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[libc++][NFC] Add a static assertion to document an assumption in std::hash #114440

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Merged
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Nov 1, 2024
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[libc++][NFC] Add a static assertion to document an assumption in std::hash #114440

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6 changes: 5 additions & 1 deletion libcxx/include/__functional/hash.h
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Original file line number Diff line number Diff line change
Expand Up @@ -406,7 +406,11 @@ struct _LIBCPP_TEMPLATE_VIS hash<long> : public __unary_function<long, size_t> {

template <>
struct _LIBCPP_TEMPLATE_VIS hash<unsigned long> : public __unary_function<unsigned long, size_t> {
_LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
_LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned long __v) const _NOEXCEPT {
static_assert(sizeof(size_t) >= sizeof(unsigned long),
"This would be a terrible hash function on a platform where size_t is smaller than unsigned long");
return static_cast<size_t>(__v);
}
};

template <>
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