Var

The var keyword in Go is used to declare variables. These can be done outside a function (and can be used throughout a program) or inside a function.

Similar to the const keyword, var can be used to group together several declarations. And it can replace uses of the new() built-in function.

Example

We can declare variables in a var block. Here variables are initialized at runtime, and they can be reassigned in methods. They can be used throughout the program.

Part 1 Here we use a var declaration that is at the file scope, and not part of any function body.

Part 2 We can change the value of the file-level var within a func. This value is available in all funcs in a file.

Part 3 We can group vars together. This reduces some syntax and can make programs be easier to read.

Part 4 We can use var in place of the new() built-in. New() returns a pointer, while var returns the actual object data.

package main

import "fmt"

// Part 1: use global var.
var position int

func main() {
    // Part 2: adjust global var value.
    position = 10
    fmt.Println("Test1:", position)
    position = 20
    fmt.Println("Test2:", position)

    // Part 3: use local var with single var block.
    var (
        color = "blue"
        size  = 10
    )
    fmt.Println("Color and size:", color, size)

    // Part 4: use var and new to allocate an int.
    var x int = 100
    y := new(int)
    *y = 100
    fmt.Println(x, *y)
}Test1: 10
Test2: 20
Color and size: blue 10
100 100

Var, `short` syntax

We can use the var keyword with a type or without a type. We can declare variables with var, but it is also possible to use a shorter syntax.

Version 1 This code uses a var declaration with no type specified. The string is assigned to different values and printed.

Version 2 This version uses a short variable declaration—it does the same thing as program version 1.

package main

import "fmt"

func Test1() {
    // Version 1: use a local variable string.
    var animal = "Cat"
    fmt.Println("TEST1: " + animal)
    // Reassign the local variable.
    animal = "Dog"
    fmt.Println("TEST1: " + animal)
}

func Test2() {
    // Version 2: use short variable declaration.
    animal := "Cat"
    fmt.Println("TEST2: " + animal)
    // Reassign it.
    animal = "Dog"
    fmt.Println("TEST2: " + animal)
}

func main() {
    Test1()
    Test2()
}TEST1: Cat
TEST1: Dog
TEST2: Cat
TEST2: Dog

Typed vars

A var declaration can have more than one variable in it, and each can have a separate value. But only one type can be used. All variables use the specified type.

package main

import "fmt"

func main() {
    // Create two vars of type int32 on one line.
    var n, y int32 = 100, 200
    // Display variables.
    fmt.Println(n)
    fmt.Println(y)
}100
200

Var is used throughout Go programs to declare variables. It can be used inside, and outside of, functions—and it can group together related variables.

Var

Example

Var, short syntax

Typed vars

Var, `short` syntax