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iter: specialize Take::count using advance_by - #160139

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Rachit2323:take-count-specialization
Jul 30, 2026
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iter: specialize Take::count using advance_by#160139
rust-bors[bot] merged 1 commit into
rust-lang:mainfrom
Rachit2323:take-count-specialization

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@Rachit2323

@Rachit2323 Rachit2323 commented Jul 29, 2026

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Right now, when you call .count() on a Take iterator, it visits every single item one by one just to count them. That's slow.

For example, if you have 1000 items and call .take(5).count(), it should just skip 5 items and return 5 — but today it actually goes through each item manually.

This PR fixes that by using advance_by to skip items in bulk instead of visiting each one. After the skip, we know exactly how many items were consumed, so we return that number directly.

This makes .count() faster for Take iterators, especially when the underlying iterator supports fast skipping.

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. 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 Jul 29, 2026
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r? @jhpratt

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@joboet

joboet commented Jul 29, 2026

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The change to count is fine, but this PR contains other unrelated fixes. Please remove those.

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@rustbot rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 29, 2026
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Reminder, once the PR becomes ready for a review, use @rustbot ready.

@rustbot rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jul 29, 2026
@Rachit2323
Rachit2323 force-pushed the take-count-specialization branch from 28c8b02 to d800217 Compare July 29, 2026 15:35
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joboet commented Jul 29, 2026

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Thanks!
@bors r+ rollup
r? joboet

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📌 Commit d800217 has been approved by joboet

It is now in the queue for this repository.

@rust-bors rust-bors Bot added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Jul 29, 2026
@rust-bors rust-bors Bot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jul 29, 2026
jhpratt added a commit to jhpratt/rust that referenced this pull request Jul 29, 2026
@jhpratt
Rollup merge of rust-lang#160139 - Rachit2323:take-count-specializati…
47f5240 
…on, r=joboet

iter: specialize Take::count using advance_by

Right now, when you call .count() on a Take iterator, it visits every single item one by one just to count them. That's slow.

For example, if you have 1000 items and call .take(5).count(), it should just skip 5 items and return 5 — but today it actually goes through each item manually.

This PR fixes that by using advance_by to skip items in bulk instead of visiting each one. After the skip, we know exactly how many items were consumed, so we return that number directly.

This makes .count() faster for Take iterators, especially when the underlying iterator supports fast skipping.
@jhpratt jhpratt mentioned this pull request Jul 29, 2026
Closed
rust-bors Bot pushed a commit that referenced this pull request Jul 29, 2026
@bors
Auto merge of #160174 - jhpratt:rollup-2pBeTwD, r=jhpratt
a981d4b 
Rollup of 18 pull requests

Successful merges:

 - #159130 (a bit optimize four-digit chunks in integer formatting)
 - #159592 (core: implement bounded random sampling)
 - #159898 (Add intrinsic-test alias and set  sample rate)
 - #158247 (hermit/fs: Return `unsupported()` instead of `from_raw_os_error(22)`)
 - #158649 (Hermit: fix `readdir()` )
 - #159049 (Avoid ICE in From/TryFrom cast suggestion when encountering HRTBs)
 - #160053 (test: add test suite for the 85681 issue)
 - #160087 (Add regression test for nested associated-type projection ICE)
 - #160090 (rustc_resolve: Further reduce mutability in resolver)
 - #160099 (Resolver: split module resolutions into local and external resolutions)
 - #160106 (Add suggestions for `must_implement_one_of`)
 - #160117 (Remove unnecessary format usage)
 - #160134 (Work around Wine bug 60084 by calling WSAStartup at most once)
 - #160139 (iter: specialize Take::count using advance_by)
 - #160142 (bootstrap: remove use-lld config alias)
 - #160148 (Rename `errors.rs` file to `diagnostics.rs` (15/N))
 - #160151 (Mark a doctest as requiring unwinding)
 - #160166 (Use correct feature gates for `f16`/`f128` `From` impls)
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request Jul 29, 2026
@JonathanBrouwer
Rollup merge of rust-lang#160139 - Rachit2323:take-count-specializati…
2b2567a 
…on, r=joboet

iter: specialize Take::count using advance_by

Right now, when you call .count() on a Take iterator, it visits every single item one by one just to count them. That's slow.

For example, if you have 1000 items and call .take(5).count(), it should just skip 5 items and return 5 — but today it actually goes through each item manually.

This PR fixes that by using advance_by to skip items in bulk instead of visiting each one. After the skip, we know exactly how many items were consumed, so we return that number directly.

This makes .count() faster for Take iterators, especially when the underlying iterator supports fast skipping.
@JonathanBrouwer JonathanBrouwer mentioned this pull request Jul 29, 2026
Closed
rust-bors Bot pushed a commit that referenced this pull request Jul 29, 2026
@bors
Auto merge of #160182 - JonathanBrouwer:rollup-5J0H0ej, r=JonathanBro…
aac6f26 
…uwer

Rollup of 18 pull requests

Successful merges:

 - #159898 (Add intrinsic-test alias and set  sample rate)
 - #158247 (hermit/fs: Return `unsupported()` instead of `from_raw_os_error(22)`)
 - #158649 (Hermit: fix `readdir()` )
 - #158693 (Add type-check to offload intrinisc calls)
 - #159049 (Avoid ICE in From/TryFrom cast suggestion when encountering HRTBs)
 - #159411 ([rustdoc] Correctly handle output options with --show-coverage)
 - #160053 (test: add test suite for the 85681 issue)
 - #160087 (Add regression test for nested associated-type projection ICE)
 - #160090 (rustc_resolve: Further reduce mutability in resolver)
 - #160099 (Resolver: split module resolutions into local and external resolutions)
 - #160106 (Add suggestions for `must_implement_one_of`)
 - #160117 (Remove unnecessary format usage)
 - #160134 (Work around Wine bug 60084 by calling WSAStartup at most once)
 - #160139 (iter: specialize Take::count using advance_by)
 - #160142 (bootstrap: remove use-lld config alias)
 - #160148 (Rename `errors.rs` file to `diagnostics.rs` (15/N))
 - #160151 (Mark a doctest as requiring unwinding)
 - #160166 (Use correct feature gates for `f16`/`f128` `From` impls)
@jhpratt jhpratt mentioned this pull request Jul 30, 2026
Merged
rust-bors Bot pushed a commit that referenced this pull request Jul 30, 2026
@bors
Auto merge of #160190 - jhpratt:rollup-5Fioy6q, r=jhpratt
d108471 
Rollup of 20 pull requests

Successful merges:

 - #157669 (cfi: add diag mode support)
 - #158247 (hermit/fs: Return `unsupported()` instead of `from_raw_os_error(22)`)
 - #158649 (Hermit: fix `readdir()` )
 - #158693 (Add type-check to offload intrinisc calls)
 - #159049 (Avoid ICE in From/TryFrom cast suggestion when encountering HRTBs)
 - #159411 ([rustdoc] Correctly handle output options with --show-coverage)
 - #160053 (test: add test suite for the 85681 issue)
 - #160087 (Add regression test for nested associated-type projection ICE)
 - #160090 (rustc_resolve: Further reduce mutability in resolver)
 - #160099 (Resolver: split module resolutions into local and external resolutions)
 - #160101 (Add missing `needs-unwind` annotation to `add-spawn-hook-reentrancy-159923` test)
 - #160106 (Add suggestions for `must_implement_one_of`)
 - #160117 (Remove unnecessary format usage)
 - #160134 (Work around Wine bug 60084 by calling WSAStartup at most once)
 - #160139 (iter: specialize Take::count using advance_by)
 - #160142 (bootstrap: remove use-lld config alias)
 - #160148 (Rename `errors.rs` file to `diagnostics.rs` (15/N))
 - #160151 (Mark a doctest as requiring unwinding)
 - #160166 (Use correct feature gates for `f16`/`f128` `From` impls)
 - #160178 (Remove unused `va_start` intrinsic)
rust-bors Bot pushed a commit that referenced this pull request Jul 30, 2026
@bors
Auto merge of #160190 - jhpratt:rollup-5Fioy6q, r=jhpratt
be3d26d 
Rollup of 20 pull requests

Successful merges:

 - #157669 (cfi: add diag mode support)
 - #158247 (hermit/fs: Return `unsupported()` instead of `from_raw_os_error(22)`)
 - #158649 (Hermit: fix `readdir()` )
 - #158693 (Add type-check to offload intrinisc calls)
 - #159049 (Avoid ICE in From/TryFrom cast suggestion when encountering HRTBs)
 - #159411 ([rustdoc] Correctly handle output options with --show-coverage)
 - #160053 (test: add test suite for the 85681 issue)
 - #160087 (Add regression test for nested associated-type projection ICE)
 - #160090 (rustc_resolve: Further reduce mutability in resolver)
 - #160099 (Resolver: split module resolutions into local and external resolutions)
 - #160101 (Add missing `needs-unwind` annotation to `add-spawn-hook-reentrancy-159923` test)
 - #160106 (Add suggestions for `must_implement_one_of`)
 - #160117 (Remove unnecessary format usage)
 - #160134 (Work around Wine bug 60084 by calling WSAStartup at most once)
 - #160139 (iter: specialize Take::count using advance_by)
 - #160142 (bootstrap: remove use-lld config alias)
 - #160148 (Rename `errors.rs` file to `diagnostics.rs` (15/N))
 - #160151 (Mark a doctest as requiring unwinding)
 - #160166 (Use correct feature gates for `f16`/`f128` `From` impls)
 - #160178 (Remove unused `va_start` intrinsic)
@rust-bors
rust-bors Bot merged commit d1e43eb into rust-lang:main Jul 30, 2026
13 checks passed
@rustbot rustbot added this to the 1.99.0 milestone Jul 30, 2026
rust-timer added a commit that referenced this pull request Jul 30, 2026
@rust-timer
Unrolled build for #160139
da323d0 
Rollup merge of #160139 - Rachit2323:take-count-specialization, r=joboet

iter: specialize Take::count using advance_by

Right now, when you call .count() on a Take iterator, it visits every single item one by one just to count them. That's slow.

For example, if you have 1000 items and call .take(5).count(), it should just skip 5 items and return 5 — but today it actually goes through each item manually.

This PR fixes that by using advance_by to skip items in bulk instead of visiting each one. After the skip, we know exactly how many items were consumed, so we return that number directly.

This makes .count() faster for Take iterators, especially when the underlying iterator supports fast skipping.
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