A short note on async Rust

I procrastinated for years on figuring out what the deal with async Rust is. Here's what I wish I'd gotten to read right away.

There is exactly one "magical" bit involved with async Rust and that's marking a function async and calling await from inside the async function. This will compile the body of the function into an anonymous state machine type that implements the Future trait. Calling an async function produces a Future value that implements the state machine for the function's body. It must be polled to run the function code. When the function's future is being executed via polling, an await call in the function code can suspend the execution, and it can then be resumed later with a new poll.

The rest of how an async program works can be figured out in terms of regular Rust syntax and the various library types involved.