/// Yields a value from a generator.
///
/// This macro can only be used inside the `gen!` and `producer!` families of
/// macros.
///
/// It will suspend execution of the function until the generator is resumed. At
/// that time, it will evaluate to the resume argument, if given, otherwise it
/// will evaluate to `()`.
///
/// # Examples
///
/// [_See the module-level docs for examples._](.)
// Internal use only. This is a copy of `futures::pin_mut!` so we can avoid
// pulling in a dependency for a two-liner.