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