apply_visitor_unary.hpp

C++的一个好库。。。现在很流行

//-----------------------------------------------------------------------------
// boost variant/detail/apply_visitor_unary.hpp header file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 2002-2003
// Eric Friedman
//
// 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_VARIANT_DETAIL_APPLY_VISITOR_UNARY_HPP
#define BOOST_VARIANT_DETAIL_APPLY_VISITOR_UNARY_HPP

#include "boost/config.hpp"
#include "boost/detail/workaround.hpp"
#include "boost/variant/detail/generic_result_type.hpp"

#include "boost/utility/enable_if.hpp"

namespace boost {

//////////////////////////////////////////////////////////////////////////
// function template apply_visitor(visitor, visitable)
//
// Visits visitable with visitor.
//

//
// nonconst-visitor version:
//

#if !BOOST_WORKAROUND(__EDG__, BOOST_TESTED_AT(302))

#   define BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE(V) \
    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename V::result_type) \
    /**/

#else // EDG-based compilers

#   define BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE(V) \
    typename enable_if< \
          mpl::not_< is_const< V > > \
        , BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename V::result_type) \
        >::type \
    /**/

#endif // EDG-based compilers workaround

template <typename Visitor, typename Visitable>
inline
    BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE(Visitor)
apply_visitor(Visitor& visitor, Visitable& visitable)
{
    return visitable.apply_visitor(visitor);
}

#undef BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE

//
// const-visitor version:
//

#if !BOOST_WORKAROUND(BOOST_MSVC, <= 1300)

template <typename Visitor, typename Visitable>
inline
    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
apply_visitor(const Visitor& visitor, Visitable& visitable)
{
    return visitable.apply_visitor(visitor);
}

#endif // MSVC7 and below exclusion

} // namespace boost

#endif // BOOST_VARIANT_DETAIL_APPLY_VISITOR_UNARY_HPP