Add __lazy_call_or

[Jacobfaib]

Description

Add cuda::__lazy_call_or, which acts like cuda::__call_or except that the default value is lazily computed.

Checklist

• New or existing tests cover these changes.
• The documentation is up to date with these changes.

Summary by CodeRabbit

• New Features

  • Added conditional callable invocation utility with lazy fallback evaluation support, enabling deferred callable selection based on runtime conditions.

• Tests

  • Added comprehensive test suite validating the new utility's behavior, including noexcept correctness, constexpr compatibility, and lazy evaluation semantics.

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[Jacobfaib]

/ok to test

[Jacobfaib]

/ok to test

[Jacobfaib]

/ok to test

[github-actions]

🥳 CI Workflow Results

🟩 Finished in 3h 36m: Pass: 100%/110 | Total: 3d 18h | Max: 3h 36m | Hits: 72%/317059

See results here.

[jrhemstad]

@coderabbitai full review

[coderabbitai]

✅ Actions performed

Full review triggered.

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Enterprise

Run ID: e9de7de1-ac13-4c98-9f40-dbc0e404bdc1

📥 Commits

Reviewing files that changed from the base of the PR and between c251a2d and 41c0a78.

📒 Files selected for processing (2)

• libcudacxx/include/cuda/__functional/lazy_call_or.h
• libcudacxx/test/libcudacxx/cuda/functional/lazy_call_or.pass.cpp

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Walkthrough

Adds a new CUDA C++ customization point object __lazy_call_or that conditionally invokes a primary callable with forwarded arguments, or falls back to invoking a zero-argument fallback callable. Includes a companion result type alias __lazy_call_result_or_t and comprehensive test coverage validating result types, noexcept propagation, constexpr evaluation, lazy fallback evaluation, and value category forwarding.

Changes

Lazy Conditional Call CPO

Layer / File(s)	Summary
Core CPO Implementation libcudacxx/include/cuda/__functional/lazy_call_or.h	Defines __lazy_call_or CPO with two operator() overloads: one forwards args... to the primary callable, another ignores the primary and invokes fallback_callable() with zero arguments. Includes __lazy_call_result_or_t alias for return type deduction.
Comprehensive Test Suite libcudacxx/test/libcudacxx/cuda/functional/lazy_call_or.pass.cpp	Tests result type correctness, noexcept propagation for callable and fallback paths, constexpr evaluation, lazy evaluation (fallback not invoked unless selected), and value category forwarding for lvalue/rvalue arguments.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A lazy call hops both ways—
Primary path or fallback plays,
Zero-arg hops deferred with care,
Forwarded args float through the air,
Whiskers twitch at noexcept praise!

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Add __lazy_call_or' accurately describes the main change—introducing a new CUDA C++ CPO for lazy fallback evaluation. It is concise, specific, and directly related to the primary contribution.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

Review ran into problems

🔥 Problems

Timed out fetching pipeline failures after 30000ms

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