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[libc++] Add is_nothrow_convertible from P0758R1
Reviewed as https://reviews.llvm.org/D58019. Thanks to Zoe Carver for the patch. llvm-svn: 355010
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‎libcxx/include/type_traits

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@@ -143,7 +143,10 @@ namespace std
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// Relationships between types:
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template <class T, class U> struct is_same;
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template <class Base, class Derived> struct is_base_of;
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template <class From, class To> struct is_convertible;
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template <typename From, typename To> struct is_nothrow_convertible; // C++20
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template <typename From, typename To> inline constexpr bool is_nothrow_convertible_v; // C++20
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template <class Fn, class... ArgTypes> struct is_invocable;
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template <class R, class Fn, class... ArgTypes> struct is_invocable_r;
@@ -1578,6 +1581,32 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_convertible_v
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= is_convertible<_From, _To>::value;
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#endif
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// is_nothrow_convertible
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#if _LIBCPP_STD_VER > 17
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template <typename _Tp>
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static void __test_noexcept(_Tp) noexcept;
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template<typename _Fm, typename _To>
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static bool_constant<noexcept(__test_noexcept<_To>(declval<_Fm>()))>
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__is_nothrow_convertible_test();
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template <typename _Fm, typename _To>
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struct __is_nothrow_convertible_helper: decltype(__is_nothrow_convertible_test<_Fm, _To>())
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{ };
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template <typename _Fm, typename _To>
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struct is_nothrow_convertible : __or_<
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__and_<is_void<_To>, is_void<_Fm>>,
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__and_<is_convertible<_Fm, _To>, __is_nothrow_convertible_helper<_Fm, _To>>
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>::type { };
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template <typename _Fm, typename _To>
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inline constexpr bool is_nothrow_convertible_v = is_nothrow_convertible<_Fm, _To>::value;
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#endif // _LIBCPP_STD_VER > 17
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// is_empty
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#if __has_feature(is_empty) || (_GNUC_VER >= 407)

‎libcxx/test/std/type_traits/is_nothrow_convertible.pass.cpp

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@@ -0,0 +1,58 @@
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// <type_traits>
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// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
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#include <type_traits>
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struct A {};
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struct B {
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public:
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operator A() { return a; } A a;
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};
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class C { };
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class D {
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public:
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operator C() noexcept { return c; } C c;
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};
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int main(int, char**) {
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static_assert((std::is_nothrow_convertible<int, double>::value), "");
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static_assert(!(std::is_nothrow_convertible<int, char*>::value), "");
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static_assert(!(std::is_nothrow_convertible<A, B>::value), "");
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static_assert((std::is_nothrow_convertible<D, C>::value), "");
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static_assert((std::is_nothrow_convertible_v<int, double>), "");
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static_assert(!(std::is_nothrow_convertible_v<int, char*>), "");
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static_assert(!(std::is_nothrow_convertible_v<A, B>), "");
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static_assert((std::is_nothrow_convertible_v<D, C>), "");
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static_assert((std::is_nothrow_convertible_v<const void, void>), "");
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static_assert((std::is_nothrow_convertible_v<volatile void, void>), "");
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static_assert((std::is_nothrow_convertible_v<void, const void>), "");
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static_assert((std::is_nothrow_convertible_v<void, volatile void>), "");
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static_assert(!(std::is_nothrow_convertible_v<int[], double[]>), "");
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static_assert(!(std::is_nothrow_convertible_v<int[], int[]>), "");
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static_assert(!(std::is_nothrow_convertible_v<int[10], int[10]>), "");
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static_assert(!(std::is_nothrow_convertible_v<int[10], double[10]>), "");
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static_assert(!(std::is_nothrow_convertible_v<int[5], double[10]>), "");
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static_assert(!(std::is_nothrow_convertible_v<int[10], A[10]>), "");
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typedef void V();
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typedef int I();
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static_assert(!(std::is_nothrow_convertible_v<V, V>), "");
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static_assert(!(std::is_nothrow_convertible_v<V, I>), "");
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return 0;
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}

‎libcxx/www/cxx2a_status.html

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@@ -92,7 +92,7 @@ <h3>Paper Status</h3>
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<tr><td><a href="https://wg21.link/P0619R4">P0619R4</a></td><td>LWG</td><td>Reviewing Deprecated Facilities of C++17 for C++20</td><td>Rapperswil</td><td></td><td></td></tr>
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<tr><td><a href="https://wg21.link/P0646R1">P0646R1</a></td><td>LWG</td><td>Improving the Return Value of Erase-Like Algorithms</td><td>Rapperswil</td><td></td><td></td></tr>
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<tr><td><a href="https://wg21.link/P0722R3">P0722R3</a></td><td>CWG</td><td>Efficient sized delete for variable sized classes</td><td>Rapperswil</td><td></td><td></td></tr>
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<tr><td><a href="https://wg21.link/P0758R1">P0758R1</a></td><td>LWG</td><td>Implicit conversion traits and utility functions</td><td>Rapperswil</td><td></td><td></td></tr>
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<tr><td><a href="https://wg21.link/P0758R1">P0758R1</a></td><td>LWG</td><td>Implicit conversion traits and utility functions</td><td>Rapperswil</td><td>Complete</td><td></td></tr>
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<tr><td><a href="https://wg21.link/P0759R1">P0759R1</a></td><td>LWG</td><td>fpos Requirements</td><td>Rapperswil</td><td></td><td></td></tr>
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<tr><td><a href="https://wg21.link/P0769R2">P0769R2</a></td><td>LWG</td><td>Add shift to &lt;algorithm&gt;</td><td>Rapperswil</td><td></td><td></td></tr>
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<tr><td><a href="https://wg21.link/P0788R3">P0788R3</a></td><td>LWG</td><td>Standard Library Specification in a Concepts and Contracts World</td><td>Rapperswil</td><td></td><td></td></tr>

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