core/enable_if.hpp

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// Boost enable_if library
 
// Copyright 2003 (c) The Trustees of Indiana University.
 
// Use, modification, and distribution is subject to the Boost Software
// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
 
//    Authors: Jaakko Jarvi (jajarvi at osl.iu.edu)
//             Jeremiah Willcock (jewillco at osl.iu.edu)
//             Andrew Lumsdaine (lums at osl.iu.edu)
 
 
#ifndef BOOST_CORE_ENABLE_IF_HPP
#define BOOST_CORE_ENABLE_IF_HPP
 
#include "boost/config.hpp"
 
// Even the definition of enable_if causes problems on some compilers,
// so it's macroed out for all compilers that do not support SFINAE
 
#ifndef BOOST_NO_SFINAE
 
namespace boost
{
  template<typename T, typename R=void>
  struct enable_if_has_type
  {
    typedef R type;
  };
 
  template <bool B, class T = void>
  struct enable_if_c {
    typedef T type;
  };
 
  template <class T>
  struct enable_if_c<false, T> {};
 
  template <class Cond, class T = void> 
  struct enable_if : public enable_if_c<Cond::value, T> {};
 
  template <bool B, class T>
  struct lazy_enable_if_c {
    typedef typename T::type type;
  };
 
  template <class T>
  struct lazy_enable_if_c<false, T> {};
 
  template <class Cond, class T> 
  struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};
 
 
  template <bool B, class T = void>
  struct disable_if_c {
    typedef T type;
  };
 
  template <class T>
  struct disable_if_c<true, T> {};
 
  template <class Cond, class T = void> 
  struct disable_if : public disable_if_c<Cond::value, T> {};
 
  template <bool B, class T>
  struct lazy_disable_if_c {
    typedef typename T::type type;
  };
 
  template <class T>
  struct lazy_disable_if_c<true, T> {};
 
  template <class Cond, class T> 
  struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};
 
} // namespace boost
 
#else
 
namespace boost {
 
  namespace detail { typedef void enable_if_default_T; }
 
  template <typename T>
  struct enable_if_does_not_work_on_this_compiler;
 
  template<typename T, typename R=void>
  struct enable_if_has_type : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <bool B, class T = detail::enable_if_default_T>
  struct enable_if_c : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <bool B, class T = detail::enable_if_default_T> 
  struct disable_if_c : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <bool B, class T = detail::enable_if_default_T> 
  struct lazy_enable_if_c : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <bool B, class T = detail::enable_if_default_T> 
  struct lazy_disable_if_c : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <class Cond, class T = detail::enable_if_default_T> 
  struct enable_if : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <class Cond, class T = detail::enable_if_default_T> 
  struct disable_if : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <class Cond, class T = detail::enable_if_default_T> 
  struct lazy_enable_if : enable_if_does_not_work_on_this_compiler<T>
  { };
 
  template <class Cond, class T = detail::enable_if_default_T> 
  struct lazy_disable_if : enable_if_does_not_work_on_this_compiler<T>
  { };
 
} // namespace boost
 
#endif // BOOST_NO_SFINAE
 
#endif