<random>: Avoid copying vectors in distribution comparisons - #6454
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A. Jiang (frederick-vs-ja) wants to merge 1 commit into
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A. Jiang (frederick-vs-ja) wants to merge 1 commit into
A. Jiang (frederick-vs-ja) wants to merge 1 commit into
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It is just unreasonable to perform dynamic allocation in such comparisons. Ideally, these `operator==`s (and corresponding `operator!=` until C++20) should also be `noexcept`, but we haven't strengthened exception specification for `vector`'s `operator==` yet.
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A. Jiang (frederick-vs-ja)
September 17, 2026 07:27
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🟢 Approval recommended
The direct comparisons preserve behavior while eliminating unnecessary allocations.
Pull request overview
Optimizes random distribution equality comparisons by avoiding temporary param_type objects and their vector allocations.
Changes:
- Compares stored parameter objects directly for three vector-backed distributions.
- Preserves existing equality semantics.
File summaries
| File | Description |
|---|---|
stl/inc/random |
Avoids parameter-vector copies in distribution comparisons. |
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Stephan T. Lavavej (StephanTLavavej)
requested changes
Sep 18, 2026
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| _NODISCARD friend bool operator==(const discrete_distribution& _Left, const discrete_distribution& _Right) { | ||
| return _Left.param() == _Right.param(); | ||
| return _Left._Par == _Right._Par; |
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These might be the only ones where it matters in release mode, but IMO I think we should now be implementing all of the distribution operator== by directly inspecting _Par instead of calling param(). It's more consistent throughout the file, and happens to improve debugging and debug codegen.
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It is just unreasonable to perform dynamic allocation in such comparisons.
Ideally, these
operator==s (and correspondingoperator!=until C++20) should also benoexcept, but we haven't strengthened exception specification forvector'soperator==yet.