Explore `async_fn_traits`

[Xuanwo]

pub trait AsyncFnMut<Args>: AsyncFnOnce<Args>
where
    Args: Tuple,
{
    type CallRefFuture<'a>: Future<Output = Self::Output>
       where Self: 'a;

    // Required method
    extern "rust-call" fn async_call_mut(
        &mut self,
        args: Args,
    ) -> Self::CallRefFuture<'_>;
}

AsyncFnMut is the async version of FnMut. With tuple_traits and async_fn_traits, maybe we can retry a function with args.

[Xuanwo]

backon/src/async_retry.rs

Lines 60 to 70 in d25a913

	impl<'a, B, T, E, Args, FutureFn> Retryable<'a, B, T, E, Args, FutureFn> for FutureFn
	where
	B: BackoffBuilder,
	Args: Tuple,
	FutureFn: AsyncFnMut<Args, Output = Result<T, E>> + 'a,
	{
	fn retry(self, builder: &B, args: Args) -> Retry<'a, B::Backoff, T, E, Args, FutureFn> {
	Retry::new(self, builder.build(), args)
	}
	}

Doesn't work as expected.

[Xuanwo]

See #183