1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
|
//===----------------------------------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// <functional>
// reference_wrapper
// has weak result type
#include <functional>
#include <type_traits>
template <class Arg, class Result>
struct my_unary_function
{ // std::unary_function was removed in C++17
typedef Arg argument_type;
typedef Result result_type;
};
template <class Arg1, class Arg2, class Result>
struct my_binary_function
{ // std::binary_function was removed in C++17
typedef Arg1 first_argument_type;
typedef Arg2 second_argument_type;
typedef Result result_type;
};
class functor1
: public my_unary_function<int, char>
{
};
class functor2
: public my_binary_function<char, int, double>
{
};
class functor3
: public my_unary_function<char, int>,
public my_binary_function<char, int, double>
{
public:
typedef float result_type;
};
class functor4
: public my_unary_function<char, int>,
public my_binary_function<char, int, double>
{
public:
};
class C {};
template <class T>
struct has_result_type
{
private:
struct two {char _; char __;};
template <class U> static two test(...);
template <class U> static char test(typename U::result_type* = 0);
public:
static const bool value = sizeof(test<T>(0)) == 1;
};
int main()
{
static_assert((std::is_same<std::reference_wrapper<functor1>::result_type,
char>::value), "");
static_assert((std::is_same<std::reference_wrapper<functor2>::result_type,
double>::value), "");
static_assert((std::is_same<std::reference_wrapper<functor3>::result_type,
float>::value), "");
static_assert((std::is_same<std::reference_wrapper<void()>::result_type,
void>::value), "");
static_assert((std::is_same<std::reference_wrapper<int*(double*)>::result_type,
int*>::value), "");
static_assert((std::is_same<std::reference_wrapper<void(*)()>::result_type,
void>::value), "");
static_assert((std::is_same<std::reference_wrapper<int*(*)(double*)>::result_type,
int*>::value), "");
static_assert((std::is_same<std::reference_wrapper<int*(C::*)(double*)>::result_type,
int*>::value), "");
static_assert((std::is_same<std::reference_wrapper<int (C::*)(double*) const volatile>::result_type,
int>::value), "");
static_assert((std::is_same<std::reference_wrapper<C()>::result_type,
C>::value), "");
static_assert(has_result_type<std::reference_wrapper<functor3> >::value, "");
static_assert(!has_result_type<std::reference_wrapper<functor4> >::value, "");
static_assert(!has_result_type<std::reference_wrapper<C> >::value, "");
}
|
