Promises implementation using Go (Golang)

promises_example.go

package main

import (
	"errors"
	"fmt"
)

type Promise struct {
	successChannel chan interface{}
	failureChannel chan error
}

type Message struct {
	ID    int
	Value float64
}



func main() {
	msg1 := new(Message)
	msg1.ID = 2
	msg1.Value = 123.12318123
	SaveMessage(msg1).Then(func(obj interface{}) error {
		msg1 := obj.(*Message)
		fmt.Printf("Message %d", msg1.ID)
		return nil
	}, func(err error) {
		fmt.Printf("Error: " + err.Error())
	})

	fmt.Scanln()
}

// SaveMessage -> receieve a pointer to a message and returns a promise
func SaveMessage(msg *Message) *Promise {
	result := new(Promise)

	result.successChannel = make(chan interface{}, 1)
	result.failureChannel = make(chan error, 1)

	go func() {
		if msg.ID%2 == 0 {
			result.failureChannel <- errors.New("Fail to save message")
		} else {
			result.successChannel <- msg
		}
	}()

	return result
}


func (this *Promise) Then(success func(interface{}) error, failure func(error)) *Promise {

	result := new(Promise)

	result.successChannel = make(chan interface{}, 1)
	result.failureChannel = make(chan error, 1)

	go func() {
		select {
		case obj := <-this.successChannel:
			newErr := success(obj)
			if newErr != nil {
				result.failureChannel <- newErr
			} else {
				result.successChannel <- obj
			}
		case err := <-this.failureChannel:
			failure(err)
			result.failureChannel <- err
		}
	}()

	return result
}