Dedenne

Cute little generators!

Dedenne implements generators, a la the unstable language feature, over async/await in completely stable Rust.

Simple Usage

use dedenne::*;

let mut generator = Generator::new(|y, init| async move {
  for x in 0..init {
    y.ield(x).await;
  }
  for x in (0..init).rev() {
    y.ield(x).await;
  }

  "All done!"
});

assert_eq!(
  generator.start(3), GeneratorResponse::Yielding(0)
);
assert_eq!(
  generator.resume(), GeneratorResponse::Yielding(1)
);
assert_eq!(
  generator.resume(), GeneratorResponse::Yielding(2)
);
assert_eq!(
  generator.resume(), GeneratorResponse::Yielding(2)
);
assert_eq!(
  generator.resume(), GeneratorResponse::Yielding(1)
);
assert_eq!(
  generator.resume(), GeneratorResponse::Yielding(0)
);
assert_eq!(
  generator.resume(), GeneratorResponse::Done("All done!")
);

For a larger example, check out this simple TUI interface.

panic! vs unreachable!

If something in Dedenne panic!s, then it's a user error. Make sure to await your y.ields, and don't call resume after a generator's exhausted.

If something in Dedenne panics with an unreachable! message, then it's a problem with Dedenne. Please file a bug report if it does.

Prior Art

I am not the first person to have this idea. However, I think Dedenne is the only crate that supports mapping over iterators.

• generator. Doesn't support a starting argument, which means you can't use it as a mapping iterator. Is always stackful.
• genawaiter. Has some convenience macros that make it nicer to make generators. Also lets you really tune how the generators are stored (stackful or allocating).
• Unstable lang feature. Doesn't support passing values in to a generator, afaict. Also requires nightly rust and has been bikeshedding for 6 years as of time of writing.