63e88f80
 Hu Chunming
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// boost/identifier.hpp ----------------------------------------------------//
// Copyright Beman Dawes 2006
// 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)
// See documentation at http://www.boost.org/libs/utility
#ifndef BOOST_IDENTIFIER_HPP
#define BOOST_IDENTIFIER_HPP
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_base_of.hpp>
#include <iosfwd>
namespace boost
{
namespace detail
{
// class template identifier ---------------------------------------------//
// Always used as a base class so that different instantiations result in
// different class types even if instantiated with the same value type T.
// Expected usage is that T is often an integer type, best passed by
// value. There is no reason why T can't be a possibly larger class such as
// std::string, best passed by const reference.
// This implementation uses pass by value, based on expected common uses.
template <typename T, typename D>
class identifier
{
public:
typedef T value_type;
const value_type value() const { return m_value; }
void assign( value_type v ) { m_value = v; }
bool operator==( const D & rhs ) const { return m_value == rhs.m_value; }
bool operator!=( const D & rhs ) const { return m_value != rhs.m_value; }
bool operator< ( const D & rhs ) const { return m_value < rhs.m_value; }
bool operator<=( const D & rhs ) const { return m_value <= rhs.m_value; }
bool operator> ( const D & rhs ) const { return m_value > rhs.m_value; }
bool operator>=( const D & rhs ) const { return m_value >= rhs.m_value; }
typedef void (*unspecified_bool_type)(D); // without the D, unspecified_bool_type
static void unspecified_bool_true(D){} // conversion allows relational operators
// between different identifier types
operator unspecified_bool_type() const { return m_value == value_type() ? 0 : unspecified_bool_true; }
bool operator!() const { return m_value == value_type(); }
// constructors are protected so that class can only be used as a base class
protected:
identifier() {}
explicit identifier( value_type v ) : m_value(v) {}
private:
T m_value;
};
//#ifndef BOOST_NO_SFINAE
// template <class Ostream, class Id>
// typename enable_if< is_base_of< identifier< typename Id::value_type, Id >, Id >,
// Ostream & >::type operator<<( Ostream & os, const Id & id )
// {
// return os << id.value();
// }
// template <class Istream, class Id>
// typename enable_if< is_base_of< identifier< typename Id::value_type, Id >, Id >,
// Istream & >::type operator>>( Istream & is, Id & id )
// {
// typename Id::value_type v;
// is >> v;
// id.value( v );
// return is;
// }
//#endif
} // namespace detail
} // namespace boost
#endif // BOOST_IDENTIFIER_HPP
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