Golang: Function

Function Syntax

func fname(param1 type1, param2 type2, etc) returnType {body}

package main

import "fmt"

func ff(x int, y int) int {
	return x + y
}

func main() {
	fmt.Println(ff(3, 4)) // 7
}

Return Nothing

if the function does not need a return value, simply omit the return type.

package main

import "fmt"

func ff(x int, y int) {
	fmt.Printf("%v\n", x+y)
}

func main() {
	ff(3, 4)
	// 7
}

Omit Type Spec in Parameters

Type spec can be omitted when they are the same as the last var's type.

Examples:

Following are equivalent:

func f(x, y, z int)

func f(x int, y int, z int)

Following are equivalent:

func f(x, y string, z int)

func f(x string, y string, z int)

Return Variable Syntax Shortcut

function return spec can contain variable names.

func fname(params) (name type) {body}

The name, is shothand for declaring the variable at the top of the function body.

For example, following are equivalent:

func f(x int) int { var r = x + 1; return r }

func f(x int) (r int) { r = x + 1; return r }

package main

import "fmt"

func gg(n int) (m int) {
	m = n + 1
	return m
}

func main() {
	fmt.Println(gg(5))
}

// 6

Function is a Value

Function is a value. It can be assigned to a variable, passed as argument to a function, or returned by a function.

Example:

var hh = func(x int) int { return x+1 }

package main

import "fmt"

// assign a function to a variable
var hh = func() int {
	return 3
}

func main() {
	fmt.Println(hh()) // 3
}

Apply Function to Value, Inline

Function can be applied by appending (arguments) to the function definition or name.

Example:

func(x int) int { return x + 1 }(3)

package main

import "fmt"

func main() {
	var y = func(x int) int { return x + 1 }(3)
	fmt.Println(y) // 4
}