[libc++] Implement `views::join_with` #65536

JMazurkiewicz · 2023-09-06T21:40:41Z

Implement "P2441R2 views::join_with" (https://wg21.link/P2441R2), closes P2441R2: views::join_with #105185
Implement LWG4074 (https://wg21.link/LWG4074), closes LWG4074: compatible-joinable-ranges is underconstrained #105346
Complete implementation of "P2711R1 Making multi-param constructors of views explicit" (https://wg21.link/P2711R1), closes P2711R1: Making multi-param constructors of views explicit #105252
Complete implementation of "P2770R0 Stashing stashing iterators for proper flattening" (https://wg21.link/P2770R0), closes P2770R0: Stashing stashing iterators for proper flattening #105250

libcxx/docs/Status/Cxx23Papers.csv

ldionne · 2023-09-15T20:55:42Z

@JMazurkiewicz Please ping us when this is ready to review and make it a non-draft.

This patch adds a mention that the following papers are in progress: * P2770R0: #66033 * P2441R2 and P2711R1: #65536

github-actions · 2024-02-03T00:00:05Z

✅ With the latest revision this PR passed the C/C++ code formatter.

H-G-Hristov · 2024-05-10T14:27:22Z

I guess with constexpr variant this cool feature can be finalized now :)

…s.cpp`) Comment: llvm#65536 (comment)

Comment: llvm#65536 (comment)

…s.cpp`) Comment: llvm#65536 (comment)

Comment: llvm#65536 (comment) Drive-by: make use of new aliases

Comment: llvm#65536 (comment)

…with

Zingam · 2025-01-18T08:58:27Z

@JMazurkiewicz At the top you mention that this PR completed several papers. Do you need to add additional GitHub issues to the list that this PR closes/fixes/?

…with

Instead of `// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20`

…with

https://www.githubstatus.com/incidents/nm83zrdky73y

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JMazurkiewicz · 2025-04-14T15:25:19Z

Ping @huixie90

…with

huixie90

LGTM with some nits. Thanks very much for the patch!

huixie90 · 2025-05-09T11:55:54Z

libcxx/docs/ReleaseNotes/21.rst

@@ -47,6 +47,9 @@ Implemented Papers
 - P1222R4: A Standard ``flat_set`` (`Github <https://github.com/llvm/llvm-project/issues/105193>`__)
 - P2897R7: ``aligned_accessor``: An mdspan accessor expressing pointer over-alignment (`Github <https://github.com/llvm/llvm-project/issues/118372>`__)
 - P3247R2: Deprecate the notion of trivial types (`Github <https://github.com/llvm/llvm-project/issues/118387>`__)
+- P2441R2: ``views::join_with`` (`Github <https://github.com/llvm/llvm-project/issues/105185>`__)
+- P2711R1: Making multi-param constructors of ``views`` ``explicit`` (`Github <https://github.com/llvm/llvm-project/issues/105252>`__)


question: is this paper completely done? I saw P2441R2 has multiple changes in different views

I think the rest of P2711 is already done in libc++ 17.

I confirm. I think it was my first contribution.

huixie90 · 2025-05-09T12:06:15Z

libcxx/include/__ranges/join_with_view.h

+
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() {


is there a reason why [[__nodiscard__]] is used rather than [[nodiscard]]?

also I notice that we don't add [[nodiscard]] in ranges library yet. not that I am against nodiscard, but I am not sure what we generally do in this case. For example, begin can be mutating and there might be a legitimate use case where begin is called explicitly to cache the results and discard it.

@ldionne I wonder what is the policy in Libc++ for adding no_discard

This should use the non-ugly spelling. Re. policy, we have https://libcxx.llvm.org/CodingGuidelines.html#apply-nodiscard-where-relevant. In this case I think it's fine. This would most likely fall under "only observe a value" or "is most likely a misuse of the function". While it's technically possible that someone might call begin() to cache something, this would definitely require a comment in code, and having to add a void cast seems fine to me in that case.

huixie90 · 2025-05-09T12:25:02Z

libcxx/include/__ranges/join_with_view.h

+struct __join_with_view_iterator_category {};
+
+template <class _Base, class _PatternBase, class _InnerBase>
+  requires is_reference_v<range_reference_t<_Base>> && forward_range<_Base> && forward_range<_InnerBase>


is_reference_v<range_reference_t<_Base>> is still correct but the spec is using is_reference_v<InnerBase> , which is simpler

huixie90 · 2025-05-09T13:54:55Z

libcxx/include/__ranges/join_with_view.h

+  template <bool _OtherConst>
+    requires sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI constexpr bool __equal_to(const __iterator<_OtherConst>& __x) const {
+    return __x.__get_outer() == __end_;


what is the reason to have this member function? is it just for the private access? if so, i would recommend to just have a static member function to access the private member of iterator. it is quite verbose here with the complex requires expression

ldionne · 2025-05-12T20:52:48Z

Sorry for the churn about the pending-ci tag -- I missed that there were still a few comments to resolve before merging.

github-actions bot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Sep 6, 2023

JMazurkiewicz force-pushed the libcxx/ranges/join_with branch 5 times, most recently from 3259db4 to 0481670 Compare September 8, 2023 00:07

Zingam reviewed Sep 8, 2023

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JMazurkiewicz force-pushed the libcxx/ranges/join_with branch from 0481670 to f113229 Compare September 8, 2023 15:11

ldionne assigned var-const and huixie90 and unassigned var-const Sep 13, 2023

ldionne requested a review from huixie90 September 15, 2023 20:55

philnik777 added the ranges Issues related to `<ranges>` label Oct 6, 2023

JMazurkiewicz mentioned this pull request Oct 24, 2023

[libc++] Update status of P2770R0, P2441R2 and P2711R1 papers #70045

Merged

ldionne pushed a commit that referenced this pull request Oct 24, 2023

[libc++] Update status of P2770R0, P2441R2 and P2711R1 (#70045)

e1e0598

This patch adds a mention that the following papers are in progress: * P2770R0: #66033 * P2441R2 and P2711R1: #65536

JMazurkiewicz force-pushed the libcxx/ranges/join_with branch from f113229 to 1835f68 Compare February 2, 2024 23:57

JMazurkiewicz marked this pull request as ready for review February 4, 2024 14:58

JMazurkiewicz requested a review from a team as a code owner February 4, 2024 14:58

JMazurkiewicz force-pushed the libcxx/ranges/join_with branch 3 times, most recently from a84985a to fcdf64a Compare May 14, 2024 14:38

JMazurkiewicz force-pushed the libcxx/ranges/join_with branch 3 times, most recently from 54a741c to a9a1031 Compare May 22, 2024 23:17

JMazurkiewicz force-pushed the libcxx/ranges/join_with branch from a9a1031 to 9406093 Compare June 5, 2024 09:49

JMazurkiewicz added 9 commits January 9, 2025 22:40

Make sure CIter and Iter are different types (`ctor.not_const.pas…

14471bc

…s.cpp`) Comment: llvm#65536 (comment)

Make sure CIter and Iter are different types (eq.pass.cpp)

52ad025

Comment: llvm#65536 (comment)

Make sure CSent and Sent are different types (`ctor.not_const.pas…

d52bdbf

…s.cpp`) Comment: llvm#65536 (comment)

Make sure CSent and Sent are different types (eq.pass.cpp)

96eae0b

Comment: llvm#65536 (comment) Drive-by: make use of new aliases

Add missing <array> include in iter_swap.pass.cpp

0dc76bb

Fix sentinel::operator==

9760ec3

Comment: llvm#65536 (comment)

Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

8ebaa0c

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Fix formatting

d9d0033

Clarify some comments in test_post_increment

d3c014f

JMazurkiewicz added 14 commits January 28, 2025 22:12

Use _LIBCPP_NODEBUG attribute

abe8ab9

Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

4972ccc

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[NFC] Use // REQUIRES: std-at-least-c++23

4601812

Instead of `// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20`

More _LIBCPP_NODEBUG

9847c22

Fix unstable ABI tests

6a4a0a4

Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

dfe5543

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Target LLVM 21

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Trigger CI due to GitHub "incident"

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https://www.githubstatus.com/incidents/nm83zrdky73y

Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

966b3bb

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Add links to GitHub in 21.rst

3d54775

Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

10fdb29

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Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

30d02a1

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Don't use std::is_trivial (deprecated in C++26)

6950e48

Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

41b935b

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Merge remote-tracking branch 'upstream/main' into libcxx/ranges/join_…

a0420dc

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huixie90 approved these changes May 9, 2025

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ldionne added pending-ci Merging the PR is only pending completion of CI and removed pending-ci Merging the PR is only pending completion of CI labels May 12, 2025

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[libc++] Implement `views::join_with` #65536

[libc++] Implement `views::join_with` #65536

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ldionne commented May 12, 2025


		[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }

		[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() {

[libc++] Implement views::join_with #65536

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[libc++] Implement views::join_with #65536

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ldionne commented May 12, 2025

[libc++] Implement `views::join_with` #65536

[libc++] Implement `views::join_with` #65536

JMazurkiewicz commented Sep 6, 2023 •

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