Golang: Variables

Declare Variable Without Value

var name type

Declare a variable.

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
}

var name2, name2, name3, etc type

Delare variables name1 etc, all of type type.

Default Value (Zero Value)

• Golang: Zero Value

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 Multi-Value Returns〕

Variable Scope

• Variables in a package are local to the package.
• Variables inside function are local to the function.

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 = value1; name2 = value2; 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.