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libcore: Add iter::from_generator which is like iter::from_fn, but for coroutines instead of functions #96298

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merged 1 commit into from
May 27, 2022

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@petrochenkov petrochenkov commented Apr 21, 2022

An equally useful little helper.

I didn't follow any of the async-wg work, so I don't know why something like this wasn't added before.

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Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with r? rust-lang/libs-api @rustbot label +T-libs-api -T-libs to request review from a libs-api team reviewer. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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@rustbot rustbot added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Apr 21, 2022
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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 21, 2022
@petrochenkov petrochenkov added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. and removed T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Apr 21, 2022
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library/core/src/iter/mod.rs Outdated Show resolved Hide resolved
library/core/src/iter/sources.rs Outdated Show resolved Hide resolved
library/core/tests/iter/sources.rs Outdated Show resolved Hide resolved
/// [`iter::from_fn`]: crate::iter::from_fn
#[inline]
#[unstable(feature = "iter_from_generator", issue = "none", reason = "generators are unstable")]
pub fn from_generator<G: Generator<Return = ()> + Unpin>(
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It might be reasonable to also add a version that accepts a Pin<&mut G>, since that way immovable generators can be used as well.

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I'm intrigued if there's a way to support both from the same function (is a Pin<&mut Generator<Return = ()>>: Generator<Return = ()> + Unpin?)

Either way, I think we can add that on a follow up PR.

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I'm not quite sure what you mean. Right now there isn't an easy way to accept both direct mutable references and pinned ones, but that would be a lovely thing.

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I'm just wondering what changes we could make so that Pin<&mut Generator<Return = ()>> can satisfy Generator<Return = ()> + Unpin, making this function work for both versions.

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Oh! Now I understand, I think. That's actually a good question...

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Pretty sure that's already the case for Future (yup) so it shouldn't be hard to do it for Generator.

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The main cases I've seen of this pattern in the wild have been via the propane crate which mostly provides exactly what this does except via a macro instead. Not sure if there are more recent uses that folks can point to, though.

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I'm r=me after addressing @jyn514's nitpicks. If we ever stabilize generators this API will likely be either redundant or changed, but while the whole feature is unstable, having these kind of affordances is important.

@petrochenkov petrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 26, 2022
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@bors r=estebank

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bors commented May 26, 2022

📌 Commit 5bf23f6 has been approved by estebank

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 26, 2022
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bors commented May 27, 2022

⌛ Testing commit 5bf23f6 with merge 4f68efa...

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bors commented May 27, 2022

☀️ Test successful - checks-actions
Approved by: estebank
Pushing 4f68efa to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label May 27, 2022
@bors bors merged commit 4f68efa into rust-lang:master May 27, 2022
@rustbot rustbot added this to the 1.63.0 milestone May 27, 2022
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Finished benchmarking commit (4f68efa): comparison url.

Instruction count

  • Primary benchmarks: no relevant changes found
  • Secondary benchmarks: 🎉 relevant improvement found
mean1 max count2
Regressions 😿
(primary)
N/A N/A 0
Regressions 😿
(secondary)
N/A N/A 0
Improvements 🎉
(primary)
N/A N/A 0
Improvements 🎉
(secondary)
-0.9% -0.9% 1
All 😿🎉 (primary) N/A N/A 0

Max RSS (memory usage)

Results
  • Primary benchmarks: no relevant changes found
  • Secondary benchmarks: mixed results
mean1 max count2
Regressions 😿
(primary)
N/A N/A 0
Regressions 😿
(secondary)
1.5% 1.8% 2
Improvements 🎉
(primary)
N/A N/A 0
Improvements 🎉
(secondary)
-1.6% -1.6% 1
All 😿🎉 (primary) N/A N/A 0

Cycles

Results
  • Primary benchmarks: 😿 relevant regression found
  • Secondary benchmarks: no relevant changes found
mean1 max count2
Regressions 😿
(primary)
2.7% 2.7% 1
Regressions 😿
(secondary)
N/A N/A 0
Improvements 🎉
(primary)
N/A N/A 0
Improvements 🎉
(secondary)
N/A N/A 0
All 😿🎉 (primary) 2.7% 2.7% 1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

  1. the arithmetic mean of the percent change 2 3

  2. number of relevant changes 2 3

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