A simple function that does not accept any parameters and does not return any values:

func SayHello() {
    fmt.Println("Hello!")
}

A function can optionally declare a set of parameters:

func SayHelloToMe(firstName, lastName string, age int) {
    fmt.Printf("Hello, %s %s!\n", firstName, lastName)
    fmt.Printf("You are %d", age)
}

Notice that the type for firstName is omitted because it is identical to lastName.

A function can return one or more values to the caller:

func AddAndMultiply(a, b int) (int, int) {
    return a+b, a*b
}

The second return value can also be the error var :

import errors

func Divide(dividend, divisor int) (int, error) {
    if divisor == 0 {
        return 0, errors.New("Division by zero forbidden")
    }
    return dividend / divisor, nil
}

Two important things must be noted:

• The parenthesis may be omitted for a single return value.
• Each return statement must provide a value for all declared return values.

Return values can be assigned to a local variable. An empty return statement can then be used to return their current values. This is known as "naked" return. Naked return statements should be used only in short functions as they harm readability in longer functions:

func Inverse(v float32) (reciprocal float32) {
    if v == 0 {
        return
    }
    reciprocal = 1 / v
    return
}

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//A function can also return multiple values
func split(sum int) (x, y int) {
    x = sum * 4 / 9
    y = sum - x
    return
}

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Two important things must be noted:

• The parenthesis around the return values are mandatory.
• An empty return statement must always be provided.

A simple literal function, printing Hello! to stdout:

package main

import "fmt"

func main() {
    func(){
        fmt.Println("Hello!")
    }()
}

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---

A literal function, printing the str argument to stdout:

package main

import "fmt"

func main() {
    func(str string) {
        fmt.Println(str)
    }("Hello!")
}

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---

A literal function, closing over the variable str:

package main

import "fmt"

func main() {
    str := "Hello!"
    func() {
        fmt.Println(str)
    }()
}

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---

It is possible to assign a literal function to a variable:

package main

import (
    "fmt"
)

func main() {
    str := "Hello!"
    anon := func() {
        fmt.Println(str)
    }
    anon()
}

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A variadic function can be called with any number of trailing arguments. Those elements are stored in a slice.

package main

import "fmt"

func variadic(strs ...string) {
     // strs is a slice of string
     for i, str := range strs {
         fmt.Printf("%d: %s\n", i, str)
     }
}

func main() {
     variadic("Hello", "Goodbye")
     variadic("Str1", "Str2", "Str3")
}

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You can also give a slice to a variadic function, with ...:

func main() {
     strs := []string {"Str1", "Str2", "Str3"}

     variadic(strs...)
}

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