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 // reference_wrapper
12 
13 // has weak result type
14 
15 #include <functional>
16 #include <type_traits>
17 
18 template <class Arg, class Result>
19 struct my_unary_function
20 { // std::unary_function was removed in C++17
21     typedef Arg argument_type;
22     typedef Result result_type;
23 };
24 
25 template <class Arg1, class Arg2, class Result>
26 struct my_binary_function
27 { // std::binary_function was removed in C++17
28     typedef Arg1 first_argument_type;
29     typedef Arg2 second_argument_type;
30     typedef Result result_type;
31 };
32 
33 class functor1
34     : public my_unary_function<int, char>
35 {
36 };
37 
38 class functor2
39     : public my_binary_function<char, int, double>
40 {
41 };
42 
43 class functor3
44     : public my_unary_function<char, int>,
45       public my_binary_function<char, int, double>
46 {
47 public:
48     typedef float result_type;
49 };
50 
51 class functor4
52     : public my_unary_function<char, int>,
53       public my_binary_function<char, int, double>
54 {
55 public:
56 };
57 
58 class C {};
59 
60 template <class T>
61 struct has_result_type
62 {
63 private:
64     struct two {char _; char __;};
65     template <class U> static two test(...);
66     template <class U> static char test(typename U::result_type* = 0);
67 public:
68     static const bool value = sizeof(test<T>(0)) == 1;
69 };
70 
71 int main(int, char**)
72 {
73     static_assert((std::is_same<std::reference_wrapper<functor1>::result_type,
74                                 char>::value), "");
75     static_assert((std::is_same<std::reference_wrapper<functor2>::result_type,
76                                 double>::value), "");
77     static_assert((std::is_same<std::reference_wrapper<functor3>::result_type,
78                                 float>::value), "");
79     static_assert((std::is_same<std::reference_wrapper<void()>::result_type,
80                                 void>::value), "");
81     static_assert((std::is_same<std::reference_wrapper<int*(double*)>::result_type,
82                                 int*>::value), "");
83     static_assert((std::is_same<std::reference_wrapper<void(*)()>::result_type,
84                                 void>::value), "");
85     static_assert((std::is_same<std::reference_wrapper<int*(*)(double*)>::result_type,
86                                 int*>::value), "");
87     static_assert((std::is_same<std::reference_wrapper<int*(C::*)(double*)>::result_type,
88                                 int*>::value), "");
89     static_assert((std::is_same<std::reference_wrapper<int (C::*)(double*) const volatile>::result_type,
90                                 int>::value), "");
91     static_assert((std::is_same<std::reference_wrapper<C()>::result_type,
92                                 C>::value), "");
93     static_assert(has_result_type<std::reference_wrapper<functor3> >::value, "");
94     static_assert(!has_result_type<std::reference_wrapper<functor4> >::value, "");
95     static_assert(!has_result_type<std::reference_wrapper<C> >::value, "");
96 
97   return 0;
98 }
99