    // 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 DLIB_BOOST_UTILITY_ENABLE_IF_HPP
    #define DLIB_BOOST_UTILITY_ENABLE_IF_HPP

    #ifndef BOOST_UTILITY_ENABLE_IF_HPP
    #define BOOST_UTILITY_ENABLE_IF_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 <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 <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 // BOOST_UTILITY_ENABLE_IF_HPP

    namespace dlib
    {
      using boost::enable_if_c;
      using boost::enable_if_c;
      using boost::enable_if;
      using boost::lazy_enable_if_c;
      using boost::lazy_enable_if_c;
      using boost::lazy_enable_if;
      using boost::disable_if_c;
      using boost::disable_if_c;
      using boost::disable_if;
      using boost::lazy_disable_if_c;
      using boost::lazy_disable_if_c;
      using boost::lazy_disable_if;
    }

    #endif // DLIB_BOOST_UTILITY_ENABLE_IF_HPP