#promise #javascript #async #futures


Effective, simple, lightweight Javascript promises in Rust

2 unstable releases

Uses old Rust 2015

0.2.0 Mar 28, 2016
0.1.0 Mar 28, 2016

#9 in #promise

MIT license

220 lines


This library seeks to fully, effectively and simply recreate lightweight Javascript-style promises in Rust.

rust-promises offers all the features of Ecmascript 6 promises plus a few Rust methods from Result<T, E>, implemented using the std::thread API and Rust's asyncronous Sender and Receiver.


TODO (after adding some Result methods to Promise).


Promises are an excellent building block for asyncronous programming. They're a great way to build an asyncronous library, and also a small dependency for existing code.

Javascript's promises were adapted from promises in a programming language called E, which has a very powerful distributed computing architecture using message passing.

Rust's std::sync::mpsc::{Sender, Receiver} provide a way to build such an architecture (and promises) from Rust's safe threading systems.

Oh great, another promise library

There are currently 5 asyncronous libraries on crates.io which offer promises or futures. However they all have problems:

  • They are all in beta and unstable, with versions < 0.5 (like this library right now...)
  • Some of them are larger async libraries. They require programming within event loops, or are designed for specific scenarios. If you want a whole async library for a specific type of programming, go use those.
  • The rest are variations on the promise concept, i.e. returning a (Future, Promise) pair from Promise::new(). If you know how to use that, go to those libraries, I guess.

No runtime deps