text: ///////////////////////////////////////////////////////////////////////////////
  /// \file as_expr.hpp
  /// Contains definition of the as_expr\<\> and as_child\<\> helper class
  /// templates used to implement proto::domain's as_expr\<\> and as_child\<\>
  /// member templates.
  //
  //  Copyright 2010 Eric Niebler. Distributed under 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)
  
  #ifndef BOOST_PROTO_DETAIL_AS_EXPR_HPP_EAN_06_09_2010
  #define BOOST_PROTO_DETAIL_AS_EXPR_HPP_EAN_06_09_2010
  
  #include <boost/config.hpp>
  #include <boost/detail/workaround.hpp>
  #include <boost/type_traits/remove_const.hpp>
  #include <boost/proto/proto_fwd.hpp>
  #include <boost/proto/args.hpp>
  
  namespace boost { namespace proto { namespace detail
  {
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename Generator>
      struct base_generator
      {
          typedef Generator type;
      };
  
      template<typename Generator>
      struct base_generator<use_basic_expr<Generator> >
      {
          typedef Generator type;
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T, typename Generator, bool WantsBasicExpr>
      struct as_expr;
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T, typename Generator>
      struct as_expr<T, Generator, false>
      {
          typedef typename term_traits<T &>::value_type value_type;
          typedef proto::expr<proto::tag::terminal, term<value_type>, 0> expr_type;
          typedef typename Generator::template result<Generator(expr_type)>::type result_type;
  
          result_type operator()(T &t) const
          {
              return Generator()(expr_type::make(t));
          }
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T, typename Generator>
      struct as_expr<T, Generator, true>
      {
          typedef typename term_traits<T &>::value_type value_type;
          typedef proto::basic_expr<proto::tag::terminal, term<value_type>, 0> expr_type;
          typedef typename Generator::template result<Generator(expr_type)>::type result_type;
  
          result_type operator()(T &t) const
          {
              return Generator()(expr_type::make(t));
          }
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T>
      struct as_expr<T, proto::default_generator, false>
      {
          typedef typename term_traits<T &>::value_type value_type;
          typedef proto::expr<proto::tag::terminal, term<value_type>, 0> result_type;
  
          result_type operator()(T &t) const
          {
              return result_type::make(t);
          }
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T>
      struct as_expr<T, proto::default_generator, true>
      {
          typedef typename term_traits<T &>::value_type value_type;
          typedef proto::basic_expr<proto::tag::terminal, term<value_type>, 0> result_type;
  
          result_type operator()(T &t) const
          {
              return result_type::make(t);
          }
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T, typename Generator, bool WantsBasicExpr>
      struct as_child;
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T, typename Generator>
      struct as_child<T, Generator, false>
      {
      #if BOOST_WORKAROUND(BOOST_MSVC, == 1310)
          typedef typename term_traits<T &>::reference reference;
      #else
          typedef T &reference;
      #endif
          typedef proto::expr<proto::tag::terminal, term<reference>, 0> expr_type;
          typedef typename Generator::template result<Generator(expr_type)>::type result_type;
  
          result_type operator()(T &t) const
          {
              return Generator()(expr_type::make(t));
          }
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T, typename Generator>
      struct as_child<T, Generator, true>
      {
      #if BOOST_WORKAROUND(BOOST_MSVC, == 1310)
          typedef typename term_traits<T &>::reference reference;
      #else
          typedef T &reference;
      #endif
          typedef proto::basic_expr<proto::tag::terminal, term<reference>, 0> expr_type;
          typedef typename Generator::template result<Generator(expr_type)>::type result_type;
  
          result_type operator()(T &t) const
          {
              return Generator()(expr_type::make(t));
          }
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T>
      struct as_child<T, proto::default_generator, false>
      {
      #if BOOST_WORKAROUND(BOOST_MSVC, == 1310)
          typedef typename term_traits<T &>::reference reference;
      #else
          typedef T &reference;
      #endif
          typedef proto::expr<proto::tag::terminal, term<reference>, 0> result_type;
  
          result_type operator()(T &t) const
          {
              return result_type::make(t);
          }
      };
  
      ////////////////////////////////////////////////////////////////////////////////////////////////
      template<typename T>
      struct as_child<T, proto::default_generator, true>
      {
      #if BOOST_WORKAROUND(BOOST_MSVC, == 1310)
          typedef typename term_traits<T &>::reference reference;
      #else
          typedef T &reference;
      #endif
          typedef proto::basic_expr<proto::tag::terminal, term<reference>, 0> result_type;
  
          result_type operator()(T &t) const
          {
              return result_type::make(t);
          }
      };
  
  }}}
  
  #endif
  