FAQ.md

FAQ

What async runtime is the best?

There are many to choose from and if they have a certain maturity, the performance differences should be negligible (for this project, anyway).
What remains are two major things to consider: compatibility to other frameworks and API stability/maintenance.
The former is important because some other libraries come with hard dependencies on - for example - tokio, so if you picked Bastion, you’d end up with two async executors and potentially strange side effects.
Both are personal or project specific choices - and for this project it is highly recommended to use async-std, which provides an abstraction layer over several runtimes (incl. its own runtime).

Note: Since the crate hyper requires the tokio runtime, this project uses tokio from within async-std.

Is there a specific edition/version of Rust I should use?

You should use the latest version of Rust whenever possible.

What are the advantages in making traits async?

Traits can be used as interfaces to provide a production and a testing implementation of something (for example) - and for modern Rust, this interface can require async functions.

Until Rust 1.75 async traits were not supported out of the box and required using an additional crate: async_trait.

As of Rust 1.75, async traits are supported (see Rust Blog).

I’m used to seeing async calls on blocking operations as network or database queries, not regular processing. Does Rust async code make better usage of multi-core processors?

CPU-bound applications typically don’t benefit from async, although the runtime could be multithreaded across different cores.
crossbeam or other crates help with effective parallel processing.
Tasks that benefit from async are usually I/O bound and require lots of waiting, such as network or disk I/O.
In the case of this project (series) the calculations are light and using async to schedule them on a loop can increase efficiency since we are frequently doing a lot of them, so our cores won’t be idle or overloaded.

If you are considering some heavier processing, check out crossbeam or other crates that provide parallelization features.

How can I test async code?

Tests require, just as regular code, a runtime to schedule and execute futures.
As async functions, the return type will always be a Future type, thus the test runner (cargo in this case) has to be able to execute those.
Use an attribute such as tokio::test, or async_std::test from the framework of your choosing (async-std being the default).