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-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 // <functional>
10
11 // namespace placeholders {
12 // // M is the implementation-defined number of placeholders
13 // 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 modes
24 // to avoid an ABI break in C++03: making them `inline constexpr` requires removing
25 // their definition in the shared library to avoid ODR violations, which is an
26 // ABI break.
27 //
28 // Concretely, `extern const` is almost indistinguishable from constexpr for the
29 // placeholders since they are empty types.
30
31 #include <functional>
32 #include <type_traits>
33
34 #include "test_macros.h"
35
36 template <class T>
test(const T & t)37 TEST_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_VERSION
53 {
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 #endif
60 }
61
test_all()62 TEST_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
main(int,char **)76 int main(int, char**) {
77 test_all();
78 #if TEST_STD_VER >= 17
79 static_assert(test_all(), "");
80 #endif
81
82 return 0;
83 }
84