Semantic one-shot channel

[tisonkun]

Different from #199, a semantic one-shot channel may help in reasoning.

That said, bounded(1) doesn't mean the channel will handle only one event all the time, but it can buffer at most one event.

A semantic one-shot channel is like a CountDownLaunch with count=1, which means only one event can be delivered and the following will be rejected with an error.

I don't find an implementation in crossbeam-channel. Thus, I file this issue to see if it's a valid suggestion or we can implement it with current structs.

[taiki-e]

What is the actual purpose of this?

If the purpose is to restrict the API, you might be able to do this just by creating a wrapper type.

If the purpose is performance, it is not clear how large the actual performance benefit is, as I felt the single-capacity optimized variant I tried in #199 was similar to the one used in tokio::sync::oneshot.

[tisonkun]

If the purpose is to restrict the API, you might be able to do this just by creating a wrapper type.

That sounds reasonable...Do you have a demo wrapper for such usage?

[tisonkun]

I know that I can wrap a OneShotSender that has a fn send(self, ...) now.

Thanks for your well-written library for use!