//-----------------------------------------------------------------------------

 // boost variant/static_visitor.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_STATIC_VISITOR_HPP

 #define BOOST_VARIANT_STATIC_VISITOR_HPP

 #include "boost/config.hpp"

 #include "boost/detail/workaround.hpp"

 #include "boost/mpl/if.hpp"

 #include "boost/type_traits/is_base_and_derived.hpp"

 #if BOOST_WORKAROUND(BOOST_MSVC, < 1300)

 #   include "boost/type_traits/is_same.hpp"

 #endif

 // should be the last #include

 #include "boost/type_traits/detail/bool_trait_def.hpp"

 namespace boost {

 //////////////////////////////////////////////////////////////////////////

 // class template static_visitor

 //

 // An empty base class that typedefs the return type of a deriving static

 // visitor. The class is analogous to std::unary_function in this role.

 //

 namespace detail {

     struct is_static_visitor_tag { };

     typedef void static_visitor_default_return;

 } // namespace detail

 template <typename R = ::boost::detail::static_visitor_default_return>

 class static_visitor

     : public detail::is_static_visitor_tag

 {

 public: // typedefs

     typedef R result_type;

 protected: // for use as base class only

     static_visitor() { }

     ~static_visitor() { }

 };

 //////////////////////////////////////////////////////////////////////////

 // metafunction is_static_visitor

 //

 // Value metafunction indicates whether the specified type derives from

 // static_visitor<...>.

 //

 // NOTE #1: This metafunction does NOT check whether the specified type

 //  fulfills the requirements of the StaticVisitor concept.

 //

 // NOTE #2: This template never needs to be specialized!

 //

 namespace detail {

 template <typename T>

 struct is_static_visitor_impl

 {

     BOOST_STATIC_CONSTANT(bool, value = 

         (::boost::is_base_and_derived< 

             detail::is_static_visitor_tag,

             T

         >::value));

 };

 } // namespace detail

 BOOST_TT_AUX_BOOL_TRAIT_DEF1(

       is_static_visitor

     , T

     , (::boost::detail::is_static_visitor_impl<T>::value)

     )

 } // namespace boost

 #include "boost/type_traits/detail/bool_trait_undef.hpp"

 #endif // BOOST_VARIANT_STATIC_VISITOR_HPP