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