williamr@2: //-----------------------------------------------------------------------------
williamr@2: // boost variant/recursive_wrapper_fwd.hpp header file
williamr@2: // See http://www.boost.org for updates, documentation, and revision history.
williamr@2: //-----------------------------------------------------------------------------
williamr@2: //
williamr@2: // Copyright (c) 2002
williamr@2: // Eric Friedman, Itay Maman
williamr@2: //
williamr@2: // Portions Copyright (C) 2002 David Abrahams
williamr@2: //
williamr@2: // Distributed under the Boost Software License, Version 1.0. (See
williamr@2: // accompanying file LICENSE_1_0.txt or copy at
williamr@2: // http://www.boost.org/LICENSE_1_0.txt)
williamr@2: 
williamr@2: #ifndef BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
williamr@2: #define BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
williamr@2: 
williamr@2: #include "boost/mpl/aux_/config/ctps.hpp"
williamr@2: #if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
williamr@2: #   include "boost/mpl/eval_if.hpp"
williamr@2: #   include "boost/mpl/bool.hpp"
williamr@2: #   include "boost/mpl/identity.hpp"
williamr@2: #   include "boost/type.hpp"
williamr@2: #endif
williamr@2: 
williamr@2: #include "boost/mpl/aux_/lambda_support.hpp"
williamr@2: 
williamr@2: // should be the last #include
williamr@2: #include "boost/type_traits/detail/bool_trait_def.hpp"
williamr@2: 
williamr@2: namespace boost {
williamr@2: 
williamr@2: //////////////////////////////////////////////////////////////////////////
williamr@2: // class template recursive_wrapper
williamr@2: //
williamr@2: // Enables recursive types in templates by breaking cyclic dependencies.
williamr@2: //
williamr@2: // For example:
williamr@2: //
williamr@2: //   class my;
williamr@2: //
williamr@2: //   typedef variant< int, recursive_wrapper<my> > var;
williamr@2: //
williamr@2: //   class my {
williamr@2: //     var var_;
williamr@2: //     ...
williamr@2: //   };
williamr@2: //
williamr@2: template <typename T> class recursive_wrapper;
williamr@2: 
williamr@2: ///////////////////////////////////////////////////////////////////////////////
williamr@2: // metafunction is_recursive_wrapper (modeled on code by David Abrahams)
williamr@2: //
williamr@2: // True iff specified type matches recursive_wrapper<T>.
williamr@2: //
williamr@2: 
williamr@2: namespace detail {
williamr@2: 
williamr@2: #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
williamr@2: 
williamr@2: template <typename T>
williamr@2: struct is_recursive_wrapper_impl
williamr@2:     : mpl::false_
williamr@2: {
williamr@2: };
williamr@2: 
williamr@2: template <typename T>
williamr@2: struct is_recursive_wrapper_impl< recursive_wrapper<T> >
williamr@2:     : mpl::true_
williamr@2: {
williamr@2: };
williamr@2: 
williamr@2: #else // defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
williamr@2: 
williamr@2: typedef char (&yes_recursive_wrapper_t)[1];
williamr@2: typedef char (&no_recursive_wrapper_t)[2];
williamr@2: 
williamr@2: no_recursive_wrapper_t is_recursive_wrapper_test(...);
williamr@2: 
williamr@2: template<typename T>
williamr@2: yes_recursive_wrapper_t is_recursive_wrapper_test(
williamr@2:       type< ::boost::recursive_wrapper<T> >
williamr@2:     );
williamr@2: 
williamr@2: template<typename T>
williamr@2: struct is_recursive_wrapper_impl
williamr@2: {
williamr@2:     BOOST_STATIC_CONSTANT(bool, value = (
williamr@2:           sizeof(is_recursive_wrapper_test(type<T>()))
williamr@2:           == sizeof(yes_recursive_wrapper_t)
williamr@2:         ));
williamr@2: };
williamr@2: 
williamr@2: #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION workaround
williamr@2: 
williamr@2: } // namespace detail
williamr@2: 
williamr@2: BOOST_TT_AUX_BOOL_TRAIT_DEF1(
williamr@2:       is_recursive_wrapper
williamr@2:     , T
williamr@2:     , (::boost::detail::is_recursive_wrapper_impl<T>::value)
williamr@2:     )
williamr@2: 
williamr@2: ///////////////////////////////////////////////////////////////////////////////
williamr@2: // metafunction unwrap_recursive
williamr@2: //
williamr@2: // If specified type T matches recursive_wrapper<U>, then U; else T.
williamr@2: //
williamr@2: 
williamr@2: #if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
williamr@2: 
williamr@2: template <typename T>
williamr@2: struct unwrap_recursive
williamr@2: {
williamr@2:     typedef T type;
williamr@2: 
williamr@2:     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T))
williamr@2: };
williamr@2: 
williamr@2: template <typename T>
williamr@2: struct unwrap_recursive< recursive_wrapper<T> >
williamr@2: {
williamr@2:     typedef T type;
williamr@2: 
williamr@2:     BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(1,unwrap_recursive,(T))
williamr@2: };
williamr@2: 
williamr@2: #else // defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
williamr@2: 
williamr@2: template <typename T>
williamr@2: struct unwrap_recursive
williamr@2:     : mpl::eval_if<
williamr@2:           is_recursive_wrapper<T>
williamr@2:         , T
williamr@2:         , mpl::identity< T >
williamr@2:         >
williamr@2: {
williamr@2:     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T))
williamr@2: };
williamr@2: 
williamr@2: #endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION workaround
williamr@2: 
williamr@2: } // namespace boost
williamr@2: 
williamr@2: #include "boost/type_traits/detail/bool_trait_undef.hpp"
williamr@2: 
williamr@2: #endif // BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP