deps/boost_1_63_0/boost/core/enable_if.hpp

   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