Function types and values

Function types and function values can be used and passed around just like other values:

type Operator func(x float64) float64

// Map applies op to each element of a.
func Map(op Operator, a []float64) []float64 {
    res := make([]float64, len(a))
    for i, x := range a {
        res[i] = op(x)
    return res

func main() {
    op := math.Abs
    a := []float64{1, -2}
    b := Map(op, a)
    fmt.Println(b) // [1 2]

    c := Map(func(x float64) float64 { return 10 * x }, b)
    fmt.Println(c) // [10, 20]

The second call to Map uses a function literal (or lambda). See Anonymous functions and closures for more about lambdas in Go.


A function type describes the set of all functions with the same parameter and result types.

The following two function types are identical.

func(x, y int) int
func(int, int) int

Further reading

Anonymous functions and closures

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