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Working group dedicated to improving the foundations of Async I/O in Rust

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RFC: Return type notation

tmandry opened this issue · comments

commented

This is a roadmap item for wg-async. You can view the roadmap here: https://github.com/orgs/rust-lang/projects/28

commented

Could you add a description here?

commented

Quick comment regarding Why not make all futures send?. First time commenting a Rust RFC, so apologies if this isn't the right place to share this (it wouldn't fit in a hackmd comment :)).

I think the question "Why not put send bounds on the trait?" (as suggested in the comment) is a better one, for the following reasons.

  • async_trait does it, and users will want to migrate to the stable async trait features when it becomes available. This section will be the go-to place (at least, at first) to understand why it doesn't work the same way.

  • Traits define a contract, function signatures define a contract. These two concepts seem similar enough that users will be confused?

  • May I propose looking at this question from the perspective of different personas?

    • Async runtime makers want (...). (I don't know)

    • Library authors want to hide the complexity from their users.

    • End users want simple code (ie: simple traits and simple function signatures), and are fine with some trade-offs that are not acceptable for library authors. Making every trait Send might be fine for them? (Another example of this: code written with std not being portable to no_std)

    • Work-stealing async runtime users need Send types, and so (..). Single threaded async-runtime users can use both Send and !Send, but don't want to be restricted to Send when implementing types, etc.. (aka: could we make all futures Send, with an escape hatch?)

    I'm not sure RTN "wins" for these last 2 points, compared to Send-bound traits

  • Could we have both RTN and Send-bound traits? Is this a bad idea/impossible?

Maybe some of these could be mentioned in Drawbacks. My point is mostly that I believe this question to be important, and the first place people will read 👍