async_fn_traits - The Rust Unstable Book

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# `async_fn_traits`

See Also: `fn_traits`

The `async_fn_traits` feature allows for implementation of the `AsyncFn*` traits for creating custom closure-like types that return futures.

The main difference to the `Fn*` family of traits is that `AsyncFn` can return a future that borrows from itself (`FnOnce::Output` has no lifetime parameters, while `AsyncFnMut::CallRefFuture` does).