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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_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 
24 namespace 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 
76 namespace 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
120