From Java to Go, and Back Again (2016)(opencredo.com)

  func mapThingToThing(inSlice interface{}, mapperFn interface{}) []interface{} {
  	mapper := reflect.ValueOf(mapperFn)
  	input := reflect.ValueOf(inSlice)
  	output := make([]interface{}, input.Len())
  	for i := 0; i < input.Len(); i++ {
  		item := input.Index(i)
  		output[i] = mapper.Call([]reflect.Value{item})[0]
  	}
  	return output
  }

  fn := func(item string) string {
  	return item + "!"
  }
  res := mapThingToThing([]string{"a", "b", "c"}, fn)
  for _, item := range res {
  	fmt.Printf("item = %+v\n", item)
  }

    f, err := os.Open("somefile")
    ...
    http.ServeContent(w, r, "", time.Now(), f)

    func Splice(
        src io.ReadSeeker, 
        splice map[time.Duration]io.ReadSeeker,
    ) (io.ReadSeeker, error)

    f1, _ := os.Open("/tmp/1.mp3")
    f2, _ := os.Open("/tmp/2.mp3")
    f3, _ := os.Open("/tmp/3.mp3")
    final, _ := mp3.Splice(f1, map[time.Duration]io.ReadSeeker{
        time.Second * 5:  f2,
        time.Second * 10: f3,
    })

    func NewMultiReadSeeker(
        readSeekers ...io.ReadSeeker,
    ) io.ReadSeeker

    func NewSectionReadSeeker(
        src io.ReadSeeker, 
        offset, length int64,
    ) io.ReadSeeker

    final := NewMultiReadSeeker(
        NewSectionReadSeeker(f1, 0, A),
        f2,
        NewSectionReadSeeker(f1, A, B-A),
        f3,
        NewSectionReadSeeker(f1, B, C-B),
    )