.

For instance, consider the following code snippet:

Here, name and age are declared and initialized without explicitly stating their types ( string and int , respectively).

When To Use Short Variable Declaration

Limitations and scope.

The := operator is particularly useful in local scopes , such as within functions or blocks, where brevity and efficiency are key. It's a go-to choice for assigning initial values to variables that will be used within a limited scope .

Consider a function:

count is declared and initialized within the function's scope, making the code cleaner and more readable.

While := is convenient, it has limitations. It cannot be used for global variable declarations. Also, it's designed for declaring new variables . If you try to redeclare an already declared variable in the same scope using := , the compiler will throw an error.

For example:

In summary, := is a powerful feature in Go for efficient variable declaration and initialization, with a focus on type inference and local scope usage. Use it to write cleaner, more concise code in functions and blocks.

The assignment operator , = , in Go, is used to assign values to already declared variables. Unlike := , it does not declare a new variable but modifies the value of an existing one.

Here, age is first declared as an integer, and then 30 is assigned to it using = .

Reassignment And Existing Variables

Global and local scope.

One of the key uses of = is to reassign values to variables. This is crucial in scenarios where the value of a variable changes over time within the same scope.

In this case, count is initially 10, but is later changed to 20.

The = operator works in both global and local scopes . It is versatile and can be used anywhere in your code, provided the variable it's being assigned to has been declared.

In this snippet, globalVar is assigned a value within a function, while localVar is assigned within its local scope.

Remember, = does not infer type. The variable's type must be clear either from its declaration or context. This operator is essential for variable value management throughout your Go programs, offering flexibility in variable usage and value updates.

Understanding the Problem:

Here is the relevant code snippet:

Here's the modified code:

Choosing between := and = in Go depends on the context and the specific requirements of the code. It's crucial to understand their appropriate use cases to write efficient and error-free programs.

New Variable Declaration

Existing variable assignment, reassigning and declaring variables.

Use := when you need to declare and initialize a new variable within a local scope. This operator is a shorthand that infers the variable's type based on the value assigned.

In this example, name is a new variable declared and initialized within the function.

Use = when you are working with already declared variables . This operator is used to update or change the value of the variable.

Here, count is an existing variable, and its value is being updated.

:= is limited to local scopes , such as inside functions or blocks. It cannot be used for global variable declarations. Conversely, = can be used in both local and global scopes.

It's important to distinguish situations where you are reassigning a value to an existing variable and when you are declaring a new one. Misusing := and = can lead to compile-time errors.

In summary, := is for declaring new variables with type inference, primarily in local scopes, while = is for assigning or updating values in both local and global scopes. Proper usage of these operators is key to writing clean and efficient Go code.

Understanding the scope of variables in Go is critical when deciding between := and = . The scope determines where a variable can be accessed or modified within the program.

Local Scope And :=

Global scope and =, redeclaration and shadowing, choosing the right scope.

The := operator is restricted to local scope . It's typically used within functions or blocks to declare and initialize variables that are not needed outside of that specific context.

Here, localVariable is accessible only within the example function.

Variables declared outside of any function, in the global scope , can be accessed and modified using the = operator from anywhere in the program.

globalVariable can be accessed and modified in any function.

In Go, shadowing can occur if a local variable is declared with the same name as a global variable. This is a common issue when using := in a local scope.

In the function example , num is a new local variable, different from the global num .

It's important to choose the right scope for your variables. Use global variables sparingly, as they can lead to code that is harder to debug and maintain. Prefer local scope with := for variables that don't need to be accessed globally.

Understanding and managing scope effectively ensures that your Go programs are more maintainable, less prone to errors, and easier to understand. Proper scope management using := and = is a key aspect of effective Go programming.

Type inference is a powerful feature of Go's := operator. It allows the compiler to automatically determine the type of the variable based on the value assigned to it.

Automatic Type Deduction

Mixed type declarations, limitations of type inference, practical use in functions.

When you use := , you do not need to explicitly declare the data type of the variable. This makes the code more concise and easier to write, especially in complex functions or when dealing with multiple variables.

In these examples, the types ( string for name and int for age ) are inferred automatically.

Type inference with := also works when declaring multiple variables in a single line, each possibly having a different type.

Here, name and age are declared in one line with different inferred types.

While type inference is convenient, it is important to be aware of its limitations . The type is inferred at the time of declaration and cannot be changed later.

In this case, attempting to assign a string to balance , initially inferred as float64 , results in an error.

Type inference is particularly useful in functions, especially when dealing with return values of different types or working with complex data structures.

Here, value 's type is inferred from the return type of someCalculation .

Type inference with := simplifies variable declaration and makes Go code more readable and easier to maintain. It's a feature that, when used appropriately, can greatly enhance the efficiency of your coding process in Go.

When using := and = , there are several common pitfalls that Go programmers may encounter. Being aware of these and knowing how to avoid them is crucial for writing effective code.

Re-declaration In The Same Scope

Shadowing global variables, incorrect type inference, accidental global declarations, using = without prior declaration.

One common mistake is attempting to re-declare a variable in the same scope using := . This results in a compilation error.

To avoid this, use = for reassignment within the same scope.

Shadowing occurs when a local variable with the same name as a global variable is declared. This can lead to unexpected behavior.

To avoid shadowing, choose distinct names for local variables or explicitly use the global variable.

Another pitfall is incorrect type inference , where the inferred type is not what the programmer expected.

Always ensure the initial value accurately represents the desired type.

Using := outside of a function accidentally creates a new local variable in the global scope, which may lead to unused variables or compilation errors.

To modify a global variable, use = within functions.

Trying to use = without a prior declaration of the variable will result in an error. Ensure that the variable is declared before using = for assignment.

Declare the variable first or use := if declaring a new variable.

Avoiding these pitfalls involves careful consideration of the scope, understanding the nuances of := and = , and ensuring proper variable declarations. By being mindful of these aspects, programmers can effectively utilize both operators in Go.

Adopting best practices when using := and = in Go can significantly enhance the readability and maintainability of your code.

Clear And Concise Declarations

Minimizing global variables, consistent use of operators, avoiding unnecessary shadowing, type checking and initialization.

Use := for local variable declarations where type inference makes the code more concise. This not only saves space but also enhances readability.

This approach makes the function more readable and straightforward.

Limit the use of global variables . When necessary, use = to assign values to them and be cautious of accidental shadowing in local scopes.

Careful management of global variables helps in maintaining a clear code structure.

Be consistent in your use of := and = . Consistency aids in understanding the flow of variable declarations and assignments throughout your code.

Avoid shadowing unless intentionally used as part of the program logic. Use distinct names for local variables to prevent confusion.

Using distinct names enhances the clarity of the code.

Use := when you want to declare and initialize a variable in one line, and when the type is clear from the context. Ensure the initial value represents the desired type accurately.

This practice ensures that the type and intent of the variable are clear.

By following these best practices, you can effectively leverage the strengths of both := and = in Go, leading to code that is efficient, clear, and easy to maintain.

What distinguishes the capacity and length of a slice in Go?

In Go, a slice's capacity (cap) refers to the total number of elements the underlying array can hold, while its length (len) indicates the current number of elements in the slice. Slices are dynamic, resizing the array automatically when needed. The capacity increases as elements are appended beyond its initial limit, leading to a new, larger underlying array.

How can I stop VS Code from showing a warning about needing comments for my exported 'Agent' struct in Go?

To resolve the linter warning for your exported 'Agent' type in Go, add a comment starting with the type's name. For instance:

go // Agent represents... type Agent struct { name string categoryId int }

This warning occurs because Go's documentation generator, godoc, uses comments for auto-generating documentation. If you prefer not to export the type, declare it in lowercase:

go type agent struct { name string categoryId int }

You can find examples of documented Go projects on pkg.go.dev. If you upload your Go project to GitHub, pkg.go.dev can automatically generate its documentation using these comments. You can also include runnable code examples and more, as seen in go-doc tricks.

What is the difference between using *float64 and sql.NullFloat64 in Golang ORM for fields like latitude and longitude in a struct?

Russ Cox explains that there's no significant difference between using float64 and sql.NullFloat64. Both work fine, but sql.Null structs might express the intent more clearly. Using a pointer could give the garbage collector more to track. In debugging, sql.Null* structs display more readable values compared to pointers. Therefore, he recommends using sql.Null* structs.

Why doesn't auto-completion work for GO in VS Code with WSL terminal, despite having GO-related extensions installed?

Try enabling Go's Language Server (gopls) in VS Code settings. After enabling, restart VS Code. You may need to install or update gopls and other tools. Be aware that gopls is still in beta, so it may crash or use excessive CPU, but improvements are ongoing.

Let's see what you learned!

In Go, when should you use the := operator instead of the = operator?

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Go Tutorial
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Go - Environment Setup
Go - Program Structure
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Go - Variables
Go - Constants
Go - Operators
Go - Decision Making
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Computer Glossary

Go - Assignment Operators

The following table lists all the assignment operators supported by Go language −

Try the following example to understand all the assignment operators available in Go programming language −

When you compile and execute the above program it produces the following result −

Go Operators

Go Type Casting

Go Flow Control

Go Boolean Expression
Go if...else
Go for Loop
Go while Loop
Go break and continue

Go Data Structures

Go Functions
Go Variable Scope
Go Recursion
Go Anonymous Function
Go Packages

Go Pointers & Interface

Go Pointers

Go Pointers and Functions
Go Pointers to Struct
Go Interface
Go Empty Interface
Go Type Assertions

Go Additional Topics

Go defer, panic, and recover

Go Tutorials

Go Booleans (Relational and Logical Operators)

Go Pointers to Structs

In Computer Programming, an operator is a symbol that performs operations on a value or a variable.

For example, + is an operator that is used to add two numbers.

Go programming provides wide range of operators that are categorized into following major categories:

Arithmetic operators
Assignment operator
Relational operators
Logical operators
Arithmetic Operator

We use arithmetic operators to perform arithmetic operations like addition, subtraction, multiplication, and division.

Here's a list of various arithmetic operators available in Go.

Example 1: Addition, Subtraction and Multiplication Operators

Example 2: golang division operator.

In the above example, we have used the / operator to divide two numbers: 11 and 4 . Here, we get the output 2 .

However, in normal calculation, 11 / 4 gives 2.75 . This is because when we use the / operator with integer values, we get the quotients instead of the actual result.

The division operator with integer values returns the quotient.

If we want the actual result we should always use the / operator with floating point numbers. For example,

Here, we get the actual result after division.

Example 3: Modulus Operator in Go

In the above example, we have used the modulo operator with numbers: 11 and 4 . Here, we get the result 3 .

This is because in programming, the modulo operator always returns the remainder after division.

The modulo operator in golang returns the remainder after division.

Note: The modulo operator is always used with integer values.

Increment and Decrement Operator in Go

In Golang, we use ++ (increment) and -- (decrement) operators to increase and decrease the value of a variable by 1 respectively. For example,

In the above example,

num++ - increases the value of num by 1 , from 5 to 6
num-- - decreases the value of num by 1 , from 5 to 4

Note: We have used ++ and -- as prefixes (before variable). However, we can also use them as postfixes ( num++ and num-- ).

There is a slight difference between using increment and decrement operators as prefixes and postfixes. To learn the difference, visit Increment and Decrement Operator as Prefix and Postfix .

Go Assignment Operators

We use the assignment operator to assign values to a variable. For example,

Here, the = operator assigns the value on right ( 34 ) to the variable on left ( number ).

Example: Assignment Operator in Go

In the above example, we have used the assignment operator to assign the value of the num variable to the result variable.

Compound Assignment Operators

In Go, we can also use an assignment operator together with an arithmetic operator. For example,

Here, += is additional assignment operator. It first adds 6 to the value of number ( 2 ) and assigns the final result ( 8 ) to number .

Here's a list of various compound assignment operators available in Golang.

Relational Operators in Golang

We use the relational operators to compare two values or variables. For example,

Here, == is a relational operator that checks if 5 is equal to 6 .

A relational operator returns

true if the comparison between two values is correct
false if the comparison is wrong

Here's a list of various relational operators available in Go:

To learn more, visit Go relational operators .

Logical Operators in Go

We use the logical operators to perform logical operations. A logical operator returns either true or false depending upon the conditions.

To learn more, visit Go logical operators .

Go Assignment Operators

What are assignment operators.

Assignment operators are used to assign variables to values.

The Assignment Operator ( = )

The equal sign that we are all familiar with is called the assignment operator, because it is the most important out of all the assignment operators. All the other assignment operators are built off of it. For example, the below code assigns the variable a the value of 3, the constant pi the value of 3.14, and the variable website the value of Learnmonkey:

Notice that we can use the assignment operator to make constants and variables. We can also use the assignment operator to set variables (not constants) once they are already created:

Other Assignment Operators

The other assignment operators were created so that as developers, our lives would be easier. They are all equivalent to using the assignment operator in some way:

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Posted on May 7, 2022 • Originally published at mr-destructive.github.io

Golang: Operators

Introduction.

In this 13th part of the series, we will be exploring the fundamentals of operators in Golang. We will be exploring the basics of operators and the various types like Arithmetic, Bitwise, Comparison, Assignment operators in Golang.

Operators are quite fundamentals in any programming language. Operators are basically expressions or a set of character(s) to perform certain fundamental tasks. They allow us to perform certain trivial operations with a simple expression or character. There are quite a few operators in Golang to perform various operations.

Types of Operators

Golang has a few types of operators, each type providing particular aspect of forming expressions and evaluate conditions.

Bitwise Operators

Logical operators, arithmetic operators, assignment operators, comparison operators.

Bitwise Operators are used in performing operations on binary numbers. We can perform operation on a bit level and hence they are known as bitwise operators. Some fundamental bitwise operators include, AND , OR , NOT , and EXOR . Using this operators, the bits in the operands can be manipulated and certain logical operations can be performed.

We use the & (AND operator) for performing AND operations on two operands. Here we are logically ANDing 3 and 5 i.e. 011 with 101 so it becomes 001 in binary or 1 in decimal.

Also, the | (OR operator) for performing logical OR operation on two operands. Here we are logically ORing 3 and 5 i.e. 011 with 101 so it becomes 111 in binary or 7 in decimal.

Also the ^ (EXOR operator) for performing logical EXOR operation on two operands. Here we are logically EXORing 3 and 5 i.e. 011 with 101 so it becomes 110 in binary or 6 in decimal.

We have a couple of more bitwise operators that allow us to shift bits in the binary representation of the number. We have two types of these shift operators, right sift and left shift operators. The main function of these operator is to shift a bit in either right or left direction.

In the above example, we have shifted 3 i.e. 011 to right by one bit so it becomes 001 . If we would have given x >> 2 it would have become 0 since the last bit was shifted to right and hence all bits were 0.

Similarly, the left shift operator sifts the bits in the binary representation of the number to the left. So, in the example above, 5 i.e. 101 is shifted left by one bit so it becomes 1010 in binary i.e. 10 in decimal.

This was a basic overview of bitwise operators in Golang. We can use these basic operators to perform low level operations on numbers.

This type of operators are quite important and widely used as they form the fundamentals of comparison of variables and forming boolean expressions. The comparison operator is used to compare two values or expressions.

We use simple comparison operators like == or != for comparing if two values are equal or not. The expression a == b will evaluate to true if the values of both variables or operands are equal. However, the expression a != b will evaluate to true if the values of both variables or operands are not equal.

Similarly, we have the < and > operators which allow us to evaluate expression by comparing if the values are less than or grater than the other operand. So, the expression a > b will evaluate to true if the value of a is greater than the value of b . Also the expression a < b will evaluate to true if the value of a is less than the value of b .

Finally, the operators <= and >= allow us to evaluate expression by comparing if the values are less than or equal to and greater than or equal to the other operand. So, the expression a >= b will evaluate to true if the value of a is greater than or if it is equal to the value of b , else it would evaluate to false . Similarly, the expression a <= b will evaluate to true if the value of a is less than or if it is equal to the value of b , else it would evaluate to false .

These was a basic overview of comparison operators in golang.

Next, we move on to the logical operators in Golang which allow to perform logical operations like AND , OR , and NOT with conditional statements or storing boolean expressions.

Here, we have used logical operators like && for Logical AND, || for logical OR, and ! for complementing the evaluated result. The && operation only evaluates to true if both the expressions are true and || OR operator evaluates to true if either or both the expressions are true . The ! operator is used to complement the evaluated expression from the preceding parenthesis.

Arithmetic operators are used for performing Arithmetic operations. We have few basic arithmetic operators like + , - , * , / , and % for adding, subtracting, multiplication, division, and modulus operation in golang.

These are the basic mathematical operators in any programming language. We can use + to add two values, - to subtract two values, * to multiply to values, / for division of two values and finally % to get the remainder of a division of two values i.e. if we divide 30 by 50, the remainder is 30 and the quotient is 0.

We also have a few other operators like ++ and -- that help in incrementing and decrementing values by a unit value. Let's say we have a variable k which is set to 4 and we want to increment it by one, so we can definitely use k = k + 1 but it looks kind of too long, we have a short notation for the same k++ to do the same.

So, we can see that the variable k is incremented by one and variable j is decremented by 1 using the ++ and -- operator.

These types of operators are quite handy and can condense down large operations into simple expressions. These types of operators allow us to perform operation on the same operand. Let's say we have the variable k set to 20 initially, we want to add 30 to the variable k , we can do that by using k = k + 30 but a more sophisticated way would be to use k += 30 which adds 30 or any value provided the same variable assigned and operated on.

From the above example, we are able to perform operations by using shorthand notations like += to add the value to the same operand. These also saves a bit of time and memory not much but considerable enough. This allow us to directly access and modify the contents of the provided operand in the register rather than assigning different registers and performing the operations.

That's it from this part. Reference for all the code examples and commands can be found in the 100 days of Golang GitHub repository.

So, from the following part of the series, we were able to learn the basics of operators in golang. Using some simple and easy to understand examples, we were able to explore different types of operators like arithmetic, logical, assignment and bitwise operators in golang. These are quite fundamental in programming in general, this lays a good foundation for working with larger and complex projects that deal with any kind of logic in it, without a doubt almost all of the applications do have a bit of logic attached to it. So, we need to know the basics of operators in golang.

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Go operators

last modified August 24, 2023

In this article we cover Go operators. We show how to use operators to create expressions.

We use Go version 1.18.

An operator is a special symbol which indicates a certain process is carried out. Operators in programming languages are taken from mathematics. Programmers work with data. The operators are used to process data. An operand is one of the inputs (arguments) of an operator.

Expressions are constructed from operands and operators. The operators of an expression indicate which operations to apply to the operands. The order of evaluation of operators in an expression is determined by the precedence and associativity of the operators.

An operator usually has one or two operands. Those operators that work with only one operand are called unary operators . Those who work with two operands are called binary operators .

Certain operators may be used in different contexts. For instance the + operator can be used in different cases: it adds numbers, concatenates strings, or indicates the sign of a number. We say that the operator is overloaded .

Go sign operators

There are two sign operators: + and - . They are used to indicate or change the sign of a value.

The + and - signs indicate the sign of a value. The plus sign can be used to signal that we have a positive number. It can be omitted and it is in most cases done so.

The minus sign changes the sign of a value.

Go assignment operator

The assignment operator = assigns a value to a variable. A variable is a placeholder for a value. In mathematics, the = operator has a different meaning. In an equation, the = operator is an equality operator. The left side of the equation is equal to the right one.

Here we assign a number to the x variable.

This expression does not make sense in mathematics, but it is legal in programming. The expression adds 1 to the x variable. The right side is equal to 2 and 2 is assigned to x .

This code line leads to a syntax error. We cannot assign a value to a literal.

Go has a short variable declaration operator := ; it declares a variable and assigns a value in one step. The x := 2 is equal to var x = 2 .

Go increment and decrement operators

We often increment or decrement a value by one in programming. Go has two convenient operators for this: ++ and -- .

In the above example, we demonstrate the usage of both operators.

We initiate the x variable to 6. Then we increment x two times. Now the variable equals to 8.

We use the decrement operator. Now the variable equals to 7.

Go compound assignment operators

The compound assignment operators consist of two operators. They are shorthand operators.

The += compound operator is one of these shorthand operators. The above two expressions are equal. Value 3 is added to the a variable.

Other compound operators include:

In the code example, we use two compound operators.

The a variable is initiated to one. 1 is added to the variable using the non-shorthand notation.

Using a += compound operator, we add 5 to the a variable. The statement is equal to a = a + 5 .

Using the *= operator, the a is multiplied by 3. The statement is equal to a = a * 3 .

Go arithmetic operators

The following is a table of arithmetic operators in Go.

The following example shows arithmetic operations.

In the preceding example, we use addition, subtraction, multiplication, division, and remainder operations. This is all familiar from the mathematics.

The % operator is called the remainder or the modulo operator. It finds the remainder of division of one number by another. For example, 9 % 4 , 9 modulo 4 is 1, because 4 goes into 9 twice with a remainder of 1.

Next we will show the distinction between integer and floating point division.

In the preceding example, we divide two numbers.

In this code, we have done integer division. The returned value of the division operation is an integer. When we divide two integers the result is an integer.

If one of the values is a double or a float, we perform a floating point division. In our case, the second operand is a double so the result is a double.

Go Boolean operators

In Go we have three logical operators.

Boolean operators are also called logical.

Many expressions result in a boolean value. For instance, boolean values are used in conditional statements.

Relational operators always result in a boolean value. These two lines print false and true.

The body of the if statement is executed only if the condition inside the parentheses is met. The y > x returns true, so the message "y is greater than x" is printed to the terminal.

The true and false keywords represent boolean literals in Go.

The code example shows the logical and (&&) operator. It evaluates to true only if both operands are true.

Only one expression results in true.

The logical or ( || ) operator evaluates to true if either of the operands is true.

If one of the sides of the operator is true, the outcome of the operation is true.

Three of four expressions result in true.

The negation operator ! makes true false and false true.

The example shows the negation operator in action.

Go comparison operators

Comparison operators are used to compare values. These operators always result in a boolean value.

comparison operators are also called relational operators.

In the code example, we have four expressions. These expressions compare integer values. The result of each of the expressions is either true or false. In Go we use the == to compare numbers. (Some languages like Ada, Visual Basic, or Pascal use = for comparing numbers.)

Go bitwise operators

Decimal numbers are natural to humans. Binary numbers are native to computers. Binary, octal, decimal, or hexadecimal symbols are only notations of the same number. Bitwise operators work with bits of a binary number.

The bitwise and operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 only if both corresponding bits in the operands are 1.

The first number is a binary notation of 6, the second is 3, and the result is 2.

The bitwise or operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 if either of the corresponding bits in the operands is 1.

The result is 00110 or decimal 7.

The bitwise exclusive or operator performs bit-by-bit comparison between two numbers. The result for a bit position is 1 if one or the other (but not both) of the corresponding bits in the operands is 1.

The result is 00101 or decimal 5.

Go pointer operators

In Go, the & is an address of operator and the * is a pointer indirection operator.

In the code example, we demonstrate the two operators.

An integer variable is defined.

We get the address of the count variable; we create a pointer to the variable.

Via the pointer dereference, we modify the value of count.

Again, via pointer dereference, we print the value to which the pointer refers.

Go channel operator

A channels is a typed conduit through which we can send and receive values with the channel operator <- .

The example presents the channel operator.

We send a value to the channel.

We receive a value from the channel.

Go operator precedence

The operator precedence tells us which operators are evaluated first. The precedence level is necessary to avoid ambiguity in expressions.

What is the outcome of the following expression, 28 or 40?

Like in mathematics, the multiplication operator has a higher precedence than addition operator. So the outcome is 28.

To change the order of evaluation, we can use parentheses. Expressions inside parentheses are always evaluated first. The result of the above expression is 40.

In this code example, we show a few expressions. The outcome of each expression is dependent on the precedence level.

This line prints 28. The multiplication operator has a higher precedence than addition. First, the product of 5 * 5 is calculated, then 3 is added.

The evaluation of the expression can be altered by using round brackets. In this case, the 3 + 5 is evaluated and later the value is multiplied by 5. This line prints 40.

In this case, the negation operator has a higher precedence than the bitwise or. First, the initial true value is negated to false, then the | operator combines false and true, which gives true in the end.

Associativity rule

Sometimes the precedence is not satisfactory to determine the outcome of an expression. There is another rule called associativity . The associativity of operators determines the order of evaluation of operators with the same precedence level.

What is the outcome of this expression, 9 or 1? The multiplication, deletion, and the modulo operator are left to right associated. So the expression is evaluated this way: (9 / 3) * 3 and the result is 9.

Arithmetic, boolean and relational operators are left to right associated. The ternary operator, increment, decrement, unary plus and minus, negation, bitwise not, type cast, object creation operators are right to left associated.

In the code example, we the associativity rule determines the outcome of the expression.

The compound assignment operators are right to left associated. We might expect the result to be 1. But the actual result is 0. Because of the associativity. The expression on the right is evaluated first and then the compound assignment operator is applied.

In this article we have covered Go operators.

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

List all Go tutorials .

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Golang reference, beego framework, golang operators.

An operator is a symbol that tells the compiler to perform certain actions. The following lists describe the different operators used in Golang.

Arithmetic Operators
Assignment Operators
Comparison Operators
Logical Operators
Bitwise Operators

Arithmetic Operators in Go Programming Language

The arithmetic operators are used to perform common arithmetical operations, such as addition, subtraction, multiplication etc.

Here's a complete list of Golang's arithmetic operators:

The following example will show you these arithmetic operators in action:

Assignment Operators in Go Programming Language

The assignment operators are used to assign values to variables

The following example will show you these assignment operators in action:

Comparison Operators in Go Programming Language

Comparison operators are used to compare two values.

The following example will show you these comparison operators in action:

Logical Operators in Go Programming Language

Logical operators are used to determine the logic between variables or values.

The following example will show you these logical operators in action:

Bitwise Operators in Go Programming Language

Bitwise operators are used to compare (binary) numbers.

The following example will show you these bitwise operators in action:

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Operators are the foundation of any programming language. Thus the functionality of the Go language is incomplete without the use of operators. Operators allow us to perform different kinds of operations on operands. In the Go language , operators Can be categorized based on their different functionality:

Arithmetic Operators

Relational operators, logical operators, bitwise operators, assignment operators, misc operators.

These are used to perform arithmetic/mathematical operations on operands in Go language:

Addition: The ‘+’ operator adds two operands. For example, x+y.
Subtraction: The ‘-‘ operator subtracts two operands. For example, x-y.
Multiplication: The ‘*’ operator multiplies two operands. For example, x*y.
Division: The ‘/’ operator divides the first operand by the second. For example, x/y.
Modulus: The ‘%’ operator returns the remainder when the first operand is divided by the second. For example, x%y.

Note: -, +, !, &, *, <-, and ^ are also known as unary operators and the precedence of unary operators is higher. ++ and — operators are from statements they are not expressions, so they are out from the operator hierarchy.

Example:

Output:

Relational operators are used for the comparison of two values. Let’s see them one by one:

‘=='(Equal To) operator checks whether the two given operands are equal or not. If so, it returns true. Otherwise, it returns false. For example, 5==5 will return true.
‘!='(Not Equal To) operator checks whether the two given operands are equal or not. If not, it returns true. Otherwise, it returns false. It is the exact boolean complement of the ‘==’ operator. For example, 5!=5 will return false.
‘>'(Greater Than) operator checks whether the first operand is greater than the second operand. If so, it returns true. Otherwise, it returns false. For example, 6>5 will return true.
‘<‘(Less Than) operator checks whether the first operand is lesser than the second operand. If so, it returns true. Otherwise, it returns false. For example, 6<5 will return false.
‘>='(Greater Than Equal To) operator checks whether the first operand is greater than or equal to the second operand. If so, it returns true. Otherwise, it returns false. For example, 5>=5 will return true.
‘<='(Less Than Equal To) operator checks whether the first operand is lesser than or equal to the second operand. If so, it returns true. Otherwise, it returns false. For example, 5<=5 will also return true.

They are used to combine two or more conditions/constraints or to complement the evaluation of the original condition in consideration.

Logical AND: The ‘&&’ operator returns true when both the conditions in consideration are satisfied. Otherwise it returns false. For example, a && b returns true when both a and b are true (i.e. non-zero).
Logical OR: The ‘||’ operator returns true when one (or both) of the conditions in consideration is satisfied. Otherwise it returns false. For example, a || b returns true if one of a or b is true (i.e. non-zero). Of course, it returns true when both a and b are true.
Logical NOT: The ‘!’ operator returns true the condition in consideration is not satisfied. Otherwise it returns false. For example, !a returns true if a is false, i.e. when a=0.

In Go language, there are 6 bitwise operators which work at bit level or used to perform bit by bit operations. Following are the bitwise operators :

& (bitwise AND): Takes two numbers as operands and does AND on every bit of two numbers. The result of AND is 1 only if both bits are 1.
| (bitwise OR): Takes two numbers as operands and does OR on every bit of two numbers. The result of OR is 1 any of the two bits is 1.
^ (bitwise XOR): Takes two numbers as operands and does XOR on every bit of two numbers. The result of XOR is 1 if the two bits are different.
<< (left shift): Takes two numbers, left shifts the bits of the first operand, the second operand decides the number of places to shift.
>> (right shift): Takes two numbers, right shifts the bits of the first operand, the second operand decides the number of places to shift.
&^ (AND NOT): This is a bit clear operator.

Assignment operators are used to assigning a value to a variable. The left side operand of the assignment operator is a variable and right side operand of the assignment operator is a value. The value on the right side must be of the same data-type of the variable on the left side otherwise the compiler will raise an error. Different types of assignment operators are shown below:

“=”(Simple Assignment): This is the simplest assignment operator. This operator is used to assign the value on the right to the variable on the left.
“+=”(Add Assignment): This operator is a combination of ‘+’ and ‘=’ operators. This operator first adds the current value of the variable on left to the value on the right and then assigns the result to the variable on the left.
“-=”(Subtract Assignment): This operator is a combination of ‘-‘ and ‘=’ operators. This operator first subtracts the current value of the variable on left from the value on the right and then assigns the result to the variable on the left.
“*=”(Multiply Assignment): This operator is a combination of ‘*’ and ‘=’ operators. This operator first multiplies the current value of the variable on left to the value on the right and then assigns the result to the variable on the left.
“/=”(Division Assignment): This operator is a combination of ‘/’ and ‘=’ operators. This operator first divides the current value of the variable on left by the value on the right and then assigns the result to the variable on the left.
“%=”(Modulus Assignment): This operator is a combination of ‘%’ and ‘=’ operators. This operator first modulo the current value of the variable on left by the value on the right and then assigns the result to the variable on the left.
“&=”(Bitwise AND Assignment): This operator is a combination of ‘&’ and ‘=’ operators. This operator first “Bitwise AND” the current value of the variable on the left by the value on the right and then assigns the result to the variable on the left.
“^=”(Bitwise Exclusive OR): This operator is a combination of ‘^’ and ‘=’ operators. This operator first “Bitwise Exclusive OR” the current value of the variable on left by the value on the right and then assigns the result to the variable on the left.
“|=”(Bitwise Inclusive OR): This operator is a combination of ‘|’ and ‘=’ operators. This operator first “Bitwise Inclusive OR” the current value of the variable on left by the value on the right and then assigns the result to the variable on the left.
“<<=”(Left shift AND assignment operator): This operator is a combination of ‘<<’ and ‘=’ operators. This operator first “Left shift AND” the current value of the variable on left by the value on the right and then assigns the result to the variable on the left.
“>>=”(Right shift AND assignment operator): This operator is a combination of ‘>>’ and ‘=’ operators. This operator first “Right shift AND” the current value of the variable on left by the value on the right and then assigns the result to the variable on the left.
&: This operator returns the address of the variable.
*: This operator provides pointer to a variable.
<-: The name of this operator is receive. It is used to receive a value from the channel.

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Go Operators

Operators are symbols that allow us to perform various mathematical and logical operations on values and variables.

In Go, operators can be classified as below:

Arithmetic Operators

The arithmetic operators can be used in the basic arithmetic operations on literal values or variables.

The following example demonstrates arithmetic operations such as addition, subtraction, and modulus.

Comparison Operators

Comparison operators are used to compare two literal values or variables.

The following example demonstrates comparisons operators.

Logical Operators:

The logical operators are used to perform logical operations by combining two or more conditions. They return either true or false depending upon the conditions.

The following example demonstrates the logical operators.

Bitwise Operators

The bitwise operators work on bits and perform bit-by-bit operation.

The following example demonstrates the bitwise operations.

In the above example, two int variables are x = 3 and y = 5 . Binary of 3 is 0011 and 5 is 0101. so, x & y is 0001, which is numeric 1. x | y is 0111 which is numeric 7, and x ^ y is 0110 which is numeric 6.

Assignment Operators

The assignment operators are used to assign literal values or assign values by performing some arithmetic operation using arithmetic operators.

The following example demonstrates the assignment operators.

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Home » Golang

Golang Assignment Operators

Here, we are going to learn about the Assignment Operators in the Go programming language with examples. Submitted by IncludeHelp , on December 08, 2021

Assignment Operators

Assignment operators are used for assigning the expressions or values to the variable/ constant etc. These operators assign the result of the right-side expression to the left-side variable or constant. The " = " is an assignment operator. Assignment operators can also be the combinations of some other operators (+, -, *, /, %, etc.) and " = ". Such operators are known as compound assignment operators .

List of Golang Assignment Operators

Example of golang assignment operators.

The below Golang program is demonstrating the example of assignment operators.

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Learn Golang Operators Guide with examples

Dec 31, 2023

# Go Language Operators

Like many programming languages, Golang has support for various inbuilt operators.

Important keynotes of operators in the Go language

Operators are character sequences used to execute some operations on a given operand(s)
Each operator in the Go language is of types Unary Operator or Binary Operator. Binary operators accept two operands, Unary Operator accepts one operand
Operators operate on one or two operands with expressions
These are used to form expressions

The following are different types covered as part of this blog post.

Arithmetic Operators
Relational Operators
Logical Operators
Bitwise Operators
Assignment Operator
Address Operators
Other Operators
Operator Precedence

Operators syntax :

There are two types of operators

unary - applies to the single operand
binary - applies to two operands.

Here is a Unary Operator Syntax

Here is a Binary Operator Syntax

The operand is data or variables that need to be manipulated.

# Golang Arithmetic Operators

Arithmetic operators perform arithmetic calculations like addition, multiplication, subtract, on numeric values. Assume that Operands a and b values are 10,5.

Four operators (+,-,*,/) operate on Numeric types such as Integer and Float , Complex . + operator on String. ++ and -- operators on Numeric types.

Following is an example for the usage of Arithmetic operators

The output of the above program code execution is

# Golang Comparison or Relational Operators

Comparison operators are used to compare the operands in an expression. Operands can be named type and compared operand of same type or values of the same type.

These operators enclosed in ( and ) i.e (a==b) , If it is not enclosed - a == b gives compilation error - cannot use a == b (type bool) as type int in assignment Operands of any type as mentioned in below keynotes. And returned value of this comparison is untyped a boolean value - true or false.

Keynotes of Comparison Operators

All primitive types (Integers, Floats, Boolean, String) are comparable
Complex data types, Channel Pointer can be used to compare with these
Interfaces can be comparable and return true - if both interfaces are of the same dynamic type, values, or nil, else return false
if Structs can be comparable and returns true - properties or fields are equal
if arrays compared with this, returns true - if both array values are equal

Following are a list of Go Inbuilt Comparison Operators

Below is a Golang comparison operators example

When the above program is compiled and executed outputs the below results

# Golang Logical Operators

Logical operators accept the Boolean value and return a Boolean value.

It contains Left and Right Operands. If Left Operand is evaluated to true, Right Operand will not be evaluated.

These are called short circuit rules, if both operands (1 && 1)are not Boolean, and gives compilation error invalid operation: 1 && 1 (operator && not defined on untyped number)

Following is a list of operators supported in the Go language.

Here is an example of Logical Operator usage

Compilation and running of the above is

# Golang Bitwise Operators

These operators are used with bit manipulation. Go language has supported different bitwise operators. It operates on bits only. Generate true table manipulation values on bits 0 and 1

Following is a List of Bitwise Operators supported in Go

Here is an example for Logical Operator example

# Golang Assignment Operators

Assignment operators are used to perform the calculation of some operations and finally result is assigned to the left side operand.

Golang has support for multiple assignment operators

Following is an example of Using assignment Operators

When the above program code is compiled and executed, Output is

# Golang Address Operators

There are two operators related address of a variable asterisk * Operator These are used to give a pointer of a variable and dereference pointer which gives a pointer to a point of points.

Ampersand & Operator This gives the address of a variable. It gives the actual location of the variable saved in memory. Here is an example of Asterisk and Ampersand Operator

The output of the above programs is

# Golang Operator Precedence

In any expression, multiple operators are applied, Precedence decides the evaluation order on which operators run first. Unary Operators rank the highest precedence than binary operators. You can check official documentation [here] https://golang.org/ref/spec 🔗 .

The Go Programming Language Specification

Version of jul 26, 2021, introduction.

This is a reference manual for the Go programming language. For more information and other documents, see golang.org .

Go is a general-purpose language designed with systems programming in mind. It is strongly typed and garbage-collected and has explicit support for concurrent programming. Programs are constructed from packages , whose properties allow efficient management of dependencies.

The grammar is compact and simple to parse, allowing for easy analysis by automatic tools such as integrated development environments.

The syntax is specified using Extended Backus-Naur Form (EBNF):

Productions are expressions constructed from terms and the following operators, in increasing precedence:

Lower-case production names are used to identify lexical tokens. Non-terminals are in CamelCase. Lexical tokens are enclosed in double quotes "" or back quotes `` .

The form a … b represents the set of characters from a through b as alternatives. The horizontal ellipsis … is also used elsewhere in the spec to informally denote various enumerations or code snippets that are not further specified. The character … (as opposed to the three characters ... ) is not a token of the Go language.

Source code representation

Source code is Unicode text encoded in UTF-8 . The text is not canonicalized, so a single accented code point is distinct from the same character constructed from combining an accent and a letter; those are treated as two code points. For simplicity, this document will use the unqualified term character to refer to a Unicode code point in the source text.

Each code point is distinct; for instance, upper and lower case letters are different characters.

Implementation restriction: For compatibility with other tools, a compiler may disallow the NUL character (U+0000) in the source text.

Implementation restriction: For compatibility with other tools, a compiler may ignore a UTF-8-encoded byte order mark (U+FEFF) if it is the first Unicode code point in the source text. A byte order mark may be disallowed anywhere else in the source.

The following terms are used to denote specific Unicode character classes:

In The Unicode Standard 8.0 , Section 4.5 "General Category" defines a set of character categories. Go treats all characters in any of the Letter categories Lu, Ll, Lt, Lm, or Lo as Unicode letters, and those in the Number category Nd as Unicode digits.

Letters and digits

The underscore character _ (U+005F) is considered a letter.

Lexical elements

Comments serve as program documentation. There are two forms:

Line comments start with the character sequence // and stop at the end of the line.
General comments start with the character sequence /* and stop with the first subsequent character sequence */ .

A comment cannot start inside a rune or string literal , or inside a comment. A general comment containing no newlines acts like a space. Any other comment acts like a newline.

Tokens form the vocabulary of the Go language. There are four classes: identifiers , keywords , operators and punctuation , and literals . White space , formed from spaces (U+0020), horizontal tabs (U+0009), carriage returns (U+000D), and newlines (U+000A), is ignored except as it separates tokens that would otherwise combine into a single token. Also, a newline or end of file may trigger the insertion of a semicolon . While breaking the input into tokens, the next token is the longest sequence of characters that form a valid token.

The formal grammar uses semicolons ";" as terminators in a number of productions. Go programs may omit most of these semicolons using the following two rules:

an identifier
an integer , floating-point , imaginary , rune , or string literal
one of the keywords break , continue , fallthrough , or return
one of the operators and punctuation ++ , -- , ) , ] , or }
To allow complex statements to occupy a single line, a semicolon may be omitted before a closing ")" or "}" .

To reflect idiomatic use, code examples in this document elide semicolons using these rules.

Identifiers

Identifiers name program entities such as variables and types. An identifier is a sequence of one or more letters and digits. The first character in an identifier must be a letter.

Some identifiers are predeclared .

The following keywords are reserved and may not be used as identifiers.

Operators and punctuation

The following character sequences represent operators (including assignment operators ) and punctuation:

Integer literals

An integer literal is a sequence of digits representing an integer constant . An optional prefix sets a non-decimal base: 0b or 0B for binary, 0 , 0o , or 0O for octal, and 0x or 0X for hexadecimal. A single 0 is considered a decimal zero. In hexadecimal literals, letters a through f and A through F represent values 10 through 15.

For readability, an underscore character _ may appear after a base prefix or between successive digits; such underscores do not change the literal's value.

Floating-point literals

A floating-point literal is a decimal or hexadecimal representation of a floating-point constant .

A decimal floating-point literal consists of an integer part (decimal digits), a decimal point, a fractional part (decimal digits), and an exponent part ( e or E followed by an optional sign and decimal digits). One of the integer part or the fractional part may be elided; one of the decimal point or the exponent part may be elided. An exponent value exp scales the mantissa (integer and fractional part) by 10 exp .

A hexadecimal floating-point literal consists of a 0x or 0X prefix, an integer part (hexadecimal digits), a radix point, a fractional part (hexadecimal digits), and an exponent part ( p or P followed by an optional sign and decimal digits). One of the integer part or the fractional part may be elided; the radix point may be elided as well, but the exponent part is required. (This syntax matches the one given in IEEE 754-2008 §5.12.3.) An exponent value exp scales the mantissa (integer and fractional part) by 2 exp .

For readability, an underscore character _ may appear after a base prefix or between successive digits; such underscores do not change the literal value.

Imaginary literals

An imaginary literal represents the imaginary part of a complex constant . It consists of an integer or floating-point literal followed by the lower-case letter i . The value of an imaginary literal is the value of the respective integer or floating-point literal multiplied by the imaginary unit i .

For backward compatibility, an imaginary literal's integer part consisting entirely of decimal digits (and possibly underscores) is considered a decimal integer, even if it starts with a leading 0 .

Rune literals

A rune literal represents a rune constant , an integer value identifying a Unicode code point. A rune literal is expressed as one or more characters enclosed in single quotes, as in 'x' or '\n' . Within the quotes, any character may appear except newline and unescaped single quote. A single quoted character represents the Unicode value of the character itself, while multi-character sequences beginning with a backslash encode values in various formats.

The simplest form represents the single character within the quotes; since Go source text is Unicode characters encoded in UTF-8, multiple UTF-8-encoded bytes may represent a single integer value. For instance, the literal 'a' holds a single byte representing a literal a , Unicode U+0061, value 0x61 , while 'ä' holds two bytes ( 0xc3 0xa4 ) representing a literal a -dieresis, U+00E4, value 0xe4 .

Several backslash escapes allow arbitrary values to be encoded as ASCII text. There are four ways to represent the integer value as a numeric constant: \x followed by exactly two hexadecimal digits; \u followed by exactly four hexadecimal digits; \U followed by exactly eight hexadecimal digits, and a plain backslash \ followed by exactly three octal digits. In each case the value of the literal is the value represented by the digits in the corresponding base.

Although these representations all result in an integer, they have different valid ranges. Octal escapes must represent a value between 0 and 255 inclusive. Hexadecimal escapes satisfy this condition by construction. The escapes \u and \U represent Unicode code points so within them some values are illegal, in particular those above 0x10FFFF and surrogate halves.

After a backslash, certain single-character escapes represent special values:

All other sequences starting with a backslash are illegal inside rune literals.

String literals

A string literal represents a string constant obtained from concatenating a sequence of characters. There are two forms: raw string literals and interpreted string literals.

Raw string literals are character sequences between back quotes, as in `foo` . Within the quotes, any character may appear except back quote. The value of a raw string literal is the string composed of the uninterpreted (implicitly UTF-8-encoded) characters between the quotes; in particular, backslashes have no special meaning and the string may contain newlines. Carriage return characters ('\r') inside raw string literals are discarded from the raw string value.

Interpreted string literals are character sequences between double quotes, as in "bar" . Within the quotes, any character may appear except newline and unescaped double quote. The text between the quotes forms the value of the literal, with backslash escapes interpreted as they are in rune literals (except that \' is illegal and \" is legal), with the same restrictions. The three-digit octal ( \ nnn ) and two-digit hexadecimal ( \x nn ) escapes represent individual bytes of the resulting string; all other escapes represent the (possibly multi-byte) UTF-8 encoding of individual characters . Thus inside a string literal \377 and \xFF represent a single byte of value 0xFF =255, while ÿ , \u00FF , \U000000FF and \xc3\xbf represent the two bytes 0xc3 0xbf of the UTF-8 encoding of character U+00FF.

These examples all represent the same string:

If the source code represents a character as two code points, such as a combining form involving an accent and a letter, the result will be an error if placed in a rune literal (it is not a single code point), and will appear as two code points if placed in a string literal.

There are boolean constants , rune constants , integer constants , floating-point constants , complex constants , and string constants . Rune, integer, floating-point, and complex constants are collectively called numeric constants .

A constant value is represented by a rune , integer , floating-point , imaginary , or string literal, an identifier denoting a constant, a constant expression , a conversion with a result that is a constant, or the result value of some built-in functions such as unsafe.Sizeof applied to any value, cap or len applied to some expressions , real and imag applied to a complex constant and complex applied to numeric constants. The boolean truth values are represented by the predeclared constants true and false . The predeclared identifier iota denotes an integer constant.

In general, complex constants are a form of constant expression and are discussed in that section.

Numeric constants represent exact values of arbitrary precision and do not overflow. Consequently, there are no constants denoting the IEEE-754 negative zero, infinity, and not-a-number values.

Constants may be typed or untyped . Literal constants, true , false , iota , and certain constant expressions containing only untyped constant operands are untyped.

A constant may be given a type explicitly by a constant declaration or conversion , or implicitly when used in a variable declaration or an assignment or as an operand in an expression . It is an error if the constant value cannot be represented as a value of the respective type.

An untyped constant has a default type which is the type to which the constant is implicitly converted in contexts where a typed value is required, for instance, in a short variable declaration such as i := 0 where there is no explicit type. The default type of an untyped constant is bool , rune , int , float64 , complex128 or string respectively, depending on whether it is a boolean, rune, integer, floating-point, complex, or string constant.

Implementation restriction: Although numeric constants have arbitrary precision in the language, a compiler may implement them using an internal representation with limited precision. That said, every implementation must:

Represent integer constants with at least 256 bits.
Represent floating-point constants, including the parts of a complex constant, with a mantissa of at least 256 bits and a signed binary exponent of at least 16 bits.
Give an error if unable to represent an integer constant precisely.
Give an error if unable to represent a floating-point or complex constant due to overflow.
Round to the nearest representable constant if unable to represent a floating-point or complex constant due to limits on precision.

These requirements apply both to literal constants and to the result of evaluating constant expressions .

A variable is a storage location for holding a value . The set of permissible values is determined by the variable's type .

A variable declaration or, for function parameters and results, the signature of a function declaration or function literal reserves storage for a named variable. Calling the built-in function new or taking the address of a composite literal allocates storage for a variable at run time. Such an anonymous variable is referred to via a (possibly implicit) pointer indirection .

Structured variables of array , slice , and struct types have elements and fields that may be addressed individually. Each such element acts like a variable.

The static type (or just type ) of a variable is the type given in its declaration, the type provided in the new call or composite literal, or the type of an element of a structured variable. Variables of interface type also have a distinct dynamic type , which is the concrete type of the value assigned to the variable at run time (unless the value is the predeclared identifier nil , which has no type). The dynamic type may vary during execution but values stored in interface variables are always assignable to the static type of the variable.

A variable's value is retrieved by referring to the variable in an expression ; it is the most recent value assigned to the variable. If a variable has not yet been assigned a value, its value is the zero value for its type.

A type determines a set of values together with operations and methods specific to those values. A type may be denoted by a type name , if it has one, or specified using a type literal , which composes a type from existing types.

The language predeclares certain type names. Others are introduced with type declarations . Composite types —array, struct, pointer, function, interface, slice, map, and channel types—may be constructed using type literals.

Each type T has an underlying type : If T is one of the predeclared boolean, numeric, or string types, or a type literal, the corresponding underlying type is T itself. Otherwise, T 's underlying type is the underlying type of the type to which T refers in its type declaration .

The underlying type of string , A1 , A2 , B1 , and B2 is string . The underlying type of []B1 , B3 , and B4 is []B1 .

Method sets

A type has a (possibly empty) method set associated with it. The method set of an interface type is its interface. The method set of any other type T consists of all methods declared with receiver type T . The method set of the corresponding pointer type *T is the set of all methods declared with receiver *T or T (that is, it also contains the method set of T ). Further rules apply to structs containing embedded fields, as described in the section on struct types . Any other type has an empty method set. In a method set, each method must have a unique non- blank method name .

The method set of a type determines the interfaces that the type implements and the methods that can be called using a receiver of that type.

Boolean types

A boolean type represents the set of Boolean truth values denoted by the predeclared constants true and false . The predeclared boolean type is bool ; it is a defined type .

Numeric types

A numeric type represents sets of integer or floating-point values. The predeclared architecture-independent numeric types are:

The value of an n -bit integer is n bits wide and represented using two's complement arithmetic .

There is also a set of predeclared numeric types with implementation-specific sizes:

String types

A string type represents the set of string values. A string value is a (possibly empty) sequence of bytes. The number of bytes is called the length of the string and is never negative. Strings are immutable: once created, it is impossible to change the contents of a string. The predeclared string type is string ; it is a defined type .

The length of a string s can be discovered using the built-in function len . The length is a compile-time constant if the string is a constant. A string's bytes can be accessed by integer indices 0 through len(s)-1 . It is illegal to take the address of such an element; if s[i] is the i 'th byte of a string, &s[i] is invalid.

Array types

An array is a numbered sequence of elements of a single type, called the element type. The number of elements is called the length of the array and is never negative.

The length is part of the array's type; it must evaluate to a non-negative constant representable by a value of type int . The length of array a can be discovered using the built-in function len . The elements can be addressed by integer indices 0 through len(a)-1 . Array types are always one-dimensional but may be composed to form multi-dimensional types.

Slice types

A slice is a descriptor for a contiguous segment of an underlying array and provides access to a numbered sequence of elements from that array. A slice type denotes the set of all slices of arrays of its element type. The number of elements is called the length of the slice and is never negative. The value of an uninitialized slice is nil .

The length of a slice s can be discovered by the built-in function len ; unlike with arrays it may change during execution. The elements can be addressed by integer indices 0 through len(s)-1 . The slice index of a given element may be less than the index of the same element in the underlying array.

A slice, once initialized, is always associated with an underlying array that holds its elements. A slice therefore shares storage with its array and with other slices of the same array; by contrast, distinct arrays always represent distinct storage.

The array underlying a slice may extend past the end of the slice. The capacity is a measure of that extent: it is the sum of the length of the slice and the length of the array beyond the slice; a slice of length up to that capacity can be created by slicing a new one from the original slice. The capacity of a slice a can be discovered using the built-in function cap(a) .

A new, initialized slice value for a given element type T is made using the built-in function make , which takes a slice type and parameters specifying the length and optionally the capacity. A slice created with make always allocates a new, hidden array to which the returned slice value refers. That is, executing

produces the same slice as allocating an array and slicing it, so these two expressions are equivalent:

Like arrays, slices are always one-dimensional but may be composed to construct higher-dimensional objects. With arrays of arrays, the inner arrays are, by construction, always the same length; however with slices of slices (or arrays of slices), the inner lengths may vary dynamically. Moreover, the inner slices must be initialized individually.

Struct types

A struct is a sequence of named elements, called fields, each of which has a name and a type. Field names may be specified explicitly (IdentifierList) or implicitly (EmbeddedField). Within a struct, non- blank field names must be unique .

A field declared with a type but no explicit field name is called an embedded field . An embedded field must be specified as a type name T or as a pointer to a non-interface type name *T , and T itself may not be a pointer type. The unqualified type name acts as the field name.

The following declaration is illegal because field names must be unique in a struct type:

A field or method f of an embedded field in a struct x is called promoted if x.f is a legal selector that denotes that field or method f .

Promoted fields act like ordinary fields of a struct except that they cannot be used as field names in composite literals of the struct.

Given a struct type S and a defined type T , promoted methods are included in the method set of the struct as follows:

If S contains an embedded field T , the method sets of S and *S both include promoted methods with receiver T . The method set of *S also includes promoted methods with receiver *T .
If S contains an embedded field *T , the method sets of S and *S both include promoted methods with receiver T or *T .

A field declaration may be followed by an optional string literal tag , which becomes an attribute for all the fields in the corresponding field declaration. An empty tag string is equivalent to an absent tag. The tags are made visible through a reflection interface and take part in type identity for structs but are otherwise ignored.

Pointer types

A pointer type denotes the set of all pointers to variables of a given type, called the base type of the pointer. The value of an uninitialized pointer is nil .

Function types

A function type denotes the set of all functions with the same parameter and result types. The value of an uninitialized variable of function type is nil .

Within a list of parameters or results, the names (IdentifierList) must either all be present or all be absent. If present, each name stands for one item (parameter or result) of the specified type and all non- blank names in the signature must be unique . If absent, each type stands for one item of that type. Parameter and result lists are always parenthesized except that if there is exactly one unnamed result it may be written as an unparenthesized type.

The final incoming parameter in a function signature may have a type prefixed with ... . A function with such a parameter is called variadic and may be invoked with zero or more arguments for that parameter.

Interface types

An interface type specifies a method set called its interface . A variable of interface type can store a value of any type with a method set that is any superset of the interface. Such a type is said to implement the interface . The value of an uninitialized variable of interface type is nil .

An interface type may specify methods explicitly through method specifications, or it may embed methods of other interfaces through interface type names.

The name of each explicitly specified method must be unique and not blank .

More than one type may implement an interface. For instance, if two types S1 and S2 have the method set

(where T stands for either S1 or S2 ) then the File interface is implemented by both S1 and S2 , regardless of what other methods S1 and S2 may have or share.

A type implements any interface comprising any subset of its methods and may therefore implement several distinct interfaces. For instance, all types implement the empty interface :

Similarly, consider this interface specification, which appears within a type declaration to define an interface called Locker :

If S1 and S2 also implement

they implement the Locker interface as well as the File interface.

An interface T may use a (possibly qualified) interface type name E in place of a method specification. This is called embedding interface E in T . The method set of T is the union of the method sets of T ’s explicitly declared methods and of T ’s embedded interfaces.

A union of method sets contains the (exported and non-exported) methods of each method set exactly once, and methods with the same names must have identical signatures.

An interface type T may not embed itself or any interface type that embeds T , recursively.

A map is an unordered group of elements of one type, called the element type, indexed by a set of unique keys of another type, called the key type. The value of an uninitialized map is nil .

The comparison operators == and != must be fully defined for operands of the key type; thus the key type must not be a function, map, or slice. If the key type is an interface type, these comparison operators must be defined for the dynamic key values; failure will cause a run-time panic .

The number of map elements is called its length. For a map m , it can be discovered using the built-in function len and may change during execution. Elements may be added during execution using assignments and retrieved with index expressions ; they may be removed with the delete built-in function.

A new, empty map value is made using the built-in function make , which takes the map type and an optional capacity hint as arguments:

Channel types

A channel provides a mechanism for concurrently executing functions to communicate by sending and receiving values of a specified element type. The value of an uninitialized channel is nil .

The optional <- operator specifies the channel direction , send or receive . If no direction is given, the channel is bidirectional . A channel may be constrained only to send or only to receive by assignment or explicit conversion .

The <- operator associates with the leftmost chan possible:

A new, initialized channel value can be made using the built-in function make , which takes the channel type and an optional capacity as arguments:

The capacity, in number of elements, sets the size of the buffer in the channel. If the capacity is zero or absent, the channel is unbuffered and communication succeeds only when both a sender and receiver are ready. Otherwise, the channel is buffered and communication succeeds without blocking if the buffer is not full (sends) or not empty (receives). A nil channel is never ready for communication.

A channel may be closed with the built-in function close . The multi-valued assignment form of the receive operator reports whether a received value was sent before the channel was closed.

A single channel may be used in send statements , receive operations , and calls to the built-in functions cap and len by any number of goroutines without further synchronization. Channels act as first-in-first-out queues. For example, if one goroutine sends values on a channel and a second goroutine receives them, the values are received in the order sent.

Properties of types and values

Type identity.

Two types are either identical or different .

A defined type is always different from any other type. Otherwise, two types are identical if their underlying type literals are structurally equivalent; that is, they have the same literal structure and corresponding components have identical types. In detail:

Two array types are identical if they have identical element types and the same array length.
Two slice types are identical if they have identical element types.
Two struct types are identical if they have the same sequence of fields, and if corresponding fields have the same names, and identical types, and identical tags. Non-exported field names from different packages are always different.
Two pointer types are identical if they have identical base types.
Two function types are identical if they have the same number of parameters and result values, corresponding parameter and result types are identical, and either both functions are variadic or neither is. Parameter and result names are not required to match.
Two interface types are identical if they have the same set of methods with the same names and identical function types. Non-exported method names from different packages are always different. The order of the methods is irrelevant.
Two map types are identical if they have identical key and element types.
Two channel types are identical if they have identical element types and the same direction.

Given the declarations

these types are identical:

B0 and B1 are different because they are new types created by distinct type definitions ; func(int, float64) *B0 and func(x int, y float64) *[]string are different because B0 is different from []string .

Assignability

A value x is assignable to a variable of type T (" x is assignable to T ") if one of the following conditions applies:

x 's type is identical to T .
x 's type V and T have identical underlying types and at least one of V or T is not a defined type.
T is an interface type and x implements T .
x is a bidirectional channel value, T is a channel type, x 's type V and T have identical element types, and at least one of V or T is not a defined type.
x is the predeclared identifier nil and T is a pointer, function, slice, map, channel, or interface type.
x is an untyped constant representable by a value of type T .

Representability

A constant x is representable by a value of type T if one of the following conditions applies:

x is in the set of values determined by T .
T is a floating-point type and x can be rounded to T 's precision without overflow. Rounding uses IEEE 754 round-to-even rules but with an IEEE negative zero further simplified to an unsigned zero. Note that constant values never result in an IEEE negative zero, NaN, or infinity.
T is a complex type, and x 's components real(x) and imag(x) are representable by values of T 's component type ( float32 or float64 ).

A block is a possibly empty sequence of declarations and statements within matching brace brackets.

In addition to explicit blocks in the source code, there are implicit blocks:

The universe block encompasses all Go source text.
Each package has a package block containing all Go source text for that package.
Each file has a file block containing all Go source text in that file.
Each "if" , "for" , and "switch" statement is considered to be in its own implicit block.
Each clause in a "switch" or "select" statement acts as an implicit block.

Blocks nest and influence scoping .

Declarations and scope

A declaration binds a non- blank identifier to a constant , type , variable , function , label , or package . Every identifier in a program must be declared. No identifier may be declared twice in the same block, and no identifier may be declared in both the file and package block.

The blank identifier may be used like any other identifier in a declaration, but it does not introduce a binding and thus is not declared. In the package block, the identifier init may only be used for init function declarations, and like the blank identifier it does not introduce a new binding.

The scope of a declared identifier is the extent of source text in which the identifier denotes the specified constant, type, variable, function, label, or package.

Go is lexically scoped using blocks :

The scope of a predeclared identifier is the universe block.
The scope of an identifier denoting a constant, type, variable, or function (but not method) declared at top level (outside any function) is the package block.
The scope of the package name of an imported package is the file block of the file containing the import declaration.
The scope of an identifier denoting a method receiver, function parameter, or result variable is the function body.
The scope of a constant or variable identifier declared inside a function begins at the end of the ConstSpec or VarSpec (ShortVarDecl for short variable declarations) and ends at the end of the innermost containing block.
The scope of a type identifier declared inside a function begins at the identifier in the TypeSpec and ends at the end of the innermost containing block.

An identifier declared in a block may be redeclared in an inner block. While the identifier of the inner declaration is in scope, it denotes the entity declared by the inner declaration.

The package clause is not a declaration; the package name does not appear in any scope. Its purpose is to identify the files belonging to the same package and to specify the default package name for import declarations.

Label scopes

Labels are declared by labeled statements and are used in the "break" , "continue" , and "goto" statements. It is illegal to define a label that is never used. In contrast to other identifiers, labels are not block scoped and do not conflict with identifiers that are not labels. The scope of a label is the body of the function in which it is declared and excludes the body of any nested function.

Blank identifier

The blank identifier is represented by the underscore character _ . It serves as an anonymous placeholder instead of a regular (non-blank) identifier and has special meaning in declarations , as an operand , and in assignments .

Predeclared identifiers

The following identifiers are implicitly declared in the universe block :

Exported identifiers

An identifier may be exported to permit access to it from another package. An identifier is exported if both:

the first character of the identifier's name is a Unicode upper case letter (Unicode class "Lu"); and
the identifier is declared in the package block or it is a field name or method name .

All other identifiers are not exported.

Uniqueness of identifiers

Given a set of identifiers, an identifier is called unique if it is different from every other in the set. Two identifiers are different if they are spelled differently, or if they appear in different packages and are not exported . Otherwise, they are the same.

Constant declarations

A constant declaration binds a list of identifiers (the names of the constants) to the values of a list of constant expressions . The number of identifiers must be equal to the number of expressions, and the n th identifier on the left is bound to the value of the n th expression on the right.

If the type is present, all constants take the type specified, and the expressions must be assignable to that type. If the type is omitted, the constants take the individual types of the corresponding expressions. If the expression values are untyped constants , the declared constants remain untyped and the constant identifiers denote the constant values. For instance, if the expression is a floating-point literal, the constant identifier denotes a floating-point constant, even if the literal's fractional part is zero.

Within a parenthesized const declaration list the expression list may be omitted from any but the first ConstSpec. Such an empty list is equivalent to the textual substitution of the first preceding non-empty expression list and its type if any. Omitting the list of expressions is therefore equivalent to repeating the previous list. The number of identifiers must be equal to the number of expressions in the previous list. Together with the iota constant generator this mechanism permits light-weight declaration of sequential values:

Within a constant declaration , the predeclared identifier iota represents successive untyped integer constants . Its value is the index of the respective ConstSpec in that constant declaration, starting at zero. It can be used to construct a set of related constants:

By definition, multiple uses of iota in the same ConstSpec all have the same value:

This last example exploits the implicit repetition of the last non-empty expression list.

Type declarations

A type declaration binds an identifier, the type name , to a type . Type declarations come in two forms: alias declarations and type definitions.

Alias declarations

An alias declaration binds an identifier to the given type.

Within the scope of the identifier, it serves as an alias for the type.

Type definitions

A type definition creates a new, distinct type with the same underlying type and operations as the given type, and binds an identifier to it.

The new type is called a defined type . It is different from any other type, including the type it is created from.

A defined type may have methods associated with it. It does not inherit any methods bound to the given type, but the method set of an interface type or of elements of a composite type remains unchanged:

Type definitions may be used to define different boolean, numeric, or string types and associate methods with them:

Variable declarations

A variable declaration creates one or more variables , binds corresponding identifiers to them, and gives each a type and an initial value.

If a list of expressions is given, the variables are initialized with the expressions following the rules for assignments . Otherwise, each variable is initialized to its zero value .

If a type is present, each variable is given that type. Otherwise, each variable is given the type of the corresponding initialization value in the assignment. If that value is an untyped constant, it is first implicitly converted to its default type ; if it is an untyped boolean value, it is first implicitly converted to type bool . The predeclared value nil cannot be used to initialize a variable with no explicit type.

Implementation restriction: A compiler may make it illegal to declare a variable inside a function body if the variable is never used.

Short variable declarations

A short variable declaration uses the syntax:

It is shorthand for a regular variable declaration with initializer expressions but no types:

Unlike regular variable declarations, a short variable declaration may redeclare variables provided they were originally declared earlier in the same block (or the parameter lists if the block is the function body) with the same type, and at least one of the non- blank variables is new. As a consequence, redeclaration can only appear in a multi-variable short declaration. Redeclaration does not introduce a new variable; it just assigns a new value to the original.

Short variable declarations may appear only inside functions. In some contexts such as the initializers for "if" , "for" , or "switch" statements, they can be used to declare local temporary variables.

Function declarations

A function declaration binds an identifier, the function name , to a function.

If the function's signature declares result parameters, the function body's statement list must end in a terminating statement .

A function declaration may omit the body. Such a declaration provides the signature for a function implemented outside Go, such as an assembly routine.

Method declarations

A method is a function with a receiver . A method declaration binds an identifier, the method name , to a method, and associates the method with the receiver's base type .

The receiver is specified via an extra parameter section preceding the method name. That parameter section must declare a single non-variadic parameter, the receiver. Its type must be a defined type T or a pointer to a defined type T . T is called the receiver base type . A receiver base type cannot be a pointer or interface type and it must be defined in the same package as the method. The method is said to be bound to its receiver base type and the method name is visible only within selectors for type T or *T .

A non- blank receiver identifier must be unique in the method signature. If the receiver's value is not referenced inside the body of the method, its identifier may be omitted in the declaration. The same applies in general to parameters of functions and methods.

For a base type, the non-blank names of methods bound to it must be unique. If the base type is a struct type , the non-blank method and field names must be distinct.

Given defined type Point , the declarations

bind the methods Length and Scale , with receiver type *Point , to the base type Point .

The type of a method is the type of a function with the receiver as first argument. For instance, the method Scale has type

However, a function declared this way is not a method.

Expressions

An expression specifies the computation of a value by applying operators and functions to operands.

Operands denote the elementary values in an expression. An operand may be a literal, a (possibly qualified ) non- blank identifier denoting a constant , variable , or function , or a parenthesized expression.

The blank identifier may appear as an operand only on the left-hand side of an assignment .

Qualified identifiers

A qualified identifier is an identifier qualified with a package name prefix. Both the package name and the identifier must not be blank .

A qualified identifier accesses an identifier in a different package, which must be imported . The identifier must be exported and declared in the package block of that package.

Composite literals

Composite literals construct values for structs, arrays, slices, and maps and create a new value each time they are evaluated. They consist of the type of the literal followed by a brace-bound list of elements. Each element may optionally be preceded by a corresponding key.

The LiteralType's underlying type must be a struct, array, slice, or map type (the grammar enforces this constraint except when the type is given as a TypeName). The types of the elements and keys must be assignable to the respective field, element, and key types of the literal type; there is no additional conversion. The key is interpreted as a field name for struct literals, an index for array and slice literals, and a key for map literals. For map literals, all elements must have a key. It is an error to specify multiple elements with the same field name or constant key value. For non-constant map keys, see the section on evaluation order .

For struct literals the following rules apply:

A key must be a field name declared in the struct type.
An element list that does not contain any keys must list an element for each struct field in the order in which the fields are declared.
If any element has a key, every element must have a key.
An element list that contains keys does not need to have an element for each struct field. Omitted fields get the zero value for that field.
A literal may omit the element list; such a literal evaluates to the zero value for its type.
It is an error to specify an element for a non-exported field of a struct belonging to a different package.

one may write

For array and slice literals the following rules apply:

Each element has an associated integer index marking its position in the array.
An element with a key uses the key as its index. The key must be a non-negative constant representable by a value of type int ; and if it is typed it must be of integer type.
An element without a key uses the previous element's index plus one. If the first element has no key, its index is zero.

Taking the address of a composite literal generates a pointer to a unique variable initialized with the literal's value.

Note that the zero value for a slice or map type is not the same as an initialized but empty value of the same type. Consequently, taking the address of an empty slice or map composite literal does not have the same effect as allocating a new slice or map value with new .

The length of an array literal is the length specified in the literal type. If fewer elements than the length are provided in the literal, the missing elements are set to the zero value for the array element type. It is an error to provide elements with index values outside the index range of the array. The notation ... specifies an array length equal to the maximum element index plus one.

A slice literal describes the entire underlying array literal. Thus the length and capacity of a slice literal are the maximum element index plus one. A slice literal has the form

and is shorthand for a slice operation applied to an array:

Within a composite literal of array, slice, or map type T , elements or map keys that are themselves composite literals may elide the respective literal type if it is identical to the element or key type of T . Similarly, elements or keys that are addresses of composite literals may elide the &T when the element or key type is *T .

A parsing ambiguity arises when a composite literal using the TypeName form of the LiteralType appears as an operand between the keyword and the opening brace of the block of an "if", "for", or "switch" statement, and the composite literal is not enclosed in parentheses, square brackets, or curly braces. In this rare case, the opening brace of the literal is erroneously parsed as the one introducing the block of statements. To resolve the ambiguity, the composite literal must appear within parentheses.

Examples of valid array, slice, and map literals:

Function literals

A function literal represents an anonymous function .

A function literal can be assigned to a variable or invoked directly.

Function literals are closures : they may refer to variables defined in a surrounding function. Those variables are then shared between the surrounding function and the function literal, and they survive as long as they are accessible.

Primary expressions

Primary expressions are the operands for unary and binary expressions.

For a primary expression x that is not a package name , the selector expression

denotes the field or method f of the value x (or sometimes *x ; see below). The identifier f is called the (field or method) selector ; it must not be the blank identifier . The type of the selector expression is the type of f . If x is a package name, see the section on qualified identifiers .

A selector f may denote a field or method f of a type T , or it may refer to a field or method f of a nested embedded field of T . The number of embedded fields traversed to reach f is called its depth in T . The depth of a field or method f declared in T is zero. The depth of a field or method f declared in an embedded field A in T is the depth of f in A plus one.

The following rules apply to selectors:

For a value x of type T or *T where T is not a pointer or interface type, x.f denotes the field or method at the shallowest depth in T where there is such an f . If there is not exactly one f with shallowest depth, the selector expression is illegal.
For a value x of type I where I is an interface type, x.f denotes the actual method with name f of the dynamic value of x . If there is no method with name f in the method set of I , the selector expression is illegal.
As an exception, if the type of x is a defined pointer type and (*x).f is a valid selector expression denoting a field (but not a method), x.f is shorthand for (*x).f .
In all other cases, x.f is illegal.
If x is of pointer type and has the value nil and x.f denotes a struct field, assigning to or evaluating x.f causes a run-time panic .
If x is of interface type and has the value nil , calling or evaluating the method x.f causes a run-time panic .

For example, given the declarations:

one may write:

but the following is invalid:

Method expressions

If M is in the method set of type T , T.M is a function that is callable as a regular function with the same arguments as M prefixed by an additional argument that is the receiver of the method.

Consider a struct type T with two methods, Mv , whose receiver is of type T , and Mp , whose receiver is of type *T .

The expression

yields a function equivalent to Mv but with an explicit receiver as its first argument; it has signature

That function may be called normally with an explicit receiver, so these five invocations are equivalent:

Similarly, the expression

yields a function value representing Mp with signature

For a method with a value receiver, one can derive a function with an explicit pointer receiver, so

yields a function value representing Mv with signature

Such a function indirects through the receiver to create a value to pass as the receiver to the underlying method; the method does not overwrite the value whose address is passed in the function call.

The final case, a value-receiver function for a pointer-receiver method, is illegal because pointer-receiver methods are not in the method set of the value type.

Function values derived from methods are called with function call syntax; the receiver is provided as the first argument to the call. That is, given f := T.Mv , f is invoked as f(t, 7) not t.f(7) . To construct a function that binds the receiver, use a function literal or method value .

It is legal to derive a function value from a method of an interface type. The resulting function takes an explicit receiver of that interface type.

Method values

If the expression x has static type T and M is in the method set of type T , x.M is called a method value . The method value x.M is a function value that is callable with the same arguments as a method call of x.M . The expression x is evaluated and saved during the evaluation of the method value; the saved copy is then used as the receiver in any calls, which may be executed later.

The type T may be an interface or non-interface type.

As in the discussion of method expressions above, consider a struct type T with two methods, Mv , whose receiver is of type T , and Mp , whose receiver is of type *T .

yields a function value of type

These two invocations are equivalent:

As with selectors , a reference to a non-interface method with a value receiver using a pointer will automatically dereference that pointer: pt.Mv is equivalent to (*pt).Mv .

As with method calls , a reference to a non-interface method with a pointer receiver using an addressable value will automatically take the address of that value: t.Mp is equivalent to (&t).Mp .

Although the examples above use non-interface types, it is also legal to create a method value from a value of interface type.

Index expressions

A primary expression of the form

denotes the element of the array, pointer to array, slice, string or map a indexed by x . The value x is called the index or map key , respectively. The following rules apply:

If a is not a map:

the index x must be of integer type or an untyped constant
a constant index must be non-negative and representable by a value of type int
a constant index that is untyped is given type int
the index x is in range if 0 <= x < len(a) , otherwise it is out of range

For a of array type A :

a constant index must be in range
if x is out of range at run time, a run-time panic occurs
a[x] is the array element at index x and the type of a[x] is the element type of A

For a of pointer to array type:

a[x] is shorthand for (*a)[x]

For a of slice type S :

a[x] is the slice element at index x and the type of a[x] is the element type of S

For a of string type :

a constant index must be in range if the string a is also constant
a[x] is the non-constant byte value at index x and the type of a[x] is byte
a[x] may not be assigned to

For a of map type M :

x 's type must be assignable to the key type of M
if the map contains an entry with key x , a[x] is the map element with key x and the type of a[x] is the element type of M
if the map is nil or does not contain such an entry, a[x] is the zero value for the element type of M

Otherwise a[x] is illegal.

An index expression on a map a of type map[K]V used in an assignment or initialization of the special form

yields an additional untyped boolean value. The value of ok is true if the key x is present in the map, and false otherwise.

Assigning to an element of a nil map causes a run-time panic .

Slice expressions

Slice expressions construct a substring or slice from a string, array, pointer to array, or slice. There are two variants: a simple form that specifies a low and high bound, and a full form that also specifies a bound on the capacity.

Simple slice expressions

For a string, array, pointer to array, or slice a , the primary expression

constructs a substring or slice. The indices low and high select which elements of operand a appear in the result. The result has indices starting at 0 and length equal to high - low . After slicing the array a

the slice s has type []int , length 3, capacity 4, and elements

For convenience, any of the indices may be omitted. A missing low index defaults to zero; a missing high index defaults to the length of the sliced operand:

If a is a pointer to an array, a[low : high] is shorthand for (*a)[low : high] .

For arrays or strings, the indices are in range if 0 <= low <= high <= len(a) , otherwise they are out of range . For slices, the upper index bound is the slice capacity cap(a) rather than the length. A constant index must be non-negative and representable by a value of type int ; for arrays or constant strings, constant indices must also be in range. If both indices are constant, they must satisfy low <= high . If the indices are out of range at run time, a run-time panic occurs.

Except for untyped strings , if the sliced operand is a string or slice, the result of the slice operation is a non-constant value of the same type as the operand. For untyped string operands the result is a non-constant value of type string . If the sliced operand is an array, it must be addressable and the result of the slice operation is a slice with the same element type as the array.

If the sliced operand of a valid slice expression is a nil slice, the result is a nil slice. Otherwise, if the result is a slice, it shares its underlying array with the operand.

Full slice expressions

For an array, pointer to array, or slice a (but not a string), the primary expression

constructs a slice of the same type, and with the same length and elements as the simple slice expression a[low : high] . Additionally, it controls the resulting slice's capacity by setting it to max - low . Only the first index may be omitted; it defaults to 0. After slicing the array a

the slice t has type []int , length 2, capacity 4, and elements

As for simple slice expressions, if a is a pointer to an array, a[low : high : max] is shorthand for (*a)[low : high : max] . If the sliced operand is an array, it must be addressable .

The indices are in range if 0 <= low <= high <= max <= cap(a) , otherwise they are out of range . A constant index must be non-negative and representable by a value of type int ; for arrays, constant indices must also be in range. If multiple indices are constant, the constants that are present must be in range relative to each other. If the indices are out of range at run time, a run-time panic occurs.

Type assertions

For an expression x of interface type and a type T , the primary expression

asserts that x is not nil and that the value stored in x is of type T . The notation x.(T) is called a type assertion .

More precisely, if T is not an interface type, x.(T) asserts that the dynamic type of x is identical to the type T . In this case, T must implement the (interface) type of x ; otherwise the type assertion is invalid since it is not possible for x to store a value of type T . If T is an interface type, x.(T) asserts that the dynamic type of x implements the interface T .

If the type assertion holds, the value of the expression is the value stored in x and its type is T . If the type assertion is false, a run-time panic occurs. In other words, even though the dynamic type of x is known only at run time, the type of x.(T) is known to be T in a correct program.

A type assertion used in an assignment or initialization of the special form

yields an additional untyped boolean value. The value of ok is true if the assertion holds. Otherwise it is false and the value of v is the zero value for type T . No run-time panic occurs in this case.

Given an expression f of function type F ,

calls f with arguments a1, a2, … an . Except for one special case, arguments must be single-valued expressions assignable to the parameter types of F and are evaluated before the function is called. The type of the expression is the result type of F . A method invocation is similar but the method itself is specified as a selector upon a value of the receiver type for the method.

In a function call, the function value and arguments are evaluated in the usual order . After they are evaluated, the parameters of the call are passed by value to the function and the called function begins execution. The return parameters of the function are passed by value back to the caller when the function returns.

Calling a nil function value causes a run-time panic .

As a special case, if the return values of a function or method g are equal in number and individually assignable to the parameters of another function or method f , then the call f(g( parameters_of_g )) will invoke f after binding the return values of g to the parameters of f in order. The call of f must contain no parameters other than the call of g , and g must have at least one return value. If f has a final ... parameter, it is assigned the return values of g that remain after assignment of regular parameters.

A method call x.m() is valid if the method set of (the type of) x contains m and the argument list can be assigned to the parameter list of m . If x is addressable and &x 's method set contains m , x.m() is shorthand for (&x).m() :

There is no distinct method type and there are no method literals.

Passing arguments to ... parameters

If f is variadic with a final parameter p of type ...T , then within f the type of p is equivalent to type []T . If f is invoked with no actual arguments for p , the value passed to p is nil . Otherwise, the value passed is a new slice of type []T with a new underlying array whose successive elements are the actual arguments, which all must be assignable to T . The length and capacity of the slice is therefore the number of arguments bound to p and may differ for each call site.

Given the function and calls

within Greeting , who will have the value nil in the first call, and []string{"Joe", "Anna", "Eileen"} in the second.

If the final argument is assignable to a slice type []T and is followed by ... , it is passed unchanged as the value for a ...T parameter. In this case no new slice is created.

Given the slice s and call

within Greeting , who will have the same value as s with the same underlying array.

Operators combine operands into expressions.

Comparisons are discussed elsewhere . For other binary operators, the operand types must be identical unless the operation involves shifts or untyped constants . For operations involving constants only, see the section on constant expressions .

Except for shift operations, if one operand is an untyped constant and the other operand is not, the constant is implicitly converted to the type of the other operand.

The right operand in a shift expression must have integer type or be an untyped constant representable by a value of type uint . If the left operand of a non-constant shift expression is an untyped constant, it is first implicitly converted to the type it would assume if the shift expression were replaced by its left operand alone.

Operator precedence

There are five precedence levels for binary operators. Multiplication operators bind strongest, followed by addition operators, comparison operators, && (logical AND), and finally || (logical OR):

Binary operators of the same precedence associate from left to right. For instance, x / y * z is the same as (x / y) * z .

Arithmetic operators

Arithmetic operators apply to numeric values and yield a result of the same type as the first operand. The four standard arithmetic operators ( + , - , * , / ) apply to integer, floating-point, and complex types; + also applies to strings. The bitwise logical and shift operators apply to integers only.

Integer operators

For two integer values x and y , the integer quotient q = x / y and remainder r = x % y satisfy the following relationships:

with x / y truncated towards zero ( "truncated division" ).

The one exception to this rule is that if the dividend x is the most negative value for the int type of x , the quotient q = x / -1 is equal to x (and r = 0 ) due to two's-complement integer overflow :

If the divisor is a constant , it must not be zero. If the divisor is zero at run time, a run-time panic occurs. If the dividend is non-negative and the divisor is a constant power of 2, the division may be replaced by a right shift, and computing the remainder may be replaced by a bitwise AND operation:

The shift operators shift the left operand by the shift count specified by the right operand, which must be non-negative. If the shift count is negative at run time, a run-time panic occurs. The shift operators implement arithmetic shifts if the left operand is a signed integer and logical shifts if it is an unsigned integer. There is no upper limit on the shift count. Shifts behave as if the left operand is shifted n times by 1 for a shift count of n . As a result, x << 1 is the same as x*2 and x >> 1 is the same as x/2 but truncated towards negative infinity.

For integer operands, the unary operators + , - , and ^ are defined as follows:

Integer overflow

For unsigned integer values, the operations + , - , * , and << are computed modulo 2 n , where n is the bit width of the unsigned integer 's type. Loosely speaking, these unsigned integer operations discard high bits upon overflow, and programs may rely on "wrap around".

For signed integers, the operations + , - , * , / , and << may legally overflow and the resulting value exists and is deterministically defined by the signed integer representation, the operation, and its operands. Overflow does not cause a run-time panic . A compiler may not optimize code under the assumption that overflow does not occur. For instance, it may not assume that x < x + 1 is always true.

Floating-point operators

For floating-point and complex numbers, +x is the same as x , while -x is the negation of x . The result of a floating-point or complex division by zero is not specified beyond the IEEE-754 standard; whether a run-time panic occurs is implementation-specific.

An implementation may combine multiple floating-point operations into a single fused operation, possibly across statements, and produce a result that differs from the value obtained by executing and rounding the instructions individually. An explicit floating-point type conversion rounds to the precision of the target type, preventing fusion that would discard that rounding.

For instance, some architectures provide a "fused multiply and add" (FMA) instruction that computes x*y + z without rounding the intermediate result x*y . These examples show when a Go implementation can use that instruction:

String concatenation

Strings can be concatenated using the + operator or the += assignment operator:

String addition creates a new string by concatenating the operands.

Comparison operators

Comparison operators compare two operands and yield an untyped boolean value.

In any comparison, the first operand must be assignable to the type of the second operand, or vice versa.

The equality operators == and != apply to operands that are comparable . The ordering operators < , <= , > , and >= apply to operands that are ordered . These terms and the result of the comparisons are defined as follows:

Boolean values are comparable. Two boolean values are equal if they are either both true or both false .
Integer values are comparable and ordered, in the usual way.
Floating-point values are comparable and ordered, as defined by the IEEE-754 standard.
Complex values are comparable. Two complex values u and v are equal if both real(u) == real(v) and imag(u) == imag(v) .
String values are comparable and ordered, lexically byte-wise.
Pointer values are comparable. Two pointer values are equal if they point to the same variable or if both have value nil . Pointers to distinct zero-size variables may or may not be equal.
Channel values are comparable. Two channel values are equal if they were created by the same call to make or if both have value nil .
Interface values are comparable. Two interface values are equal if they have identical dynamic types and equal dynamic values or if both have value nil .
A value x of non-interface type X and a value t of interface type T are comparable when values of type X are comparable and X implements T . They are equal if t 's dynamic type is identical to X and t 's dynamic value is equal to x .
Struct values are comparable if all their fields are comparable. Two struct values are equal if their corresponding non- blank fields are equal.
Array values are comparable if values of the array element type are comparable. Two array values are equal if their corresponding elements are equal.

A comparison of two interface values with identical dynamic types causes a run-time panic if values of that type are not comparable. This behavior applies not only to direct interface value comparisons but also when comparing arrays of interface values or structs with interface-valued fields.

Slice, map, and function values are not comparable. However, as a special case, a slice, map, or function value may be compared to the predeclared identifier nil . Comparison of pointer, channel, and interface values to nil is also allowed and follows from the general rules above.

Logical operators

Logical operators apply to boolean values and yield a result of the same type as the operands. The right operand is evaluated conditionally.

Address operators

For an operand x of type T , the address operation &x generates a pointer of type *T to x . The operand must be addressable , that is, either a variable, pointer indirection, or slice indexing operation; or a field selector of an addressable struct operand; or an array indexing operation of an addressable array. As an exception to the addressability requirement, x may also be a (possibly parenthesized) composite literal . If the evaluation of x would cause a run-time panic , then the evaluation of &x does too.

For an operand x of pointer type *T , the pointer indirection *x denotes the variable of type T pointed to by x . If x is nil , an attempt to evaluate *x will cause a run-time panic .

Receive operator

For an operand ch of channel type , the value of the receive operation <-ch is the value received from the channel ch . The channel direction must permit receive operations, and the type of the receive operation is the element type of the channel. The expression blocks until a value is available. Receiving from a nil channel blocks forever. A receive operation on a closed channel can always proceed immediately, yielding the element type's zero value after any previously sent values have been received.

A receive expression used in an assignment or initialization of the special form

yields an additional untyped boolean result reporting whether the communication succeeded. The value of ok is true if the value received was delivered by a successful send operation to the channel, or false if it is a zero value generated because the channel is closed and empty.

Conversions

A conversion changes the type of an expression to the type specified by the conversion. A conversion may appear literally in the source, or it may be implied by the context in which an expression appears.

An explicit conversion is an expression of the form T(x) where T is a type and x is an expression that can be converted to type T .

If the type starts with the operator * or <- , or if the type starts with the keyword func and has no result list, it must be parenthesized when necessary to avoid ambiguity:

A constant value x can be converted to type T if x is representable by a value of T . As a special case, an integer constant x can be explicitly converted to a string type using the same rule as for non-constant x .

Converting a constant yields a typed constant as result.

A non-constant value x can be converted to type T in any of these cases:

x is assignable to T .
ignoring struct tags (see below), x 's type and T have identical underlying types .
ignoring struct tags (see below), x 's type and T are pointer types that are not defined types , and their pointer base types have identical underlying types.
x 's type and T are both integer or floating point types.
x 's type and T are both complex types.
x is an integer or a slice of bytes or runes and T is a string type.
x is a string and T is a slice of bytes or runes.
x is a slice, T is a pointer to an array, and the slice and array types have identical element types.

Struct tags are ignored when comparing struct types for identity for the purpose of conversion:

Specific rules apply to (non-constant) conversions between numeric types or to and from a string type. These conversions may change the representation of x and incur a run-time cost. All other conversions only change the type but not the representation of x .

There is no linguistic mechanism to convert between pointers and integers. The package unsafe implements this functionality under restricted circumstances.

Conversions between numeric types

For the conversion of non-constant numeric values, the following rules apply:

When converting between integer types, if the value is a signed integer, it is sign extended to implicit infinite precision; otherwise it is zero extended. It is then truncated to fit in the result type's size. For example, if v := uint16(0x10F0) , then uint32(int8(v)) == 0xFFFFFFF0 . The conversion always yields a valid value; there is no indication of overflow.
When converting a floating-point number to an integer, the fraction is discarded (truncation towards zero).
When converting an integer or floating-point number to a floating-point type, or a complex number to another complex type, the result value is rounded to the precision specified by the destination type. For instance, the value of a variable x of type float32 may be stored using additional precision beyond that of an IEEE-754 32-bit number, but float32(x) represents the result of rounding x 's value to 32-bit precision. Similarly, x + 0.1 may use more than 32 bits of precision, but float32(x + 0.1) does not.

In all non-constant conversions involving floating-point or complex values, if the result type cannot represent the value the conversion succeeds but the result value is implementation-dependent.

Conversions to and from a string type

Converting a signed or unsigned integer value to a string type yields a string containing the UTF-8 representation of the integer. Values outside the range of valid Unicode code points are converted to "\uFFFD" . string('a') // "a" string(-1) // "\ufffd" == "\xef\xbf\xbd" string(0xf8) // "\u00f8" == "ø" == "\xc3\xb8" type MyString string MyString(0x65e5) // "\u65e5" == "日" == "\xe6\x97\xa5"
Converting a slice of bytes to a string type yields a string whose successive bytes are the elements of the slice. string([]byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}) // "hellø" string([]byte{}) // "" string([]byte(nil)) // "" type MyBytes []byte string(MyBytes{'h', 'e', 'l', 'l', '\xc3', '\xb8'}) // "hellø"
Converting a slice of runes to a string type yields a string that is the concatenation of the individual rune values converted to strings. string([]rune{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔" string([]rune{}) // "" string([]rune(nil)) // "" type MyRunes []rune string(MyRunes{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔"
Converting a value of a string type to a slice of bytes type yields a slice whose successive elements are the bytes of the string. []byte("hellø") // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'} []byte("") // []byte{} MyBytes("hellø") // []byte{'h', 'e', 'l', 'l', '\xc3', '\xb8'}
Converting a value of a string type to a slice of runes type yields a slice containing the individual Unicode code points of the string. []rune(MyString("白鵬翔")) // []rune{0x767d, 0x9d6c, 0x7fd4} []rune("") // []rune{} MyRunes("白鵬翔") // []rune{0x767d, 0x9d6c, 0x7fd4}

Conversions from slice to array pointer

Converting a slice to an array pointer yields a pointer to the underlying array of the slice. If the length of the slice is less than the length of the array, a run-time panic occurs.

Constant expressions

Constant expressions may contain only constant operands and are evaluated at compile time.

Untyped boolean, numeric, and string constants may be used as operands wherever it is legal to use an operand of boolean, numeric, or string type, respectively.

A constant comparison always yields an untyped boolean constant. If the left operand of a constant shift expression is an untyped constant, the result is an integer constant; otherwise it is a constant of the same type as the left operand, which must be of integer type .

Any other operation on untyped constants results in an untyped constant of the same kind; that is, a boolean, integer, floating-point, complex, or string constant. If the untyped operands of a binary operation (other than a shift) are of different kinds, the result is of the operand's kind that appears later in this list: integer, rune, floating-point, complex. For example, an untyped integer constant divided by an untyped complex constant yields an untyped complex constant.

Applying the built-in function complex to untyped integer, rune, or floating-point constants yields an untyped complex constant.

Constant expressions are always evaluated exactly; intermediate values and the constants themselves may require precision significantly larger than supported by any predeclared type in the language. The following are legal declarations:

The divisor of a constant division or remainder operation must not be zero:

The values of typed constants must always be accurately representable by values of the constant type. The following constant expressions are illegal:

The mask used by the unary bitwise complement operator ^ matches the rule for non-constants: the mask is all 1s for unsigned constants and -1 for signed and untyped constants.

Implementation restriction: A compiler may use rounding while computing untyped floating-point or complex constant expressions; see the implementation restriction in the section on constants . This rounding may cause a floating-point constant expression to be invalid in an integer context, even if it would be integral when calculated using infinite precision, and vice versa.

Order of evaluation

At package level, initialization dependencies determine the evaluation order of individual initialization expressions in variable declarations . Otherwise, when evaluating the operands of an expression, assignment, or return statement , all function calls, method calls, and communication operations are evaluated in lexical left-to-right order.

For example, in the (function-local) assignment

the function calls and communication happen in the order f() , h() , i() , j() , <-c , g() , and k() . However, the order of those events compared to the evaluation and indexing of x and the evaluation of y is not specified.

At package level, initialization dependencies override the left-to-right rule for individual initialization expressions, but not for operands within each expression:

The function calls happen in the order u() , sqr() , v() , f() , v() , and g() .

Floating-point operations within a single expression are evaluated according to the associativity of the operators. Explicit parentheses affect the evaluation by overriding the default associativity. In the expression x + (y + z) the addition y + z is performed before adding x .

Statements control execution.

Terminating statements

A terminating statement prevents execution of all statements that lexically appear after it in the same block . The following statements are terminating:

A "return" or "goto" statement.
A call to the built-in function panic .
A block in which the statement list ends in a terminating statement.
the "else" branch is present, and
both branches are terminating statements.
there are no "break" statements referring to the "for" statement, and
the loop condition is absent.
there are no "break" statements referring to the "switch" statement,
there is a default case, and
the statement lists in each case, including the default, end in a terminating statement, or a possibly labeled "fallthrough" statement .
there are no "break" statements referring to the "select" statement, and
the statement lists in each case, including the default if present, end in a terminating statement.
A labeled statement labeling a terminating statement.

All other statements are not terminating.

A statement list ends in a terminating statement if the list is not empty and its final non-empty statement is terminating.

Empty statements

The empty statement does nothing.

Labeled statements

A labeled statement may be the target of a goto , break or continue statement.

Expression statements

With the exception of specific built-in functions, function and method calls and receive operations can appear in statement context. Such statements may be parenthesized.

The following built-in functions are not permitted in statement context:

Send statements

A send statement sends a value on a channel. The channel expression must be of channel type , the channel direction must permit send operations, and the type of the value to be sent must be assignable to the channel's element type.

Both the channel and the value expression are evaluated before communication begins. Communication blocks until the send can proceed. A send on an unbuffered channel can proceed if a receiver is ready. A send on a buffered channel can proceed if there is room in the buffer. A send on a closed channel proceeds by causing a run-time panic . A send on a nil channel blocks forever.

IncDec statements

The "++" and "--" statements increment or decrement their operands by the untyped constant 1 . As with an assignment, the operand must be addressable or a map index expression.

The following assignment statements are semantically equivalent:

Assignments

Each left-hand side operand must be addressable , a map index expression, or (for = assignments only) the blank identifier . Operands may be parenthesized.

An assignment operation x op = y where op is a binary arithmetic operator is equivalent to x = x op (y) but evaluates x only once. The op = construct is a single token. In assignment operations, both the left- and right-hand expression lists must contain exactly one single-valued expression, and the left-hand expression must not be the blank identifier.

A tuple assignment assigns the individual elements of a multi-valued operation to a list of variables. There are two forms. In the first, the right hand operand is a single multi-valued expression such as a function call, a channel or map operation, or a type assertion . The number of operands on the left hand side must match the number of values. For instance, if f is a function returning two values,

assigns the first value to x and the second to y . In the second form, the number of operands on the left must equal the number of expressions on the right, each of which must be single-valued, and the n th expression on the right is assigned to the n th operand on the left:

The blank identifier provides a way to ignore right-hand side values in an assignment:

The assignment proceeds in two phases. First, the operands of index expressions and pointer indirections (including implicit pointer indirections in selectors ) on the left and the expressions on the right are all evaluated in the usual order . Second, the assignments are carried out in left-to-right order.

In assignments, each value must be assignable to the type of the operand to which it is assigned, with the following special cases:

Any typed value may be assigned to the blank identifier.
If an untyped constant is assigned to a variable of interface type or the blank identifier, the constant is first implicitly converted to its default type .
If an untyped boolean value is assigned to a variable of interface type or the blank identifier, it is first implicitly converted to type bool .

If statements

"If" statements specify the conditional execution of two branches according to the value of a boolean expression. If the expression evaluates to true, the "if" branch is executed, otherwise, if present, the "else" branch is executed.

The expression may be preceded by a simple statement, which executes before the expression is evaluated.

Switch statements

"Switch" statements provide multi-way execution. An expression or type is compared to the "cases" inside the "switch" to determine which branch to execute.

There are two forms: expression switches and type switches. In an expression switch, the cases contain expressions that are compared against the value of the switch expression. In a type switch, the cases contain types that are compared against the type of a specially annotated switch expression. The switch expression is evaluated exactly once in a switch statement.

Expression switches

In an expression switch, the switch expression is evaluated and the case expressions, which need not be constants, are evaluated left-to-right and top-to-bottom; the first one that equals the switch expression triggers execution of the statements of the associated case; the other cases are skipped. If no case matches and there is a "default" case, its statements are executed. There can be at most one default case and it may appear anywhere in the "switch" statement. A missing switch expression is equivalent to the boolean value true .

If the switch expression evaluates to an untyped constant, it is first implicitly converted to its default type . The predeclared untyped value nil cannot be used as a switch expression. The switch expression type must be comparable .

If a case expression is untyped, it is first implicitly converted to the type of the switch expression. For each (possibly converted) case expression x and the value t of the switch expression, x == t must be a valid comparison .

In other words, the switch expression is treated as if it were used to declare and initialize a temporary variable t without explicit type; it is that value of t against which each case expression x is tested for equality.

In a case or default clause, the last non-empty statement may be a (possibly labeled ) "fallthrough" statement to indicate that control should flow from the end of this clause to the first statement of the next clause. Otherwise control flows to the end of the "switch" statement. A "fallthrough" statement may appear as the last statement of all but the last clause of an expression switch.

The switch expression may be preceded by a simple statement, which executes before the expression is evaluated.

Implementation restriction: A compiler may disallow multiple case expressions evaluating to the same constant. For instance, the current compilers disallow duplicate integer, floating point, or string constants in case expressions.

Type switches

A type switch compares types rather than values. It is otherwise similar to an expression switch. It is marked by a special switch expression that has the form of a type assertion using the keyword type rather than an actual type:

Cases then match actual types T against the dynamic type of the expression x . As with type assertions, x must be of interface type , and each non-interface type T listed in a case must implement the type of x . The types listed in the cases of a type switch must all be different .

The TypeSwitchGuard may include a short variable declaration . When that form is used, the variable is declared at the end of the TypeSwitchCase in the implicit block of each clause. In clauses with a case listing exactly one type, the variable has that type; otherwise, the variable has the type of the expression in the TypeSwitchGuard.

Instead of a type, a case may use the predeclared identifier nil ; that case is selected when the expression in the TypeSwitchGuard is a nil interface value. There may be at most one nil case.

Given an expression x of type interface{} , the following type switch:

could be rewritten:

The type switch guard may be preceded by a simple statement, which executes before the guard is evaluated.

The "fallthrough" statement is not permitted in a type switch.

For statements

A "for" statement specifies repeated execution of a block. There are three forms: The iteration may be controlled by a single condition, a "for" clause, or a "range" clause.

For statements with single condition

In its simplest form, a "for" statement specifies the repeated execution of a block as long as a boolean condition evaluates to true. The condition is evaluated before each iteration. If the condition is absent, it is equivalent to the boolean value true .

For statements with for clause

A "for" statement with a ForClause is also controlled by its condition, but additionally it may specify an init and a post statement, such as an assignment, an increment or decrement statement. The init statement may be a short variable declaration , but the post statement must not. Variables declared by the init statement are re-used in each iteration.

If non-empty, the init statement is executed once before evaluating the condition for the first iteration; the post statement is executed after each execution of the block (and only if the block was executed). Any element of the ForClause may be empty but the semicolons are required unless there is only a condition. If the condition is absent, it is equivalent to the boolean value true .

For statements with range clause

A "for" statement with a "range" clause iterates through all entries of an array, slice, string or map, or values received on a channel. For each entry it assigns iteration values to corresponding iteration variables if present and then executes the block.

The expression on the right in the "range" clause is called the range expression , which may be an array, pointer to an array, slice, string, map, or channel permitting receive operations . As with an assignment, if present the operands on the left must be addressable or map index expressions; they denote the iteration variables. If the range expression is a channel, at most one iteration variable is permitted, otherwise there may be up to two. If the last iteration variable is the blank identifier , the range clause is equivalent to the same clause without that identifier.

The range expression x is evaluated once before beginning the loop, with one exception: if at most one iteration variable is present and len(x) is constant , the range expression is not evaluated.

Function calls on the left are evaluated once per iteration. For each iteration, iteration values are produced as follows if the respective iteration variables are present:

For an array, pointer to array, or slice value a , the index iteration values are produced in increasing order, starting at element index 0. If at most one iteration variable is present, the range loop produces iteration values from 0 up to len(a)-1 and does not index into the array or slice itself. For a nil slice, the number of iterations is 0.
For a string value, the "range" clause iterates over the Unicode code points in the string starting at byte index 0. On successive iterations, the index value will be the index of the first byte of successive UTF-8-encoded code points in the string, and the second value, of type rune , will be the value of the corresponding code point. If the iteration encounters an invalid UTF-8 sequence, the second value will be 0xFFFD , the Unicode replacement character, and the next iteration will advance a single byte in the string.
The iteration order over maps is not specified and is not guaranteed to be the same from one iteration to the next. If a map entry that has not yet been reached is removed during iteration, the corresponding iteration value will not be produced. If a map entry is created during iteration, that entry may be produced during the iteration or may be skipped. The choice may vary for each entry created and from one iteration to the next. If the map is nil , the number of iterations is 0.
For channels, the iteration values produced are the successive values sent on the channel until the channel is closed . If the channel is nil , the range expression blocks forever.

The iteration values are assigned to the respective iteration variables as in an assignment statement .

The iteration variables may be declared by the "range" clause using a form of short variable declaration ( := ). In this case their types are set to the types of the respective iteration values and their scope is the block of the "for" statement; they are re-used in each iteration. If the iteration variables are declared outside the "for" statement, after execution their values will be those of the last iteration.

Go statements

A "go" statement starts the execution of a function call as an independent concurrent thread of control, or goroutine , within the same address space.

The expression must be a function or method call; it cannot be parenthesized. Calls of built-in functions are restricted as for expression statements .

The function value and parameters are evaluated as usual in the calling goroutine, but unlike with a regular call, program execution does not wait for the invoked function to complete. Instead, the function begins executing independently in a new goroutine. When the function terminates, its goroutine also terminates. If the function has any return values, they are discarded when the function completes.

Select statements

A "select" statement chooses which of a set of possible send or receive operations will proceed. It looks similar to a "switch" statement but with the cases all referring to communication operations.

A case with a RecvStmt may assign the result of a RecvExpr to one or two variables, which may be declared using a short variable declaration . The RecvExpr must be a (possibly parenthesized) receive operation. There can be at most one default case and it may appear anywhere in the list of cases.

Execution of a "select" statement proceeds in several steps:

For all the cases in the statement, the channel operands of receive operations and the channel and right-hand-side expressions of send statements are evaluated exactly once, in source order, upon entering the "select" statement. The result is a set of channels to receive from or send to, and the corresponding values to send. Any side effects in that evaluation will occur irrespective of which (if any) communication operation is selected to proceed. Expressions on the left-hand side of a RecvStmt with a short variable declaration or assignment are not yet evaluated.
If one or more of the communications can proceed, a single one that can proceed is chosen via a uniform pseudo-random selection. Otherwise, if there is a default case, that case is chosen. If there is no default case, the "select" statement blocks until at least one of the communications can proceed.
Unless the selected case is the default case, the respective communication operation is executed.
If the selected case is a RecvStmt with a short variable declaration or an assignment, the left-hand side expressions are evaluated and the received value (or values) are assigned.
The statement list of the selected case is executed.

Since communication on nil channels can never proceed, a select with only nil channels and no default case blocks forever.

Return statements

A "return" statement in a function F terminates the execution of F , and optionally provides one or more result values. Any functions deferred by F are executed before F returns to its caller.

In a function without a result type, a "return" statement must not specify any result values.

There are three ways to return values from a function with a result type:

The return value or values may be explicitly listed in the "return" statement. Each expression must be single-valued and assignable to the corresponding element of the function's result type. func simpleF() int { return 2 } func complexF1() (re float64, im float64) { return -7.0, -4.0 }
The expression list in the "return" statement may be a single call to a multi-valued function. The effect is as if each value returned from that function were assigned to a temporary variable with the type of the respective value, followed by a "return" statement listing these variables, at which point the rules of the previous case apply. func complexF2() (re float64, im float64) { return complexF1() }
The expression list may be empty if the function's result type specifies names for its result parameters . The result parameters act as ordinary local variables and the function may assign values to them as necessary. The "return" statement returns the values of these variables. func complexF3() (re float64, im float64) { re = 7.0 im = 4.0 return } func (devnull) Write(p []byte) (n int, _ error) { n = len(p) return }

Regardless of how they are declared, all the result values are initialized to the zero values for their type upon entry to the function. A "return" statement that specifies results sets the result parameters before any deferred functions are executed.

Implementation restriction: A compiler may disallow an empty expression list in a "return" statement if a different entity (constant, type, or variable) with the same name as a result parameter is in scope at the place of the return.

Break statements

A "break" statement terminates execution of the innermost "for" , "switch" , or "select" statement within the same function.

If there is a label, it must be that of an enclosing "for", "switch", or "select" statement, and that is the one whose execution terminates.

Continue statements

A "continue" statement begins the next iteration of the innermost "for" loop at its post statement. The "for" loop must be within the same function.

If there is a label, it must be that of an enclosing "for" statement, and that is the one whose execution advances.

Goto statements

A "goto" statement transfers control to the statement with the corresponding label within the same function.

Executing the "goto" statement must not cause any variables to come into scope that were not already in scope at the point of the goto. For instance, this example:

is erroneous because the jump to label L skips the creation of v .

A "goto" statement outside a block cannot jump to a label inside that block. For instance, this example:

is erroneous because the label L1 is inside the "for" statement's block but the goto is not.

Fallthrough statements

A "fallthrough" statement transfers control to the first statement of the next case clause in an expression "switch" statement . It may be used only as the final non-empty statement in such a clause.

Defer statements

A "defer" statement invokes a function whose execution is deferred to the moment the surrounding function returns, either because the surrounding function executed a return statement , reached the end of its function body , or because the corresponding goroutine is panicking .

Each time a "defer" statement executes, the function value and parameters to the call are evaluated as usual and saved anew but the actual function is not invoked. Instead, deferred functions are invoked immediately before the surrounding function returns, in the reverse order they were deferred. That is, if the surrounding function returns through an explicit return statement , deferred functions are executed after any result parameters are set by that return statement but before the function returns to its caller. If a deferred function value evaluates to nil , execution panics when the function is invoked, not when the "defer" statement is executed.

For instance, if the deferred function is a function literal and the surrounding function has named result parameters that are in scope within the literal, the deferred function may access and modify the result parameters before they are returned. If the deferred function has any return values, they are discarded when the function completes. (See also the section on handling panics .)

Built-in functions

Built-in functions are predeclared . They are called like any other function but some of them accept a type instead of an expression as the first argument.

The built-in functions do not have standard Go types, so they can only appear in call expressions ; they cannot be used as function values.

For a channel c , the built-in function close(c) records that no more values will be sent on the channel. It is an error if c is a receive-only channel. Sending to or closing a closed channel causes a run-time panic . Closing the nil channel also causes a run-time panic . After calling close , and after any previously sent values have been received, receive operations will return the zero value for the channel's type without blocking. The multi-valued receive operation returns a received value along with an indication of whether the channel is closed.

Length and capacity

The built-in functions len and cap take arguments of various types and return a result of type int . The implementation guarantees that the result always fits into an int .

The capacity of a slice is the number of elements for which there is space allocated in the underlying array. At any time the following relationship holds:

The length of a nil slice, map or channel is 0. The capacity of a nil slice or channel is 0.

The expression len(s) is constant if s is a string constant. The expressions len(s) and cap(s) are constants if the type of s is an array or pointer to an array and the expression s does not contain channel receives or (non-constant) function calls ; in this case s is not evaluated. Otherwise, invocations of len and cap are not constant and s is evaluated.

The built-in function new takes a type T , allocates storage for a variable of that type at run time, and returns a value of type *T pointing to it. The variable is initialized as described in the section on initial values .

For instance

allocates storage for a variable of type S , initializes it ( a=0 , b=0.0 ), and returns a value of type *S containing the address of the location.

Making slices, maps and channels

The built-in function make takes a type T , which must be a slice, map or channel type, optionally followed by a type-specific list of expressions. It returns a value of type T (not *T ). The memory is initialized as described in the section on initial values .

Each of the size arguments n and m must be of integer type or an untyped constant . A constant size argument must be non-negative and representable by a value of type int ; if it is an untyped constant it is given type int . If both n and m are provided and are constant, then n must be no larger than m . If n is negative or larger than m at run time, a run-time panic occurs.

Calling make with a map type and size hint n will create a map with initial space to hold n map elements. The precise behavior is implementation-dependent.

Appending to and copying slices

The built-in functions append and copy assist in common slice operations. For both functions, the result is independent of whether the memory referenced by the arguments overlaps.

The variadic function append appends zero or more values x to s of type S , which must be a slice type, and returns the resulting slice, also of type S . The values x are passed to a parameter of type ...T where T is the element type of S and the respective parameter passing rules apply. As a special case, append also accepts a first argument assignable to type []byte with a second argument of string type followed by ... . This form appends the bytes of the string.

If the capacity of s is not large enough to fit the additional values, append allocates a new, sufficiently large underlying array that fits both the existing slice elements and the additional values. Otherwise, append re-uses the underlying array.

The function copy copies slice elements from a source src to a destination dst and returns the number of elements copied. Both arguments must have identical element type T and must be assignable to a slice of type []T . The number of elements copied is the minimum of len(src) and len(dst) . As a special case, copy also accepts a destination argument assignable to type []byte with a source argument of a string type. This form copies the bytes from the string into the byte slice.

Deletion of map elements

The built-in function delete removes the element with key k from a map m . The type of k must be assignable to the key type of m .

If the map m is nil or the element m[k] does not exist, delete is a no-op.

Manipulating complex numbers

Three functions assemble and disassemble complex numbers. The built-in function complex constructs a complex value from a floating-point real and imaginary part, while real and imag extract the real and imaginary parts of a complex value.

The type of the arguments and return value correspond. For complex , the two arguments must be of the same floating-point type and the return type is the complex type with the corresponding floating-point constituents: complex64 for float32 arguments, and complex128 for float64 arguments. If one of the arguments evaluates to an untyped constant, it is first implicitly converted to the type of the other argument. If both arguments evaluate to untyped constants, they must be non-complex numbers or their imaginary parts must be zero, and the return value of the function is an untyped complex constant.

For real and imag , the argument must be of complex type, and the return type is the corresponding floating-point type: float32 for a complex64 argument, and float64 for a complex128 argument. If the argument evaluates to an untyped constant, it must be a number, and the return value of the function is an untyped floating-point constant.

The real and imag functions together form the inverse of complex , so for a value z of a complex type Z , z == Z(complex(real(z), imag(z))) .

If the operands of these functions are all constants, the return value is a constant.

Handling panics

Two built-in functions, panic and recover , assist in reporting and handling run-time panics and program-defined error conditions.

While executing a function F , an explicit call to panic or a run-time panic terminates the execution of F . Any functions deferred by F are then executed as usual. Next, any deferred functions run by F's caller are run, and so on up to any deferred by the top-level function in the executing goroutine. At that point, the program is terminated and the error condition is reported, including the value of the argument to panic . This termination sequence is called panicking .

The recover function allows a program to manage behavior of a panicking goroutine. Suppose a function G defers a function D that calls recover and a panic occurs in a function on the same goroutine in which G is executing. When the running of deferred functions reaches D , the return value of D 's call to recover will be the value passed to the call of panic . If D returns normally, without starting a new panic , the panicking sequence stops. In that case, the state of functions called between G and the call to panic is discarded, and normal execution resumes. Any functions deferred by G before D are then run and G 's execution terminates by returning to its caller.

The return value of recover is nil if any of the following conditions holds:

panic 's argument was nil ;
the goroutine is not panicking;
recover was not called directly by a deferred function.

The protect function in the example below invokes the function argument g and protects callers from run-time panics raised by g .

Bootstrapping

Current implementations provide several built-in functions useful during bootstrapping. These functions are documented for completeness but are not guaranteed to stay in the language. They do not return a result.

Implementation restriction: print and println need not accept arbitrary argument types, but printing of boolean, numeric, and string types must be supported.

Go programs are constructed by linking together packages . A package in turn is constructed from one or more source files that together declare constants, types, variables and functions belonging to the package and which are accessible in all files of the same package. Those elements may be exported and used in another package.

Source file organization

Each source file consists of a package clause defining the package to which it belongs, followed by a possibly empty set of import declarations that declare packages whose contents it wishes to use, followed by a possibly empty set of declarations of functions, types, variables, and constants.

Package clause

A package clause begins each source file and defines the package to which the file belongs.

The PackageName must not be the blank identifier .

A set of files sharing the same PackageName form the implementation of a package. An implementation may require that all source files for a package inhabit the same directory.

Import declarations

An import declaration states that the source file containing the declaration depends on functionality of the imported package ( §Program initialization and execution ) and enables access to exported identifiers of that package. The import names an identifier (PackageName) to be used for access and an ImportPath that specifies the package to be imported.

The PackageName is used in qualified identifiers to access exported identifiers of the package within the importing source file. It is declared in the file block . If the PackageName is omitted, it defaults to the identifier specified in the package clause of the imported package. If an explicit period ( . ) appears instead of a name, all the package's exported identifiers declared in that package's package block will be declared in the importing source file's file block and must be accessed without a qualifier.

The interpretation of the ImportPath is implementation-dependent but it is typically a substring of the full file name of the compiled package and may be relative to a repository of installed packages.

Implementation restriction: A compiler may restrict ImportPaths to non-empty strings using only characters belonging to Unicode's L, M, N, P, and S general categories (the Graphic characters without spaces) and may also exclude the characters !"#$%&'()*,:;<=>?[\]^`{|} and the Unicode replacement character U+FFFD.

Assume we have compiled a package containing the package clause package math , which exports function Sin , and installed the compiled package in the file identified by "lib/math" . This table illustrates how Sin is accessed in files that import the package after the various types of import declaration.

An import declaration declares a dependency relation between the importing and imported package. It is illegal for a package to import itself, directly or indirectly, or to directly import a package without referring to any of its exported identifiers. To import a package solely for its side-effects (initialization), use the blank identifier as explicit package name:

An example package

Here is a complete Go package that implements a concurrent prime sieve.

Program initialization and execution

The zero value.

When storage is allocated for a variable , either through a declaration or a call of new , or when a new value is created, either through a composite literal or a call of make , and no explicit initialization is provided, the variable or value is given a default value. Each element of such a variable or value is set to the zero value for its type: false for booleans, 0 for numeric types, "" for strings, and nil for pointers, functions, interfaces, slices, channels, and maps. This initialization is done recursively, so for instance each element of an array of structs will have its fields zeroed if no value is specified.

These two simple declarations are equivalent:

the following holds:

The same would also be true after

Package initialization

Within a package, package-level variable initialization proceeds stepwise, with each step selecting the variable earliest in declaration order which has no dependencies on uninitialized variables.

More precisely, a package-level variable is considered ready for initialization if it is not yet initialized and either has no initialization expression or its initialization expression has no dependencies on uninitialized variables. Initialization proceeds by repeatedly initializing the next package-level variable that is earliest in declaration order and ready for initialization, until there are no variables ready for initialization.

If any variables are still uninitialized when this process ends, those variables are part of one or more initialization cycles, and the program is not valid.

Multiple variables on the left-hand side of a variable declaration initialized by single (multi-valued) expression on the right-hand side are initialized together: If any of the variables on the left-hand side is initialized, all those variables are initialized in the same step.

For the purpose of package initialization, blank variables are treated like any other variables in declarations.

The declaration order of variables declared in multiple files is determined by the order in which the files are presented to the compiler: Variables declared in the first file are declared before any of the variables declared in the second file, and so on.

Dependency analysis does not rely on the actual values of the variables, only on lexical references to them in the source, analyzed transitively. For instance, if a variable x 's initialization expression refers to a function whose body refers to variable y then x depends on y . Specifically:

A reference to a variable or function is an identifier denoting that variable or function.
A reference to a method m is a method value or method expression of the form t.m , where the (static) type of t is not an interface type, and the method m is in the method set of t . It is immaterial whether the resulting function value t.m is invoked.
A variable, function, or method x depends on a variable y if x 's initialization expression or body (for functions and methods) contains a reference to y or to a function or method that depends on y .

For example, given the declarations

the initialization order is d , b , c , a . Note that the order of subexpressions in initialization expressions is irrelevant: a = c + b and a = b + c result in the same initialization order in this example.

Dependency analysis is performed per package; only references referring to variables, functions, and (non-interface) methods declared in the current package are considered. If other, hidden, data dependencies exists between variables, the initialization order between those variables is unspecified.

For instance, given the declarations

the variable a will be initialized after b but whether x is initialized before b , between b and a , or after a , and thus also the moment at which sideEffect() is called (before or after x is initialized) is not specified.

Variables may also be initialized using functions named init declared in the package block, with no arguments and no result parameters.

Multiple such functions may be defined per package, even within a single source file. In the package block, the init identifier can be used only to declare init functions, yet the identifier itself is not declared . Thus init functions cannot be referred to from anywhere in a program.

A package with no imports is initialized by assigning initial values to all its package-level variables followed by calling all init functions in the order they appear in the source, possibly in multiple files, as presented to the compiler. If a package has imports, the imported packages are initialized before initializing the package itself. If multiple packages import a package, the imported package will be initialized only once. The importing of packages, by construction, guarantees that there can be no cyclic initialization dependencies.

Package initialization—variable initialization and the invocation of init functions—happens in a single goroutine, sequentially, one package at a time. An init function may launch other goroutines, which can run concurrently with the initialization code. However, initialization always sequences the init functions: it will not invoke the next one until the previous one has returned.

To ensure reproducible initialization behavior, build systems are encouraged to present multiple files belonging to the same package in lexical file name order to a compiler.

Program execution

A complete program is created by linking a single, unimported package called the main package with all the packages it imports, transitively. The main package must have package name main and declare a function main that takes no arguments and returns no value.

Program execution begins by initializing the main package and then invoking the function main . When that function invocation returns, the program exits. It does not wait for other (non- main ) goroutines to complete.

The predeclared type error is defined as

It is the conventional interface for representing an error condition, with the nil value representing no error. For instance, a function to read data from a file might be defined:

Run-time panics

Execution errors such as attempting to index an array out of bounds trigger a run-time panic equivalent to a call of the built-in function panic with a value of the implementation-defined interface type runtime.Error . That type satisfies the predeclared interface type error . The exact error values that represent distinct run-time error conditions are unspecified.

System considerations

Package unsafe.

The built-in package unsafe , known to the compiler and accessible through the import path "unsafe" , provides facilities for low-level programming including operations that violate the type system. A package using unsafe must be vetted manually for type safety and may not be portable. The package provides the following interface:

A Pointer is a pointer type but a Pointer value may not be dereferenced . Any pointer or value of underlying type uintptr can be converted to a type of underlying type Pointer and vice versa. The effect of converting between Pointer and uintptr is implementation-defined.

The functions Alignof and Sizeof take an expression x of any type and return the alignment or size, respectively, of a hypothetical variable v as if v was declared via var v = x .

The function Offsetof takes a (possibly parenthesized) selector s.f , denoting a field f of the struct denoted by s or *s , and returns the field offset in bytes relative to the struct's address. If f is an embedded field , it must be reachable without pointer indirections through fields of the struct. For a struct s with field f :

Computer architectures may require memory addresses to be aligned ; that is, for addresses of a variable to be a multiple of a factor, the variable's type's alignment . The function Alignof takes an expression denoting a variable of any type and returns the alignment of the (type of the) variable in bytes. For a variable x :

Calls to Alignof , Offsetof , and Sizeof are compile-time constant expressions of type uintptr .

The function Add adds len to ptr and returns the updated pointer unsafe.Pointer(uintptr(ptr) + uintptr(len)) . The len argument must be of integer type or an untyped constant . A constant len argument must be representable by a value of type int ; if it is an untyped constant it is given type int . The rules for valid uses of Pointer still apply.

The function Slice returns a slice whose underlying array starts at ptr and whose length and capacity are len . Slice(ptr, len) is equivalent to

except that, as a special case, if ptr is nil and len is zero, Slice returns nil .

The len argument must be of integer type or an untyped constant . A constant len argument must be non-negative and representable by a value of type int ; if it is an untyped constant it is given type int . At run time, if len is negative, or if ptr is nil and len is not zero, a run-time panic occurs.

Size and alignment guarantees

For the numeric types , the following sizes are guaranteed:

The following minimal alignment properties are guaranteed:

For a variable x of any type: unsafe.Alignof(x) is at least 1.
For a variable x of struct type: unsafe.Alignof(x) is the largest of all the values unsafe.Alignof(x.f) for each field f of x , but at least 1.
For a variable x of array type: unsafe.Alignof(x) is the same as the alignment of a variable of the array's element type.

A struct or array type has size zero if it contains no fields (or elements, respectively) that have a size greater than zero. Two distinct zero-size variables may have the same address in memory.

Go Introduction
Logging in Golang
time package Golang
Functions in Golang
String literals in
Error handling Golang
Go Features
Go Installation
Go Hello World
Comments in Go
Go Language Keywords
Go Data Types
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Type Conversion in Go
Packages in Go

Go Operators

If-Else Statement
Loops in Go
Break statement
Continue statement
Go Switch Statements
Concurrency in Go
Slices in Go
Strings in Go
Maps in GoLang
Structs in Go
Why is Golang
extract html comments
Golang brute force
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Bar code Golang
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Install/Setup Golang locally
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WebApp in Go

An Operator is a symbol that is used to perform logical or mathematical tasks. Go provides us different types of built-in operators, these mainly are:

Arithmetic Operators

Assignment operators, relational operators, logical operators, bitwise operators.

In this tutorial, we will explore all the built-in operators that Go provides us. Let's explore them one by one.

Arithmetic operators are those operators that are used to perform basic arithmetic operations like addition , subtraction , division, etc. In Go, the common arithmetic operators work on both the integer and float data types. The arithmetic operators can also be split into two subcategories, and these are:

Binary Operators

Unary operators.

The binary operators are those that involve two operands . In Go, we have four binary operators, and these are:

Example: Addition Operator

The addition operator is denoted by the symbol + and is used to perform the addition operation in Go. This operator is mainly used with numbers but it also works with strings.

Consider the example shown below:

5 studytonight

Example: Divison Operator

The division Operator is used when we want to perform some dividing operations and the symbol for the division operator is / . It should be noted that the division operator's result is floored, for example, if we do something like 4 / 3 the answer we will get is 1 instead of 1.3333...

Also, if we divide anything with 0, it will cause the program to crash , and a run-time panic occurs. Also, division with 0.0 wich floating-point numbers gives an infinite result: +Inf

Example: Modulus Operator

The modulus operator is used when we want to extract the remainder of a division operation. The symbol for the modulus operator is % .

Example: Multiplication Operator

The multiplication operator is used when we want to perform simple multiplication of two operands . The symbol used for the multiplication operator in Go is * .

In Programming, the assignment operators are the operators that are used to assign a value to a variable. The most basic assignment operator is denoted by the = symbol. The value on the left of the = symbol is known as the left operand the value on the right of the = symbol is known as the right operand. In Go, we have different assignment operators available, these are mentioned in the table shown below.

It should be noted that all these assignment operators that include two symbols in the format += or -=, simply mean that we are using the arithmetic operator and the simple assignment operator at the same time. In simple mathematical sense, a += 2 is the same as a = a + 2.

Now that we know about the different types of assignment operators let's make use of all these operators in a Go example.

Consider the example shown below

a now is: 4 a now is: 8 a now is: 4 a now is: 16 a now is: 4 a now is: 0 a now is: 0 a now is: 4 a now is: 4

A unary operator is an operator that is used on a single operand only.

There are only two unary operators that come under the category of the arithmetic operators and these are:

Increment Operator

Decrement operator.

The purpose of the increment operator is to increase the value of the operand by one. The symbol used to represent the increment operator is ++ .

It should be noted that both the unary operators can be applied after the operand(number) and not before. Go doesn't support anything like ++operand or --operand .

The purpose of the increment operator is to decrease the value of the operand by one. The symbol used to represent the increment operator is ++ .

Another key point to note that the unary operators cannot be used as expressions in Go . You might have seen something like f(a++) in other programming languages, where f() is a call to a function and we are passing a unary operator as an argument, this is not valid in Go and hence cannot be used.

./prog.go:9:15: syntax error: unexpected ++, expecting comma or )

There are different relational operators that are present in Go, these are:

Let's explore all the operators with the help of different tables that represents how they work and lastly we will see a code example of all of them.

Go is very strict about the values that are compared. It demands that values have to be of the same type. If one of them is a constant, it must be of a type compatible with the other. If these conditions are not satisfied, one of the values has first to be converted to the other’s type. <, <=, >, >=, == and != not only work on number types but also on strings.

They are called logical because the result value of these operators is of type bool.

Now let's explore all these operators in a Go program, consider the example shown below:

false true true false true false

Boolean constants and variables can also be combined with logical operators to produce a boolean value. Such a logical statement is not a complete Go statement in itself. Go has three boolean logical operators: AND and OR is binary operators where NOT is a unary operator. The && and || operators behave in a shortcut way that when the value of the left side is known, and it is sufficient to deduce the value of the whole expression.

Let's make use of the boolean logical operators in an example, consider the example shown below:

false true false

They work only on integer variables having bit-patterns of equal length . %b is the format string for bit-representations.

The table shown below mentions the different types of bitwise operators that are present in Go.

Out of all the bitwise operators that are mentioned above, the Bitwise AND, OR, XOR and CLEAR are binary operators which means they require two operands to work on. However, the COMPLEMENT operator is a unary operator.

Now let's consider an example where we will make use of these bitwise operators in a Go program,

Operator Precedence in Go

In Programming, the concept of operator precedence is used to determine the grouping of terms in an expression. It basically affects how an expression is evaluated. There are some operators that will have higher precedence than others, for example, the division operator has higher precedence over the addition operator.

A table is shown below, that depicts how the associativity of different operators is evaluated in Go.

In the above article, we learned bout the different types of operators that are present in Go, from simple arithmetic operators to a little complicated logical operator and to the most complex bitwise operators. We also learned about their use cases and saw different examples of each of these operators.

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Golang Tutorial #6
Golang Operators
Operators and Types of Operators in Go (Golang)
Go Tutorial (Golang) 6

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#20 Assignment Operators in C#
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Go Assignment Operators
Assignment operators are used to assign values to variables. In the example below, we use the assignment operator (=) to assign the value 10 to a variable called x: Example. package main import ("fmt") func main() { var x = 10 fmt.Println(x)}
syntax
A short variable declaration uses the syntax: ShortVarDecl = IdentifierList ":=" ExpressionList . It is a shorthand for a regular variable declaration with initializer expressions but no types: "var" IdentifierList = ExpressionList . Assignments. Assignment = ExpressionList assign_op ExpressionList . assign_op = [ add_op | mul_op ] "=" .
Golang := Vs = Exploring Assignment Operators In Go
The assignment operator, =, in Go, is used to assign values to already declared variables. Unlike :=, it does not declare a new variable but modifies the value of an existing one. For example: var age int age = 30. Here, age is first declared as an integer, and then 30 is assigned to it using =.
The Go Programming Language Specification
The shift operators shift the left operand by the shift count specified by the right operand, which must be non-negative. If the shift count is negative at run time, a run-time panic occurs. The shift operators implement arithmetic shifts if the left operand is a signed integer and logical shifts if it is an unsigned integer.
Go
The following table lists all the assignment operators supported by Go language −. Operator. Description. Example. =. Simple assignment operator, Assigns values from right side operands to left side operand. C = A + B will assign value of A + B into C. +=. Add AND assignment operator, It adds right operand to the left operand and assign the ...
A Tour of Go
Inside a function, the := short assignment statement can be used in place of a var declaration with implicit type. Outside a function, every statement begins with a keyword ( var, func, and so on) and so the := construct is not available. < 10/17 >. short-variable-declarations.go Syntax Imports.
Go Operators (With Examples)
In Go, we can also use an assignment operator together with an arithmetic operator. For example, number := 2 number += 6. Here, += is additional assignment operator. It first adds 6 to the value of number (2) and assigns the final result (8) to number. Here's a list of various compound assignment operators available in Golang.
Go Assignment Operators
All the other assignment operators are built off of it. For example, the below code assigns the variable a the value of 3, the constant pi the value of 3.14, and the variable website the value of Learnmonkey: var a = 3 const pi = 3.14 var website = "Learnmonkey". Notice that we can use the assignment operator to make constants and variables.
Golang Tutorial #3
This golang tutorial discusses the use of the assignment expression operator and the difference between an implicit and explicit variable declaration. Playli...
How To Do Math in Go with Operators
Go has a compound assignment operator for each of the arithmetic operators discussed in this tutorial. To add then assign the value: y += 1. To subtract then assign the value: ... (or GoLang) is a modern programming language originally developed by Google that uses high-level syntax similar to scripting languages. It is popular for its minimal ...
Golang: Operators
We will be exploring the basics of operators and the various types like Arithmetic, Bitwise, Comparison, Assignment operators in Golang. Operators are quite fundamentals in any programming language. Operators are basically expressions or a set of character(s) to perform certain fundamental tasks. They allow us to perform certain trivial ...
Go operators
The operators of an expression indicate which operations to apply to the operands. The order of evaluation of operators in an expression is determined by the precedence and associativity of the operators. An operator usually has one or two operands. Those operators that work with only one operand are called unary operators .
Go
Go supports a number of different operators. These are symbols that modify the value of one or more expressions. These symbols include arithmetic operators, comparison operators, logical operators, bitwise operators, and assignment operators. Arithmetic Operators. Arithmetic operators take one or two numeric expressions and return a numeric result.
7 Types of Golang Operators
An operator is a symbol that tells the compiler to perform certain actions. The following lists describe the different operators used in Golang. Arithmetic Operators. Assignment Operators. Comparison Operators. Logical Operators. Bitwise Operators.
Operators In Go
In this video we'll learn about the main operators in Golang.We'll look at math operators (arithmetic operators), assignment operators, and comparison operat...
Go Operators
Different types of assignment operators are shown below: "="(Simple Assignment): This is the simplest assignment operator. This operator is used to assign the value on the right to the variable on the left. "+="(Add Assignment): This operator is a combination of '+' and '=' operators. This operator first adds the current value ...
Go lang Operators: Arithmetic, Comparison, Logical, Bitwise, Assignment
Assignment Operators. The assignment operators are used to assign literal values or assign values by performing some arithmetic operation using arithmetic operators. The following example demonstrates the assignment operators. import "fmt" func main() {. x, y := 10, 20 //Assign. x = y. fmt.Println(" = ", x) //output: 20 // Add and assign. x = 15.
Golang Assignment Operators
These operators assign the result of the right-side expression to the left-side variable or constant. The "=" is an assignment operator. Assignment operators can also be the combinations of some other operators (+, -, *, /, %, etc.) and "=". Such operators are known as compound assignment operators. List of Golang Assignment Operators
Learn Golang Operators Guide with examples
#Golang Assignment Operators; #Golang Address Operators; #Golang Operator Precedence # Go Language Operators. Like many programming languages, Golang has support for various inbuilt operators. Important keynotes of operators in the Go language. Operators are character sequences used to execute some operations on a given operand(s)
What is the difference between = and <- in golang
The = operator deals with variable assignment as in most languages. It expresses the idea of wanting to update the value that an identifier references. The <-operator represents the idea of passing a value from a channel to a reference. If you think of the channel as a queue using an assignment operator = would assign the reference to the queue to the target variable.
The Go Programming Language Specification
An assignment operation x op= y where op is a binary arithmetic operator is equivalent to x = x op (y) but evaluates x only once. The op= construct is a single token. In assignment operations, both the left- and right-hand expression lists must contain exactly one single-valued expression, and the left-hand expression must not be the blank ...
Go Operators
Go Operators. An Operator is a symbol that is used to perform logical or mathematical tasks. Go provides us different types of built-in operators, these mainly are: Arithmetic Operators. Assignment Operators. Relational Operators. Logical Operators. Bitwise Operators. In this tutorial, we will explore all the built-in operators that Go provides us.

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