Use ControlFlow for IDLE callback return type #194
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It's available on nightly if anyone wants to try an experiment to see what it would look like: https://doc.rust-lang.org/nightly/std/ops/enum.ControlFlow.html (I agree with waiting for it to stabilize before merging such a change, though.) EDIT: And I have a PR up to stabilize it, though libs has yet to weigh in. |
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It just missed 1.54, but |
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…m-basics, r=m-ou-se Stabilize `ops::ControlFlow` (just the type) Tracking issue: rust-lang#75744 (which also tracks items *not* closed by this PR). With the new `?` desugar implemented, [it's no longer possible to mix `Result` and `ControlFlow`](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=13feec97f5c96a9d791d97f7de2d49a6). (At the time of making this PR, godbolt was still on the 2021-05-01 nightly, where you can see that [the mixing example compiled](https://rust.godbolt.org/z/13Ke54j16).) That resolves the only blocker I know of, so I'd like to propose that `ControlFlow` be considered for stabilization. Its basic existence was part of rust-lang/rfcs#3058, where it got a bunch of positive comments (examples [1](rust-lang/rfcs#3058 (comment)) [2](rust-lang/rfcs#3058 (review)) [3](rust-lang/rfcs#3058 (comment)) [4](rust-lang/rfcs#3058 (comment))). Its use in the compiler has been well received (rust-lang#78182 (comment)), and there are ecosystem updates interested in using it (rust-itertools/itertools#469 (comment), jonhoo/rust-imap#194). As this will need an FCP, picking a libs member manually: r? `@m-ou-se` ## Stabilized APIs ```rust #[derive(Debug, Clone, Copy, PartialEq)] pub enum ControlFlow<B, C = ()> { /// Exit the operation without running subsequent phases. Break(B), /// Move on to the next phase of the operation as normal. Continue(C), } ``` As well as using `?` on a `ControlFlow<B, _>` in a function returning `ControlFlow<B, _>`. (Note, in particular, that there's no `From::from`-conversion on the `Break` value, the way there is for `Err`s.) ## Existing APIs *not* stabilized here All the associated methods and constants: `break_value`, `is_continue`, `map_break`, [`CONTINUE`](https://doc.rust-lang.org/nightly/std/ops/enum.ControlFlow.html#associatedconstant.CONTINUE), etc. Some of the existing methods in nightly seem reasonable, some seem like they should be removed, and some need more discussion to decide. But none of them are *essential*, so [as in the RFC](https://rust-lang.github.io/rfcs/3058-try-trait-v2.html#methods-on-controlflow), they're all omitted from this PR. They can be considered separately later, as further usage demonstrates which are important.
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The the
ControlFlowtype might be nicer than thebooltype as a return for the IDLE callbacks. If / when the type is stabilized have a look at implementing it there.Originally posted by @jonhoo in #186 (comment)
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