Golang: Variables

By Xah Lee. Date: . Last updated: .
var name type
Declare a variable.
var name2, name2, name3 type
Delare variables name1 etc, all of type type.
package main

import "fmt"

var x int
var y float32
var z string

var a, b, c int

func main() {
	fmt.Printf("%#v %#v %#v\n", x, y, z) // 0 0 ""
	// the %#v means show in golang syntax. else, empty string won't be displayed

	fmt.Printf("%#v %#v %#v\n", a, b, c) // 0 0 0
}

Default Value (Zero Value)

When variable is declared but not assigned a value yet, it gets its default value. Different type of value has different default values. The default values are called “zero value” [see Golang: Zero Value]

For int type, default is 0.

Variable with Value

A var declaration can also have value. (golang calls this “initialization”.)

var x = 3

If given a value, then its “type” can be omitted in the declaration. Golang will infer the type.

package main

import "fmt"

func main() {

	// var declaration, with assignment
	var x = 3
	// no type. golang can infer the type

	fmt.Println(x) // 3

	// print its type
	fmt.Printf("%T\n", x) // int
}

Parallel Assignment

var x, y, z = 3, 4, 1
Declare and assign multiple variables.
package main

import "fmt"

func main() {
	var x, y = 3, 4
	fmt.Println(x, y) // 3 4
}

Note: it's common to see the following, when a function return multiple values.

var x, y = f(3)

[see Golang: Function]

Variable Scope

package main

import "fmt"

// package level variable
var x = 3

func main() {
	// function level variable
	var y = 4

	fmt.Println(x, y) // 3 4
}

Variable Syntax Shortcut Inside Function

Inside a function, the syntax

name := val

is the same as

var name = val

[see Golang: Function]

package main

import "fmt"

func main() {
	k := 3
	fmt.Println(k)
}

// 3

Grouping Variable Declaration

Alternative syntax for variable is to have var only appear once, like this:

var (name1 type1; name1 type2 etc)

or

var (name1 = val1; name2 = val2 etc)

package main

import "fmt"

var (
	a int
	b = 2
	c = "some"
	d int
)

func main() {
	fmt.Println(a, b, c, d) // 0 2 some 0
}

Note: Semicolon ; is optional when it is at end of line.

Reference

The Go Programming Language Specification - The Go Programming Language#Variables

Golang

Examples

Reference