Chris@16: //  boost/identifier.hpp  ----------------------------------------------------//
Chris@16: 
Chris@16: //  Copyright Beman Dawes 2006
Chris@16: 
Chris@16: //  Distributed under the Boost Software License, Version 1.0. (See accompanying
Chris@16: //  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: //  See documentation at http://www.boost.org/libs/utility
Chris@16: 
Chris@16: #ifndef BOOST_IDENTIFIER_HPP
Chris@16: #define BOOST_IDENTIFIER_HPP
Chris@16: 
Chris@16: #include <boost/utility/enable_if.hpp>
Chris@16: #include <boost/type_traits/is_base_of.hpp>
Chris@16: #include <iosfwd>
Chris@16: 
Chris@16: namespace boost
Chris@16: {
Chris@16:   namespace detail
Chris@16:   {
Chris@16:     //  class template identifier  ---------------------------------------------//
Chris@16: 
Chris@16:     //  Always used as a base class so that different instantiations result in
Chris@16:     //  different class types even if instantiated with the same value type T.
Chris@16: 
Chris@16:     //  Expected usage is that T is often an integer type, best passed by
Chris@16:     //  value. There is no reason why T can't be a possibly larger class such as
Chris@16:     //  std::string, best passed by const reference.
Chris@16: 
Chris@16:     //  This implementation uses pass by value, based on expected common uses.
Chris@16: 
Chris@16:     template <typename T, typename D>
Chris@16:     class identifier
Chris@16:     {
Chris@16:     public:
Chris@16:       typedef T value_type;
Chris@16: 
Chris@16:       const value_type value() const           { return m_value; }
Chris@16:       void  assign( value_type v )             { m_value = v; }
Chris@16: 
Chris@16:       bool operator==( const D & rhs ) const   { return m_value == rhs.m_value; }
Chris@16:       bool operator!=( const D & rhs ) const   { return m_value != rhs.m_value; }
Chris@16:       bool operator< ( const D & rhs ) const   { return m_value <  rhs.m_value; }
Chris@16:       bool operator<=( const D & rhs ) const   { return m_value <= rhs.m_value; }
Chris@16:       bool operator> ( const D & rhs ) const   { return m_value >  rhs.m_value; }
Chris@16:       bool operator>=( const D & rhs ) const   { return m_value >= rhs.m_value; }
Chris@16: 
Chris@16:       typedef void (*unspecified_bool_type)(D); // without the D, unspecified_bool_type 
Chris@16:       static void unspecified_bool_true(D){}    // conversion allows relational operators
Chris@16:                                                 // between different identifier types
Chris@16: 
Chris@16:       operator unspecified_bool_type() const   { return m_value == value_type() ? 0 : unspecified_bool_true; }
Chris@16:       bool operator!() const                   { return m_value == value_type(); }
Chris@16: 
Chris@16:     // constructors are protected so that class can only be used as a base class
Chris@16:     protected:
Chris@16:       identifier()                             {}
Chris@16:       explicit identifier( value_type v )      : m_value(v) {}
Chris@16: 
Chris@16:     private:
Chris@16:       T m_value;
Chris@16:     };
Chris@16: 
Chris@16:   //#ifndef BOOST_NO_SFINAE
Chris@16: 
Chris@16:   //  template <class Ostream, class Id>
Chris@16:   //    typename enable_if< is_base_of< identifier< typename Id::value_type, Id >, Id >, 
Chris@16:   //      Ostream & >::type operator<<( Ostream & os, const Id & id )
Chris@16:   //  {
Chris@16:   //    return os << id.value();
Chris@16:   //  }
Chris@16: 
Chris@16:   //  template <class Istream, class Id>
Chris@16:   //    typename enable_if< is_base_of< identifier< typename Id::value_type, Id >, Id >, 
Chris@16:   //      Istream & >::type operator>>( Istream & is, Id & id )
Chris@16:   //  {
Chris@16:   //    typename Id::value_type v;
Chris@16:   //    is >> v;
Chris@16:   //    id.value( v );
Chris@16:   //    return is;
Chris@16:   //  }
Chris@16:   //#endif
Chris@16: 
Chris@16:   } // namespace detail
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #endif // BOOST_IDENTIFIER_HPP