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 24 namespace 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 81 namespace 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