list_interface.go

package main

import "fmt"

type List interface {
	ForEach(f func(v int))
}

type IntList []int

func (iL IntList) ForEach(f func(v int)) {
	for _, v := range []int(iL) {
		f(v)
	}
}

func main() {
	var iL List = IntList{1, 2, 3, 4}

	iL.ForEach(func (v int) {
		fmt.Println(v)
	})
}