1// Boost enable_if library
2
3// Copyright 2003 (c) The Trustees of Indiana University.
4
5// Use, modification, and distribution is subject to the Boost Software
6// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
7// http://www.boost.org/LICENSE_1_0.txt)
8
9// Authors: Jaakko Jarvi (jajarvi at osl.iu.edu)
10// Jeremiah Willcock (jewillco at osl.iu.edu)
11// Andrew Lumsdaine (lums at osl.iu.edu)
12
13
14#ifndef BOOST_CORE_ENABLE_IF_HPP
15#define BOOST_CORE_ENABLE_IF_HPP
16
17#include "boost/config.hpp"
18
19// Even the definition of enable_if causes problems on some compilers,
20// so it's macroed out for all compilers that do not support SFINAE
21
22#ifndef BOOST_NO_SFINAE
23
24namespace boost
25{
26 template<typename T, typename R=void>
27 struct enable_if_has_type
28 {
29 typedef R type;
30 };
31
32 template <bool B, class T = void>
33 struct enable_if_c {
34 typedef T type;
35 };
36
37 template <class T>
38 struct enable_if_c<false, T> {};
39
40 template <class Cond, class T = void>
41 struct enable_if : public enable_if_c<Cond::value, T> {};
42
43 template <bool B, class T>
44 struct lazy_enable_if_c {
45 typedef typename T::type type;
46 };
47
48 template <class T>
49 struct lazy_enable_if_c<false, T> {};
50
51 template <class Cond, class T>
52 struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};
53
54
55 template <bool B, class T = void>
56 struct disable_if_c {
57 typedef T type;
58 };
59
60 template <class T>
61 struct disable_if_c<true, T> {};
62
63 template <class Cond, class T = void>
64 struct disable_if : public disable_if_c<Cond::value, T> {};
65
66 template <bool B, class T>
67 struct lazy_disable_if_c {
68 typedef typename T::type type;
69 };
70
71 template <class T>
72 struct lazy_disable_if_c<true, T> {};
73
74 template <class Cond, class T>
75 struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};
76
77} // namespace boost
78
79#else
80
81namespace boost {
82
83 namespace detail { typedef void enable_if_default_T; }
84
85 template <typename T>
86 struct enable_if_does_not_work_on_this_compiler;
87
88 template<typename T, typename R=void>
89 struct enable_if_has_type : enable_if_does_not_work_on_this_compiler<T>
90 { };
91
92 template <bool B, class T = detail::enable_if_default_T>
93 struct enable_if_c : enable_if_does_not_work_on_this_compiler<T>
94 { };
95
96 template <bool B, class T = detail::enable_if_default_T>
97 struct disable_if_c : enable_if_does_not_work_on_this_compiler<T>
98 { };
99
100 template <bool B, class T = detail::enable_if_default_T>
101 struct lazy_enable_if_c : enable_if_does_not_work_on_this_compiler<T>
102 { };
103
104 template <bool B, class T = detail::enable_if_default_T>
105 struct lazy_disable_if_c : enable_if_does_not_work_on_this_compiler<T>
106 { };
107
108 template <class Cond, class T = detail::enable_if_default_T>
109 struct enable_if : enable_if_does_not_work_on_this_compiler<T>
110 { };
111
112 template <class Cond, class T = detail::enable_if_default_T>
113 struct disable_if : enable_if_does_not_work_on_this_compiler<T>
114 { };
115
116 template <class Cond, class T = detail::enable_if_default_T>
117 struct lazy_enable_if : enable_if_does_not_work_on_this_compiler<T>
118 { };
119
120 template <class Cond, class T = detail::enable_if_default_T>
121 struct lazy_disable_if : enable_if_does_not_work_on_this_compiler<T>
122 { };
123
124} // namespace boost
125
126#endif // BOOST_NO_SFINAE
127
128#endif
129

source code of include/boost/core/enable_if.hpp