#enum #future #macro #derive #implement

no-std enum_future

A simple macro for creating Future-implementing enums containing futures

1 unstable release

Uses old Rust 2015

0.1.0 Jan 28, 2019

#105 in #future

28 downloads per month

MITNFA license


enum future

A simple macro for creating Future-implementing enums containing futures.


The enum_future macro can be used as an alternative to futures::Either if more than two variants are desired or if one wants to give them more meaningful names. The enum is generic, in order to allow use with complicated or unname-able types (combinators, closures, impl Future).

This macro doesn't allow for creating pub enums, documenting them or deriving any other trait. This should be fine in most cases, as it's intended to be used mainly in match expressions returning different futures.

Derive macro would certainly provide more flexibility, but it'd also be more complicated and this simple macro solves my problem. If anyone is interested in contributing proc macro version, I'd be very happy to merge a PR!

This crate is no_std and pre-2018-compatible, since it doesn't need anything fancy from neither std nor 2018 edition.


extern crate enum_future;

use enum_future::futures::future::{Future, ok, err};

fn make_future(input: u64) -> impl Future<Item=bool, Error=&'static str> {
    enum_future!(Ret, Zero, One, Other);

    match input {
        0 => Ret::Zero(ok(false)),
        1 => Ret::One(ok(true)),
        _ => Ret::Other(err("Invalid input")),

fn main() {
    assert_eq!(make_future(42).wait(), Err("Invalid input"));