identity.hpp
1.22 KB
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
/*
Copyright 2021 Glen Joseph Fernandes
(glenjofe@gmail.com)
Distributed under the Boost Software License, Version 1.0.
(http://www.boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_FUNCTIONAL_IDENTITY_HPP
#define BOOST_FUNCTIONAL_IDENTITY_HPP
#include <boost/config.hpp>
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#include <utility>
#endif
namespace boost {
struct identity {
typedef void is_transparent;
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
template<class T>
BOOST_CONSTEXPR T&& operator()(T&& value) const BOOST_NOEXCEPT {
return std::forward<T>(value);
}
#else
template<class T>
BOOST_CONSTEXPR const T& operator()(const T& value) const BOOST_NOEXCEPT {
return value;
}
template<class T>
BOOST_CONSTEXPR T& operator()(T& value) const BOOST_NOEXCEPT {
return value;
}
#endif
template<class>
struct result { };
template<class T>
struct result<identity(T&)> {
typedef T& type;
};
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
template<class T>
struct result<identity(T)> {
typedef T&& type;
};
template<class T>
struct result<identity(T&&)> {
typedef T&& type;
};
#endif
};
} // boost
#endif