84 lines · cpp
1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9// <functional>10 11// namespace placeholders {12// // M is the implementation-defined number of placeholders13// extern unspecified _1;14// extern unspecified _2;15// .16// .17// .18// extern unspecified _Mp;19// }20 21// The Standard recommends implementing them as `inline constexpr` in C++17.22//23// Libc++ implements the placeholders as `extern const` in all standard modes24// to avoid an ABI break in C++03: making them `inline constexpr` requires removing25// their definition in the shared library to avoid ODR violations, which is an26// ABI break.27//28// Concretely, `extern const` is almost indistinguishable from constexpr for the29// placeholders since they are empty types.30 31#include <functional>32#include <type_traits>33 34#include "test_macros.h"35 36template <class T>37TEST_CONSTEXPR_CXX17 void test(const T& t) {38 // Test default constructible.39 {40 T x; (void)x;41 }42 43 // Test copy constructible.44 {45 T x = t; (void)x;46 static_assert(std::is_nothrow_copy_constructible<T>::value, "");47 static_assert(std::is_nothrow_move_constructible<T>::value, "");48 }49 50 // It is implementation-defined whether placeholder types are CopyAssignable.51 // CopyAssignable placeholders' copy assignment operators shall not throw exceptions.52#ifdef _LIBCPP_VERSION53 {54 T x;55 x = t;56 static_assert(std::is_nothrow_copy_assignable<T>::value, "");57 static_assert(std::is_nothrow_move_assignable<T>::value, "");58 }59#endif60}61 62TEST_CONSTEXPR_CXX17 bool test_all() {63 test(std::placeholders::_1);64 test(std::placeholders::_2);65 test(std::placeholders::_3);66 test(std::placeholders::_4);67 test(std::placeholders::_5);68 test(std::placeholders::_6);69 test(std::placeholders::_7);70 test(std::placeholders::_8);71 test(std::placeholders::_9);72 test(std::placeholders::_10);73 return true;74}75 76int main(int, char**) {77 test_all();78#if TEST_STD_VER >= 1779 static_assert(test_all(), "");80#endif81 82 return 0;83}84