[libcu++] Implement tuple-like constructors for `pair` by miscco · Pull Request #9543 · NVIDIA/cccl

miscco · 2026-06-22T13:29:18Z

This implements the pair constructors for tuple-like types and slightly cleans up the constraints type

coderabbitai · 2026-06-22T13:36:27Z

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Walkthrough

Refactors cuda::std::pair constructor SFINAE from __pair_constraints-based members to __select_constructor traits (__tuple_select_default_constructible, __can_construct_implicitly/__can_construct_explicitly) and adds __pair_select_pair_like_constructible_v for pair-like conversions. Updates existing pair and tuple-like tests with const qualifiers, modern trait syntax, and constexpr enforcement. Adds six new conformance tests covering const, move, non-const copy, and pair-like construction paths.

Changes

cuda::std::pair constructor refactor and test suite update

Layer / File(s)	Summary
pair constraint machinery and pair-like selector `libcudacxx/include/cuda/std/__utility/pair.h`, `libcudacxx/include/cuda/std/__fwd/get.h`	Adds tuple-related forward-declaration includes and ADL-get infrastructure macro. Introduces `__pair_select_pair_like_constructible` consteval helper and inline variable template. Removes element-wise boolean members from `__pair_constraints`. Refactors `__pair_base` default constructors (both general and `true`-specialization) to use `__tuple_select_default_constructible` with `__can_construct_implicitly`/`__can_construct_explicitly`.
cuda::std::pair public constructor set rework `libcudacxx/include/cuda/std/__utility/pair.h`	Rewrites all public `cuda::std::pair` constructors—default, element-wise, pair-to-pair converting, and pair-like converting (via `__adl_get`)—to use `__select_constructor` traits and `__pair_select_pair_like_constructible_v` instead of `__pair_constructible`/`__pair_constraints` alias-based SFINAE.
Updates to existing pair and tuple-like tests `libcudacxx/test/libcudacxx/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_tuple_like.pass.cpp`, `const_move_tuple_like.pass.cpp`, `move_tuple_like.pass.cpp`, `non_const_tuple_like.pass.cpp`, `libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_copy.cpp`, `convert_move.cpp`	Adds `const` qualifiers to tuple-like test variables. Adds missing standard library includes (`<complex>`, `<tuple>`) under host-build guards. Updates `is_constructible<...>::value` to `is_constructible_v<...>`. Introduces `constexpr bool test()` functions, expands assertions for `ExplicitT`/`ImplicitT`, and adds `static_assert(test())` enforcement.
New pair-like construction conformance tests `libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_like.pass.cpp`, `const_move_pair_like.pass.cpp`, `move_pair_like.pass.cpp`, `non_const_pair_like.pass.cpp`	Adds tests for implicit/explicit `cuda::std::pair` construction from `array`, `tuple`, and `complex` pair-like sources across const, move, and non-const copy paths, with `TracedCopyMove` dispatch assertions and host-stdlib conditional guards.
New convert_const_move and convert_non_const_copy tests `libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_const_move.cpp`, `convert_non_const_copy.cpp`	Adds `test_pair_rv`/`test_pair_non_const` templates, `DPair` derived wrapper, `ExplicitT`/`ImplicitT` archetypes, and compile-time constructibility/convertibility coverage including `unique_ptr` base/derived transfer, reference-dangling negative cases, and `static_assert(test())` enforcement.

Suggested reviewers

ericniebler
davebayer

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coderabbitai

Actionable comments posted: 4

🧹 Nitpick comments (2)

libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_like.pass.cpp (1)

78-85: 🧹 Nitpick | 🔵 Trivial | ⚡ Quick win

suggestion: use std::complex<double> in this host-only __cpp_lib_tuple_like branch. Line 81 currently uses cuda::std::complex<double>, so this branch re-tests the cuda path instead of the host std tuple-like path.

libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/move_pair_like.pass.cpp (1)

30-87: 🧹 Nitpick | 🔵 Trivial | ⚡ Quick win

suggestion: Consider adding a TEST_FUNC bool test() wrapper and calling test() from main() for consistency with other pair tests (e.g., non_const_pair_like.pass.cpp). If MoveOnly prevents constexpr, document that limitation. Otherwise, add static_assert(test()) to catch issues at compile-time.

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📥 Commits

Reviewing files that changed from the base of the PR and between 5ba76c7 and d7633c3.

📒 Files selected for processing (13)

libcudacxx/include/cuda/std/__utility/pair.h
libcudacxx/test/libcudacxx/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_tuple_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_first_const_second_cxx03.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_move_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_U_V_cxx03.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_const_move.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_copy.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_move.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_non_const_copy.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/move_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/non_const_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/not_constexpr_cxx11.fail.cpp

💤 Files with no reviewable changes (3)

libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/not_constexpr_cxx11.fail.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_first_const_second_cxx03.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_U_V_cxx03.pass.cpp

Jacobfaib · 2026-06-22T13:42:14Z

+    // test_pair_non_const<ConvertingType&&, int>();
+    // test_pair_non_const<ConvertingType const&, int>();
+    // test_pair_non_const<ConvertingType const&&, int>();


Why can't these be tested? We don't care about dangling references in test code no?

I believe the issue is that we should dissallow cnostruction from temporaries, but that requires relatively recent compilers

https://eel.is/c++draft/pairs.pair#13

coderabbitai

Actionable comments posted: 3

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📥 Commits

Reviewing files that changed from the base of the PR and between d7633c3 and a52e267.

📒 Files selected for processing (13)

libcudacxx/include/cuda/std/__utility/pair.h
libcudacxx/test/libcudacxx/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_tuple_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_first_const_second_cxx03.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_move_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_U_V_cxx03.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_const_move.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_copy.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_move.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_non_const_copy.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/move_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/non_const_pair_like.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/not_constexpr_cxx11.fail.cpp

💤 Files with no reviewable changes (3)

libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_first_const_second_cxx03.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/const_pair_U_V_cxx03.pass.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/not_constexpr_cxx11.fail.cpp

✅ Files skipped from review due to trivial changes (1)

libcudacxx/test/libcudacxx/std/utilities/tuple/tuple.tuple/tuple.cnstr/const_tuple_like.pass.cpp

🚧 Files skipped from review as they are similar to previous changes (4)

libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_copy.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_move.cpp
libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_non_const_copy.cpp
libcudacxx/include/cuda/std/__utility/pair.h

coderabbitai

Actionable comments posted: 1

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libcudacxx/include/cuda/std/__fwd/get.h

github-actions · 2026-06-23T20:25:26Z

😬 CI Workflow Results

🟥 Finished in 4h 03m: Pass: 88%/118 | Total: 1d 18h | Max: 1h 03m | Hits: 99%/341045

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miscco requested a review from a team as a code owner June 22, 2026 13:29

miscco requested a review from griwes June 22, 2026 13:29

github-project-automation Bot added this to CCCL Jun 22, 2026

github-project-automation Bot moved this to Todo in CCCL Jun 22, 2026

cccl-authenticator-app Bot moved this from Todo to In Review in CCCL Jun 22, 2026

miscco force-pushed the tuple_like_pair branch from d7633c3 to a52e267 Compare June 22, 2026 13:32

coderabbitai Bot reviewed Jun 22, 2026

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Jacobfaib reviewed Jun 22, 2026

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miscco force-pushed the tuple_like_pair branch from 7ff1f03 to 838c678 Compare June 22, 2026 14:04

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Comment thread libcudacxx/include/cuda/std/__fwd/get.h Outdated

miscco force-pushed the tuple_like_pair branch from 4876b4a to ae513cf Compare June 22, 2026 17:02

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miscco enabled auto-merge (squash) June 23, 2026 07:06

miscco added 7 commits June 23, 2026 10:48

[libcu++] Reuse tuple machinery for pair default constructor

81cffc5

[libcu++] Reuse tuple constraints for pair elementwise constructor

52e617d

[libcu++] Refactor pair-like constructors

c07a9ee

Address review comments

f7fd64c

Add _CCCL_EXECK_CHECK_DISABLE to __adl_get

1e42ac6

Suppress warning

1177d4e

Disambiguate pair-like constructor form pair

41d6eef

miscco force-pushed the tuple_like_pair branch from ae513cf to 41d6eef Compare June 23, 2026 08:51

davebayer reviewed Jun 23, 2026

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Expand testing

bc1ae80

davebayer reviewed Jun 23, 2026

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Comment thread libcudacxx/test/libcudacxx/std/utilities/utility/pairs/pairs.pair/convert_const_move.cpp Outdated

Jacobfaib approved these changes Jun 23, 2026

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Greatly expand testing

9901376

miscco force-pushed the tuple_like_pair branch from f41cc03 to 9901376 Compare June 23, 2026 16:19

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miscco commented Jun 22, 2026

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github-actions Bot commented Jun 23, 2026

😬 CI Workflow Results

🟥 Finished in 4h 03m: Pass: 88%/118 | Total: 1d 18h | Max: 1h 03m | Hits: 99%/341045

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coderabbitai Bot commented Jun 22, 2026 •

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