Boost C++ Libraries

boost/blank.hpp

//-----------------------------------------------------------------------------
// boost blank.hpp header file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 2003
// Eric Friedman
//
// Permission to use, copy, modify, distribute and sell this software
// and its documentation for any purpose is hereby granted without fee, 
// provided that the above copyright notice appears in all copies and 
// that both the copyright notice and this permission notice appear in 
// supporting documentation. No representations are made about the 
// suitability of this software for any purpose. It is provided "as is" 
// without express or implied warranty.

#ifndef BOOST_BLANK_HPP
#define BOOST_BLANK_HPP

#include "boost/blank_fwd.hpp"

#include <iosfwd> // for std::basic_ostream forward declare

#include "boost/detail/templated_streams.hpp"
#include "boost/mpl/bool.hpp"
#include "boost/type_traits/is_empty.hpp"
#include "boost/type_traits/is_pod.hpp"
#include "boost/type_traits/is_stateless.hpp"

namespace boost {

struct blank
{
};

// type traits specializations
//

template <>
struct is_pod< blank >
    : mpl::true_
{
};

template <>
struct is_empty< blank >
    : mpl::true_
{
};

template <>
struct is_stateless< blank >
    : mpl::true_
{
};

// relational operators
//

inline bool operator==(const blank&, const blank&)
{
    return true;
}

inline bool operator<(const blank&, const blank&)
{
    return false;
}

// streaming support
//
BOOST_TEMPLATED_STREAM_TEMPLATE(E,T)
inline BOOST_TEMPLATED_STREAM(ostream, E,T)& operator<<(
      BOOST_TEMPLATED_STREAM(ostream, E,T)& out
    , const blank&
    )
{
    // (output nothing)
    return out;
}

} // namespace boost

#endif // BOOST_BLANK_HPP