cheat.sheets/sheets/_go/func

// ### Functions
// a simple function
func functionName() {}

// function with parameters (again, types go after identifiers)
func functionName(param1 string, param2 int) {}

// multiple parameters of the same type
func functionName(param1, param2 int) {}

// return type declaration
func functionName() int {
    return 42
}

// Can return multiple values at once
func returnMulti() (int, string) {
    return 42, "foobar"
}
var x, str = returnMulti()

// Return multiple named results simply by return
func returnMulti2() (n int, s string) {
    n = 42
    s = "foobar"
    // n and s will be returned
    return
}
var x, str = returnMulti2()

// ### Functions As Values And Closures
func main() {
    // assign a function to a name
    add := func(a, b int) int {
        return a + b
    }
    // use the name to call the function
    fmt.Println(add(3, 4))
}

// Closures, lexically scoped: Functions can access values that were
// in scope when defining the function
func scope() func() int{
    outer_var := 2
    foo := func() int { return outer_var}
    return foo
}

func another_scope() func() int{
    // won't compile because outer_var and foo not defined in this scope
    outer_var = 444
    return foo
}


// Closures: don't mutate outer vars, instead redefine them!
func outer() (func() int, int) {
    outer_var := 2
    inner := func() int {
        outer_var += 99 // attempt to mutate outer_var from outer scope
        return outer_var // => 101 (but outer_var is a newly redefined
                         //         variable visible only inside inner)
    }
    return inner, outer_var // => 101, 2 (outer_var is still 2, not mutated by foo!)
}

// ### Variadic Functions
func main() {
    fmt.Println(adder(1, 2, 3))     // 6
    fmt.Println(adder(9, 9))    // 18

    nums := []int{10, 20, 30}
    fmt.Println(adder(nums...))    // 60
}
// By using ... before the type name of the last parameter you can indicate that it takes zero or more of those parameters.
// The function is invoked like any other function except we can pass as many arguments as we want.
func adder(args ...int) int {
    total := 0
    for _, v := range args { // Iterates over the arguments whatever the number.
        total += v
    }
    return total
}