select macro uses ident instead of expr

[PvdBerg1998]

Is there a safety reason for this? Otherwise it'd greatly improve user friendlyness if the macro could take an expression instead of an identifier!

[Alxandr]

Same with join (and I'm guessing try_select and try_join).

[skade]

There's no safety reasons for this, we accept patches to have macros accept a wider array of options and forms.

[yoshuawuyts]

Afaik @taiki-e tried to make this work for futures-rs as well, and they ended up having to write a proc macro. For compile-speed reasons we've chosen not to include proc macros by default in our codebase, so that wouldn't be an option for us.

In async-rs/async-std#405 we've added Future::race which should help alleviate things somewhat. I've also filed async-rs/async-std#470 to help with the most common join cases as well. Hopefully this is enough to make futures concurrency a bit nicer to work with.

Thanks!

[skade]

Geoffroy gave a hint at a slightly better version here: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=fd5313767dfa99e460c60a33d940cef8