functional helper

map.go

// Map is a functional map, like Kotlin or Rust map.
// wantType must be a pointer, If you want return a []*string,
// wantType should be **string
func Map(slice interface{}, wantType interface{}, f func(v interface{}) interface{}) interface{} {
	if reflect.TypeOf(slice).Kind() != reflect.Slice {
		panic("slice type must be slice")
	}

	value := reflect.ValueOf(slice)

	newType := reflect.ValueOf(wantType)

	if newType.Kind() != reflect.Ptr {
		panic("wantType must be a pointer")
	}

	newType = reflect.Indirect(newType)

	newSlice := reflect.MakeSlice(reflect.SliceOf(newType.Type()), value.Len(), value.Cap())

	for index := 0; index < value.Len(); index++ {
		v := value.Index(index)
		newSlice.Index(index).Set(reflect.ValueOf(f(v.Interface())))
	}

	return newSlice.Interface()
}