`distinct` op

[hunshenshi]

distinct always works with the operations window or group, the return value is a unique key.

example code:

// rxgo.Just(1, 2, 2, 3, 1, 4, 4, 5, 6, 4)().Distinct(distinct)

func distinct(_ context.Context, item interface{}) (interface{}, error) {
	// 1.Serialize
	b, err := json.Marshal(item.V.(models.Customer))
	if err != nil {
		l.Error(err)
	}

	// 2.Invoke wasm code
	code := ins.HandleEvent(ctx, "distinct", b).Code
	l.Info(fmt.Sprintf("distinct wasm code %d", code))

	// 3.Get & parse data
	if code < 0 {
		l.Error(errors.New(fmt.Sprintf("%v %s error.", item.V.(models.Customer), "distinct")))
		//TODO handle exceptions
		return "error"
	}

	rb, ok := ins.GetResource(uint32(code))
	defer ins.RmvResource(ctx, uint32(code))
	if !ok {
		l.Error(errors.New("groupByAge result not found"))
		//TODO handle exceptions
		return "error"
	}

	distinct := string(rb)
	return distinct
}