Promise

Go Promise Implementation with support for Generics (requires Go v1.18+).
Run async operations lazily in a separate goroutine on the fly.

Features

Easy interface for composing async operations
Executes a function in a separate goroutine
Error Handling using functions (also executed in a separate goroutine)
Support for Generics (requires Go v1.18+)
Promises are resolved lazily, upon a first call to Await, AwaitOr, Then, OnSuccess or onFailure
Support for promise.All and promise.Race (equivalent to the JavaScript Promise object)

Quickstart

package main

import (
	"log"
	"net/http"

	"github.com/felix-kaestner/promise"
)

func main() {
    // Create a new promise.
    // In this example the http request is executed in a separate goroutine
    p := promise.New(func() (*http.Response, error) {
        return http.Get("https://jsonplaceholder.typicode.com/posts/1")
    })
    
    // Handle successful and failed operations in a separate goroutine
    p.Then(func(res *http.Response) {
        log.Printf("Status: %s", res.Status)
    }, func(err error) {
        log.Fatalln(err)
    })

    // Handle only successful operations in a separate goroutine
    p.onSuccess(func(res *http.Response) {
        log.Printf("Status: %s", res.Status)
    })

    // Handle only failed operations in a separate goroutine
    p.onFailure(func(err error) {
        log.Fatalln(err)
    })

    // Await the promise.
    // This blocks execution until the promise is resolved.
    res, err := p.Await()
    
    // Provide a default value (calls Await() internally).
    res = p.AwaitOr(nil)

    // Use channels to select the awaited promise 
    select {
    case <-p.Done():
        res, err = p.Await() // returns immediately since the promise is already resolved
    case <-time.After(5000 * time.Millisecond):
        fmt.Println("Timeout")
    }

    // Take multiple promises and wait for all of them to be finished
    p1 := promise.New(func() (*http.Response, error) {
        return http.Get("https://jsonplaceholder.typicode.com/posts/1")
    })
    p2 := promise.New(func() (*http.Response, error) {
        return http.Get("https://jsonplaceholder.typicode.com/posts/2")
    })
    res, err := promise.All(p1, p2).Await()

    // Take multiple promises and wait until the first of them to is finished
    p1 := promise.New(func() (*http.Response, error) {
        return http.Get("https://jsonplaceholder.typicode.com/posts/3")
    })
    p2 := promise.New(func() (*http.Response, error) {
        return http.Get("https://jsonplaceholder.typicode.com/posts/4")
    })
    res, err := promise.Race(p1, p2).Await()

}

Installation

Install with the go get command:

$ go get -u github.com/felix-kaestner/promise

Contribute

All contributions in any form are welcome! 🙌🏻
Just use the Issue and Pull Request templates and I'll be happy to review your suggestions. 👍

Released under the MIT License.