williamr@2: // Boost enable_if library
williamr@2: 
williamr@2: // Copyright 2003 © The Trustees of Indiana University.
williamr@2: 
williamr@2: // Use, modification, and distribution is subject to the Boost Software
williamr@2: // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
williamr@2: // http://www.boost.org/LICENSE_1_0.txt)
williamr@2: 
williamr@2: //    Authors: Jaakko Järvi (jajarvi at osl.iu.edu)
williamr@2: //             Jeremiah Willcock (jewillco at osl.iu.edu)
williamr@2: //             Andrew Lumsdaine (lums at osl.iu.edu)
williamr@2: 
williamr@2: 
williamr@2: #ifndef BOOST_UTILITY_ENABLE_IF_HPP
williamr@2: #define BOOST_UTILITY_ENABLE_IF_HPP
williamr@2: 
williamr@2: #include "boost/config.hpp"
williamr@2: 
williamr@2: // Even the definition of enable_if causes problems on some compilers,
williamr@2: // so it's macroed out for all compilers that do not support SFINAE
williamr@2: 
williamr@2: #ifndef BOOST_NO_SFINAE
williamr@2: 
williamr@2: namespace boost
williamr@2: {
williamr@2:  
williamr@2:   template <bool B, class T = void>
williamr@2:   struct enable_if_c {
williamr@2:     typedef T type;
williamr@2:   };
williamr@2: 
williamr@2:   template <class T>
williamr@2:   struct enable_if_c<false, T> {};
williamr@2: 
williamr@2:   template <class Cond, class T = void> 
williamr@2:   struct enable_if : public enable_if_c<Cond::value, T> {};
williamr@2: 
williamr@2:   template <bool B, class T>
williamr@2:   struct lazy_enable_if_c {
williamr@2:     typedef typename T::type type;
williamr@2:   };
williamr@2: 
williamr@2:   template <class T>
williamr@2:   struct lazy_enable_if_c<false, T> {};
williamr@2: 
williamr@2:   template <class Cond, class T> 
williamr@2:   struct lazy_enable_if : public lazy_enable_if_c<Cond::value, T> {};
williamr@2: 
williamr@2: 
williamr@2:   template <bool B, class T = void>
williamr@2:   struct disable_if_c {
williamr@2:     typedef T type;
williamr@2:   };
williamr@2: 
williamr@2:   template <class T>
williamr@2:   struct disable_if_c<true, T> {};
williamr@2: 
williamr@2:   template <class Cond, class T = void> 
williamr@2:   struct disable_if : public disable_if_c<Cond::value, T> {};
williamr@2: 
williamr@2:   template <bool B, class T>
williamr@2:   struct lazy_disable_if_c {
williamr@2:     typedef typename T::type type;
williamr@2:   };
williamr@2: 
williamr@2:   template <class T>
williamr@2:   struct lazy_disable_if_c<true, T> {};
williamr@2: 
williamr@2:   template <class Cond, class T> 
williamr@2:   struct lazy_disable_if : public lazy_disable_if_c<Cond::value, T> {};
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #else
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2:   namespace detail { typedef void enable_if_default_T; }
williamr@2: 
williamr@2:   template <typename T>
williamr@2:   struct enable_if_does_not_work_on_this_compiler;
williamr@2: 
williamr@2:   template <bool B, class T = detail::enable_if_default_T>
williamr@2:   struct enable_if_c : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2:   template <bool B, class T = detail::enable_if_default_T> 
williamr@2:   struct disable_if_c : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2:   template <bool B, class T = detail::enable_if_default_T> 
williamr@2:   struct lazy_enable_if_c : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2:   template <bool B, class T = detail::enable_if_default_T> 
williamr@2:   struct lazy_disable_if_c : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2:   template <class Cond, class T = detail::enable_if_default_T> 
williamr@2:   struct enable_if : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2:   template <class Cond, class T = detail::enable_if_default_T> 
williamr@2:   struct disable_if : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2:   template <class Cond, class T = detail::enable_if_default_T> 
williamr@2:   struct lazy_enable_if : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2:   template <class Cond, class T = detail::enable_if_default_T> 
williamr@2:   struct lazy_disable_if : enable_if_does_not_work_on_this_compiler<T>
williamr@2:   { };
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #endif // BOOST_NO_SFINAE
williamr@2: 
williamr@2: #endif