forEach.go

package main

import "fmt"

type CB func(int, interface{})

type Array []interface{}

func (arr *Array) forEach(callback CB)  {
	for index, item := range *arr {
		callback(index, item)
	}
}

func main()  {
	strArr := &Array{"hello", "word", "word", "word", "word", 123}

	strArr.forEach(func(index int, item interface{}) {
		if value, ok := item.(string); ok {
			fmt.Printf("%d:%s\n", index, value)
		}
	})
}