Promise

Initially this started out as an experiment to better understand the inner workings of JavaScript promises and how this can be implemented from scratch in go.

The result is a promise implementation which follows the Promises/A+ Standard and comes with the following additional features:

• Waiting for promise resolution.
• Panics during promise resolution cause the promise to be rejected with the panic message.
• Nested promise resolution.
• Race, All, Any and AllSettled extensions to handle the parallel resolution of multiple promises.
• Promise pooling. See the promise.Pool documentation and the pooling example.
• Promise instrumentation for tracing, logging and debugging. See the instrumented package documentation for more information.

Head over to the promise godoc for the API documentation.

Installation

go get -u github.com/martinohmann/promise

Usage

Check out the examples in the _examples/ directory to see promises in action.

Simple example

package main

import (
	"errors"
	"fmt"
	"math/rand"
	"time"

	"github.com/martinohmann/promise"
)

func init() {
	rand.Seed(time.Now().UnixNano())
}

func main() {
	p := promise.New(func(resolve promise.ResolveFunc, reject promise.RejectFunc) {
		// simulate some computation
		sleepDuration := time.Duration(rand.Int63n(2000)) * time.Millisecond
		time.Sleep(sleepDuration)

		fmt.Printf("computation took %s\n", sleepDuration)

		// inject some random errors
		if rand.Int63n(2) == 0 {
			reject(errors.New("computation failed"))
			return
		}

		// simulate computation result
		resolve(rand.Int63())
	}).Then(func(val promise.Value) promise.Value {
		fmt.Printf("computation result: %d\n", val.(int64))
		return val
	}).Catch(func(err error) promise.Value {
		fmt.Printf("error during computation: %v\n", err)
		return err
	})

	// Wait for the promise resolution to be complete, that is: either fulfillment or rejection.
	val, err := p.Await()
	if err != nil {
		fmt.Printf("Promise rejected with error: %v\n", err)
	} else {
		fmt.Printf("Promise fulfilled with value: %d\n", val.(int64))
	}
}

License

The source code of promise is released under the MIT License. See the bundled LICENSE file for details.