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Variables

By · Reviewed & last updated · Part of Go Tutorial

Go variables come in three flavours: var (explicit), := (short declaration with inference), and const. Zero values are guaranteed: 0 for ints, \"\" for strings, nil for pointers, slices, maps, channels.

The three flavours

EXAMPLE
package main

import "fmt"

// Package-level — must use var, not :=
var (
    appName = "hello"
    version = 3
)

const MaxUsers = 1000   // compile-time constant

func main() {
    // Short declaration — only inside functions, types inferred
    name := "Ada"
    age  := 36

    // Multiple at once
    a, b := 1, 2
    a, b = b, a   // swap, no temp var

    // Explicit type
    var pi float64 = 3.14

    // Zero values — declared but not initialised
    var (
        count   int     // 0
        ok      bool    // false
        items   []int   // nil
        cache   map[string]int  // nil — cannot insert into a nil map
    )
    items = append(items, 1)        // append works on nil slices
    cache = make(map[string]int)    // must make before use

    fmt.Println(name, age, pi, a, b, count, ok, items, cache)
}

Why it matters

Unused variables are a compile error. The discipline forces tidy code — you can’t leave dead bindings lying around.

Tip: Tweak the snippet with Try it Yourself », then sit the quiz at the bottom of the page.

Example

Example
var age int = 30
name := "Ada"   // type inferred
const pi = 3.14159
Try it Yourself »

Exercise

Short variable declaration.

name "Ada"

Discussion

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