Implement DoubleEnded and ExactSize for Take<Repeat> and Take<RepeatWith> #106943

mina86 · 2023-01-16T17:40:19Z

Repeat iterator always returns the same element and behaves the same way
backwards and forwards. Take iterator can trivially implement backwards
iteration over Repeat inner iterator by simply doing forwards iteration.

DoubleEndedIterator is not currently implemented for Take<Repeat>
because Repeat doesn’t implement ExactSizeIterator which is a required
bound on DEI implementation for Take.

Similarly, since Repeat is an infinite iterator which never stops, Take
can trivially know how many elements it’s going to return. This allows
implementing ExactSizeIterator on Take<Repeat>.

While at it, observe that ExactSizeIterator can also be implemented for
Take<RepeatWhile> so add that implementation too. Since in contrast
to Repeat, RepeatWhile doesn’t guarante to always return the same value,
DoubleEndedIterator isn’t implemented.

Those changes render core::iter::repeat_n somewhat redundant.

Issue: #104434
Issue: #104729

ACP: ACP: Uplift iter::repeat_n from itertools libs-team#120 (this is actually ACP for repeat_n but this is nearly the same functionality so hijacking it so both approaches can be discussed in one place)

…ith> Repeat iterator always returns the same element and behaves the same way backwards and forwards. Take iterator can trivially implement backwards iteration over Repeat inner iterator by simply doing forwards iteration. DoubleEndedIterator is not currently implemented for Take<Repeat<T>> because Repeat doesn’t implement ExactSizeIterator which is a required bound on DEI implementation for Take. Similarly, since Repeat is an infinite iterator which never stops, Take can trivially know how many elements it’s going to return. This allows implementing ExactSizeIterator on Take<Repeat<T>>. While at it, observe that ExactSizeIterator can also be implemented for Take<RepeatWhile<F>> so add that implementation too. Since in contrast to Repeat, RepeatWhile doesn’t guarante to always return the same value, DoubleEndedIterator isn’t implemented. Those changes render core::iter::repeat_n somewhat redundant. Issue: rust-lang#104434 Issue: rust-lang#104729

rustbot · 2023-01-16T17:40:26Z

r? @cuviper

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rustbot · 2023-01-16T17:40:29Z

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 @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. 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.

Examples of T-libs-api changes:

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Changing observable runtime behavior of library APIs

mina86 · 2023-01-16T17:40:44Z

@rustbot label +T-libs-api -T-libs

cuviper · 2023-01-16T18:18:20Z

r? libs-api

dtolnay · 2023-01-22T19:56:15Z

Reassigning BurntSushi's reviews because based on git log -i --grep=r=burntsushi the last time they did rust-lang/rust reviews was over 3 years ago.

r? rust-lang/libs-api

pitaj · 2023-01-28T19:42:15Z

I believe this requires an ACP, since it introduces an insta-stable change by adding a new implementation of an existing stable trait on an existing stable type.

Please open one (if you haven't already). Then link it here and mark the PR as S-waiting-on-ACP.

@rustbot label -S-waiting-on-review +S-waiting-on-author

mina86 · 2023-01-28T21:06:47Z

Sorry, I missed the requirement for ACP. So actually, rather than creating a new one, I’ve just pinged ACP for repeat_n. This approach was actually suggested there already. The ACP is: rust-lang/libs-team#120

mina86 · 2023-01-28T21:09:02Z

@rustbot label -S-waiting-on-author +S-waiting-on-ACP

workingjubilee · 2023-07-31T22:41:03Z

... is it really an ExactSizeIterator if it's infinite?

pitaj · 2023-07-31T22:47:57Z

... is it really an ExactSizeIterator if it's infinite?

This only adds that impl for Take<Repeat>, which has a known finite size.

workingjubilee · 2023-07-31T22:51:59Z

...
......
........
right.

I'll uh...
r? libs-api Needs FCP for this set of trait impls that offer effectively an alternative to the repeat_n function.

bors · 2024-08-16T22:46:53Z

⌛ Testing commit ebf79b5 with merge 9dda6ac...

…lnay Implement DoubleEnded and ExactSize for Take<Repeat> and Take<RepeatWith> Repeat iterator always returns the same element and behaves the same way backwards and forwards. Take iterator can trivially implement backwards iteration over Repeat inner iterator by simply doing forwards iteration. DoubleEndedIterator is not currently implemented for Take<Repeat<T>> because Repeat doesn’t implement ExactSizeIterator which is a required bound on DEI implementation for Take. Similarly, since Repeat is an infinite iterator which never stops, Take can trivially know how many elements it’s going to return. This allows implementing ExactSizeIterator on Take<Repeat<T>>. While at it, observe that ExactSizeIterator can also be implemented for Take<RepeatWhile<F>> so add that implementation too. Since in contrast to Repeat, RepeatWhile doesn’t guarante to always return the same value, DoubleEndedIterator isn’t implemented. Those changes render core::iter::repeat_n somewhat redundant. Issue: rust-lang#104434 Issue: rust-lang#104729 - [ ] ACP: rust-lang/libs-team#120 (this is actually ACP for repeat_n but this is nearly the same functionality so hijacking it so both approaches can be discussed in one place)

bors · 2024-08-16T22:50:48Z

💔 Test failed - checks-actions

dtolnay · 2024-08-16T23:52:47Z

Needs a rebase to fix the conflict with #120486.

dtolnay · 2024-08-16T23:59:05Z

- fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
+ fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {

@bors r+

bors · 2024-08-16T23:59:07Z

📌 Commit 994e712 has been approved by dtolnay

It is now in the queue for this repository.

bors · 2024-08-17T01:46:28Z

⌛ Testing commit 994e712 with merge f24a6ba...

bors · 2024-08-17T04:10:23Z

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing f24a6ba to master...

rust-timer · 2024-08-17T05:50:40Z

Finished benchmarking commit (f24a6ba): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

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	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-3.1%, -3.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.1%	[-3.1%, -3.1%]	1

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Bootstrap: 750.979s -> 749.822s (-0.15%)
Artifact size: 339.14 MiB -> 339.18 MiB (0.01%)

After rust/rust-lang#106943 the part about `ExactSizeIterator` is no longer valid

…s-not-that-special-anymore, r=jhpratt Remove outdated documentation for `repeat_n` After rust-lang#106943, which made `Take<Repeat>` implement `ExactSizeIterator`, part of documentation about difference from `repeat(x).take(n)` is no longer valid. `@rustbot` labels: +A-docs, +A-iterators

…s-not-that-special-anymore, r=jhpratt Remove outdated documentation for `repeat_n` After rust-lang#106943, which made `Take<Repeat>` implement `ExactSizeIterator`, part of documentation about difference from `repeat(x).take(n)` is no longer valid. ``@rustbot`` labels: +A-docs, +A-iterators

…s-not-that-special-anymore, r=jhpratt Remove outdated documentation for `repeat_n` After rust-lang#106943, which made `Take<Repeat>` implement `ExactSizeIterator`, part of documentation about difference from `repeat(x).take(n)` is no longer valid. ```@rustbot``` labels: +A-docs, +A-iterators

…s-not-that-special-anymore, r=jhpratt Remove outdated documentation for `repeat_n` After rust-lang#106943, which made `Take<Repeat>` implement `ExactSizeIterator`, part of documentation about difference from `repeat(x).take(n)` is no longer valid. ````@rustbot```` labels: +A-docs, +A-iterators

Rollup merge of rust-lang#131858 - AnthonyMikh:AnthonyMikh/repeat_n-is-not-that-special-anymore, r=jhpratt Remove outdated documentation for `repeat_n` After rust-lang#106943, which made `Take<Repeat>` implement `ExactSizeIterator`, part of documentation about difference from `repeat(x).take(n)` is no longer valid. ````@rustbot```` labels: +A-docs, +A-iterators

rustbot assigned cuviper Jan 16, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Jan 16, 2023

rustbot 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 Jan 16, 2023

mina86 changed the title ~~Implement DoubleEndedIterator and ExactSizeIterator for Take<Repaet<T>>~~ Implement DoubleEndedIterator and ExactSizeIterator for Take<Repeat<T>> Jan 16, 2023

mina86 force-pushed the exact_size_take_repeat branch from 45de24d to 5d1590d Compare January 16, 2023 17:42

rustbot assigned BurntSushi and unassigned cuviper Jan 16, 2023

rustbot assigned joshtriplett and unassigned BurntSushi Jan 22, 2023

rustbot 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 Jan 28, 2023

mina86 mentioned this pull request Jan 28, 2023

ACP: Uplift iter::repeat_n from itertools rust-lang/libs-team#120

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rustbot added S-waiting-on-ACP Status: PR has an ACP and is waiting for the ACP to complete. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jan 28, 2023

workingjubilee added the needs-fcp This change is insta-stable, so needs a completed FCP to proceed. label Jul 31, 2023

rustbot assigned m-ou-se Jul 31, 2023

bors added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Aug 16, 2024

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bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Aug 16, 2024

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dtolnay force-pushed the exact_size_take_repeat branch from ebf79b5 to 994e712 Compare August 16, 2024 23:58

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-review Status: Awaiting review from the assignee but also interested parties. labels Aug 16, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Aug 17, 2024

bors merged commit f24a6ba into rust-lang:master Aug 17, 2024
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rustbot added this to the 1.82.0 milestone Aug 17, 2024

mina86 deleted the exact_size_take_repeat branch August 19, 2024 07:33

apiraino removed the to-announce Announce this issue on triage meeting label Aug 22, 2024

AnthonyMikh added a commit to AnthonyMikh/rust that referenced this pull request Oct 17, 2024

remove outdated documentation for repeat_n

cdacdae

After rust/rust-lang#106943 the part about `ExactSizeIterator` is no longer valid

AnthonyMikh mentioned this pull request Oct 17, 2024

Remove outdated documentation for repeat_n #131858

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Implement DoubleEnded and ExactSize for Take<Repeat> and Take<RepeatWith> #106943

Implement DoubleEnded and ExactSize for Take<Repeat> and Take<RepeatWith> #106943

mina86 commented Jan 16, 2023 •

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Implement DoubleEnded and ExactSize for Take<Repeat> and Take<RepeatWith> #106943

Implement DoubleEnded and ExactSize for Take<Repeat> and Take<RepeatWith> #106943

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Overall result: no relevant changes - no action needed

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mina86 commented Jan 16, 2023 •

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