iwantcoding.com
🔥 Daily 👥 Rooms 🏆 Top Log in Sign up

Functions

By · Reviewed & last updated · Part of Go Tutorial

Go functions are first-class: pass them as values, return them, store them in struct fields. Multiple returns + named returns are common. Defer runs on function exit — ideal for cleanup.

Multi-return, named returns, closures, defer

EXAMPLE
package main

import (
    "errors"
    "fmt"
    "os"
)

// Multiple returns — the (T, error) idiom
func divide(a, b int) (int, error) {
    if b == 0 {
        return 0, errors.New("divide by zero")
    }
    return a / b, nil
}

// Named returns — pre-declared, can be set without listing them
func bounds(xs []int) (min, max int, err error) {
    if len(xs) == 0 {
        err = errors.New("empty")
        return
    }
    min, max = xs[0], xs[0]
    for _, x := range xs {
        if x < min { min = x }
        if x > max { max = x }
    }
    return
}

// Variadic — last param accepts any number of values
func sum(xs ...int) int {
    total := 0
    for _, x := range xs { total += x }
    return total
}

// Closures — capture surrounding variables
func counter() func() int {
    n := 0
    return func() int { n++; return n }
}

// Defer — runs at function exit (LIFO)
func writeFile(path string) error {
    f, err := os.Create(path)
    if err != nil { return err }
    defer f.Close()                  // guaranteed close, even on panic

    _, err = f.WriteString("hello")
    return err
}

func main() {
    q, _ := divide(17, 5)
    fmt.Println(q, sum(1, 2, 3, 4))

    next := counter()
    fmt.Println(next(), next(), next())
}

Why it matters

defer + (T, error) + checking err != nil is the rhythm of every Go program. Internalise it and idiomatic Go writes itself.

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

Example

Example
func add(a, b int) int { return a + b }

func divmod(a, b int) (int, int) { return a/b, a%b }

q, r := divmod(17, 5)
Try it Yourself »

Exercise

Return type for a function adding two ints.

func add(a, b int) { return a + b }

Discussion

Loading…