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#1862 in Asynchronous

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Apache-2.0 OR MIT

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Build License Cargo Documentation

Macros for using smol-rs.

One of the advantages of smol is that it lets you set up your own executor, optimized for your own use cases. However, quick scaffolding is important for many organizational use cases. Especially when sane defaults are appreciated, setting up your own executor is a waste of time.

This crate provides macros for setting up an efficient smol runtime quickly and effectively. It provides sane defaults that are useful for most applications.

Simple Executor

Just have an async main function, using the main macro.

use smol_macros::main;

main! {
    async fn main() {
        println!("Hello, world!");

This crate uses declarative macros rather than procedural macros, in order to avoid needing to use heavy macro dependencies. If you want to use the proc macro syntax, you can use the macro_rules_attribute::apply function to emulate it.

The following is equivalent to the previous example.

use macro_rules_attribute::apply;
use smol_macros::main;

async fn main() {
    println!("Hello, world!");

Task-Based Executor

This crate re-exports smol::Executor. If that is used as the first parameter in a function in main, it will automatically create the executor.

use macro_rules_attribute::apply;
use smol_macros::{main, Executor};

async fn main(ex: &Executor<'_>) {
    ex.spawn(async { println!("Hello world!"); }).await;

If the thread-safe smol::Executor is used here, a thread pool will be spawned to run the executor on multiple threads. For the thread-unsafe smol::LocalExecutor, no threads will be spawned.

See documentation for the main function for more details.


Use the test macro to set up test cases that run self-contained executors.

use macro_rules_attribute::apply;
use smol_macros::{test, Executor};

async fn do_test(ex: &Executor<'_>) {
    ex.spawn(async {
        assert_eq!(1 + 1, 2);

MSRV Policy

The Minimum Supported Rust Version (MSRV) of this crate is 1.63. As a tentative policy, the MSRV will not advance past the current Rust version provided by Debian Stable. At the time of writing, this version of Rust is 1.63. However, the MSRV may be advanced further in the event of a major ecosystem shift or a security vulnerability.


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.


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