source: NonGTP/Boost/boost/utility/enable_if.hpp @ 857

Revision 857, 3.1 KB checked in by igarcia, 19 years ago (diff)
RevLine 
[857]1// Boost enable_if library
2
3// Copyright 2003 © 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 Järvi (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_UTILITY_ENABLE_IF_HPP
15#define BOOST_UTILITY_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 
27  template <bool B, class T = void>
28  struct enable_if_c {
29    typedef T type;
30  };
31
32  template <class T>
33  struct enable_if_c<false, T> {};
34
35  template <class Cond, class T = void>
36  struct enable_if : public enable_if_c<Cond::value, T> {};
37
38  template <bool B, class T>
39  struct lazy_enable_if_c {
40    typedef typename T::type type;
41  };
42
43  template <class T>
44  struct lazy_enable_if_c<false, T> {};
45
46  template <class Cond, class T>
47  struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};
48
49
50  template <bool B, class T = void>
51  struct disable_if_c {
52    typedef T type;
53  };
54
55  template <class T>
56  struct disable_if_c<true, T> {};
57
58  template <class Cond, class T = void>
59  struct disable_if : public disable_if_c<Cond::value, T> {};
60
61  template <bool B, class T>
62  struct lazy_disable_if_c {
63    typedef typename T::type type;
64  };
65
66  template <class T>
67  struct lazy_disable_if_c<true, T> {};
68
69  template <class Cond, class T>
70  struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};
71
72} // namespace boost
73
74#else
75
76namespace boost {
77
78  namespace detail { typedef void enable_if_default_T; }
79
80  template <typename T>
81  struct enable_if_does_not_work_on_this_compiler;
82
83  template <bool B, class T = detail::enable_if_default_T>
84  struct enable_if_c : enable_if_does_not_work_on_this_compiler<T>
85  { };
86
87  template <bool B, class T = detail::enable_if_default_T>
88  struct disable_if_c : enable_if_does_not_work_on_this_compiler<T>
89  { };
90
91  template <bool B, class T = detail::enable_if_default_T>
92  struct lazy_enable_if_c : enable_if_does_not_work_on_this_compiler<T>
93  { };
94
95  template <bool B, class T = detail::enable_if_default_T>
96  struct lazy_disable_if_c : enable_if_does_not_work_on_this_compiler<T>
97  { };
98
99  template <class Cond, class T = detail::enable_if_default_T>
100  struct enable_if : enable_if_does_not_work_on_this_compiler<T>
101  { };
102
103  template <class Cond, class T = detail::enable_if_default_T>
104  struct disable_if : enable_if_does_not_work_on_this_compiler<T>
105  { };
106
107  template <class Cond, class T = detail::enable_if_default_T>
108  struct lazy_enable_if : enable_if_does_not_work_on_this_compiler<T>
109  { };
110
111  template <class Cond, class T = detail::enable_if_default_T>
112  struct lazy_disable_if : enable_if_does_not_work_on_this_compiler<T>
113  { };
114
115} // namespace boost
116
117#endif // BOOST_NO_SFINAE
118
119#endif
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