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<type_traits>: Make is_nothrow_convertible a class template and ADL-proof #4318

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Jan 17, 2024
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<type_traits>: Make is_nothrow_convertible a class template and ADL-proof #4318

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34a9c14
Make `is_nothrow_convertible` a class template and ADL-proof
frederick-vs-ja Jan 15, 2024
4b2cbb5
Skip `_M_CEE` for tests for incomplete types
frederick-vs-ja Jan 15, 2024
e50a400
Fix grammar mistake in bug title.
StephanTLavavej Jan 16, 2024
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4 changes: 2 additions & 2 deletions stl/inc/type_traits
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Original file line number Diff line number Diff line change
Expand Up @@ -1764,7 +1764,7 @@ constexpr auto invoke(_Callable&& _Obj, _Ty1&& _Arg1, _Types2&&... _Args2) noexc
#pragma warning(disable : 4365) // '%s': conversion from '%s' to '%s', signed/unsigned mismatch (/Wall)

template <class _From, class _To, bool = is_convertible_v<_From, _To>, bool = is_void_v<_To>>
_INLINE_VAR constexpr bool _Is_nothrow_convertible_v = noexcept(_Fake_copy_init<_To>(_STD declval<_From>()));
_INLINE_VAR constexpr bool _Is_nothrow_convertible_v = noexcept(_STD _Fake_copy_init<_To>(_STD declval<_From>()));

#pragma warning(pop)

Expand All @@ -1784,7 +1784,7 @@ _EXPORT_STD template <class _From, class _To>
inline constexpr bool is_nothrow_convertible_v = _Is_nothrow_convertible_v<_From, _To>;

_EXPORT_STD template <class _From, class _To>
using is_nothrow_convertible = _Is_nothrow_convertible<_From, _To>;
struct is_nothrow_convertible : bool_constant<_Is_nothrow_convertible_v<_From, _To>> {};
#endif // _HAS_CXX20

template <class _From, class _To, class = void>
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27 changes: 27 additions & 0 deletions tests/std/tests/P0758R1_is_nothrow_convertible/test.compile.pass.cpp
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Expand Up @@ -105,5 +105,32 @@ STATIC_ASSERT(is_nothrow_convertible_v<int[1], int*>);
STATIC_ASSERT(!is_nothrow_convertible_v<int[], int[]>);
STATIC_ASSERT(!is_nothrow_convertible_v<int[], int[1]>);

// Also test GH-4317 <type_traits>: some traits are an aliases and fail when used with parameter pack
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template <class... Ts>
using aliased_is_nothrow_convertible = is_nothrow_convertible<Ts...>;

template <class T, template <class...> class Tmpl>
constexpr bool is_specialization_of_v = false;
template <class... Ts, template <class...> class Tmpl>
constexpr bool is_specialization_of_v<Tmpl<Ts...>, Tmpl> = true;

STATIC_ASSERT(is_specialization_of_v<is_nothrow_convertible<void, void>, is_nothrow_convertible>);
STATIC_ASSERT(!is_specialization_of_v<aliased_is_nothrow_convertible<void, void>, aliased_is_nothrow_convertible>);

#ifndef _M_CEE // TRANSITION, VSO-1659496
// Also test that is_nothrow_convertible/is_nothrow_convertible_v are ADL-proof

template <class T>
struct holder {
T t;
};

struct incomplete;

STATIC_ASSERT(is_nothrow_convertible<holder<incomplete>*, holder<incomplete>*>::value);
STATIC_ASSERT(is_nothrow_convertible_v<holder<incomplete>*, holder<incomplete>*>);
#endif // _M_CEE

// VSO_0105317_expression_sfinae and VSO_0000000_type_traits provide
// additional coverage of this machinery