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Use if constexpr dispatch for _Pass_fn #3389

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merged 2 commits into from
Feb 11, 2023
Merged

Use if constexpr dispatch for _Pass_fn #3389

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76347a1
Use `if constexpr` dispatch for `_Pass_fn`
CaseyCarter Feb 5, 2023
28b5698
miscco's review comments
CaseyCarter Feb 6, 2023
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20 changes: 8 additions & 12 deletions stl/inc/xutility
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Original file line number Diff line number Diff line change
Expand Up @@ -360,7 +360,6 @@ _EXPORT_STD struct identity {
};
#endif // _HAS_CXX20

// TRANSITION, VSO-386225
template <class _Fx>
struct _Ref_fn { // pass function object by value as a reference
template <class... _Args>
Expand All @@ -376,17 +375,14 @@ struct _Ref_fn { // pass function object by value as a reference
};

template <class _Fn>
_INLINE_VAR constexpr bool _Pass_functor_by_value_v = conjunction_v<bool_constant<sizeof(_Fn) <= sizeof(void*)>,
is_trivially_copy_constructible<_Fn>, is_trivially_destructible<_Fn>>;

template <class _Fn, enable_if_t<_Pass_functor_by_value_v<_Fn>, int> = 0> // TRANSITION, if constexpr
constexpr _Fn _Pass_fn(_Fn _Val) { // pass functor by value
return _Val;
}

template <class _Fn, enable_if_t<!_Pass_functor_by_value_v<_Fn>, int> = 0>
constexpr _Ref_fn<_Fn> _Pass_fn(_Fn& _Val) { // pass functor by "reference"
return {_Val};
constexpr auto _Pass_fn(_Fn& _Func) noexcept {
constexpr bool _Pass_by_value = conjunction_v<bool_constant<sizeof(_Fn) <= sizeof(void*)>,
is_trivially_copy_constructible<_Fn>, is_trivially_destructible<_Fn>>;
if constexpr (_Pass_by_value) {
return _Func;
} else {
return _Ref_fn<_Fn>{_Func}; // pass functor by "reference"
}
}

#if _HAS_CXX23
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