//----------------------------------------------------------------------------- // boost variant/recursive_wrapper_fwd.hpp header file // See http://www.boost.org for updates, documentation, and revision history. //----------------------------------------------------------------------------- // // Copyright (c) 2002 Eric Friedman, Itay Maman // Copyright (c) 2016 Antony Polukhin // // Portions Copyright (C) 2002 David Abrahams // // 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_RECURSIVE_WRAPPER_FWD_HPP #define BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP #include <boost/mpl/bool.hpp> #include <boost/mpl/aux_/config/ctps.hpp> #include <boost/mpl/aux_/lambda_support.hpp> #include <boost/type_traits/integral_constant.hpp> #include <boost/type_traits/is_constructible.hpp> namespace boost { ////////////////////////////////////////////////////////////////////////// // class template recursive_wrapper // // Enables recursive types in templates by breaking cyclic dependencies. // // For example: // // class my; // // typedef variant< int, recursive_wrapper<my> > var; // // class my { // var var_; // ... // }; // template <typename T> class recursive_wrapper; /////////////////////////////////////////////////////////////////////////////// // metafunction is_constructible partial specializations. // // recursive_wrapper<T> is constructible only from T and recursive_wrapper<T>. // template <class T> struct is_constructible<recursive_wrapper<T>, T> : boost::true_type{}; template <class T> struct is_constructible<recursive_wrapper<T>, const T> : boost::true_type{}; template <class T> struct is_constructible<recursive_wrapper<T>, T&> : boost::true_type{}; template <class T> struct is_constructible<recursive_wrapper<T>, const T&> : boost::true_type{}; template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T> > : boost::true_type{}; template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T> > : boost::true_type{}; template <class T> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T>& > : boost::true_type{}; template <class T> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T>& > : boost::true_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, U > : boost::false_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U > : boost::false_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, U& > : boost::false_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U& > : boost::false_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U> > : boost::false_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U> > : boost::false_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U>& > : boost::false_type{}; template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U>& > : boost::false_type{}; /////////////////////////////////////////////////////////////////////////////// // metafunction is_recursive_wrapper (modeled on code by David Abrahams) // // True if specified type matches recursive_wrapper<T>. // namespace detail { template <typename T> struct is_recursive_wrapper_impl : mpl::false_ { }; template <typename T> struct is_recursive_wrapper_impl< recursive_wrapper<T> > : mpl::true_ { }; } // namespace detail template< typename T > struct is_recursive_wrapper : public ::boost::integral_constant<bool,(::boost::detail::is_recursive_wrapper_impl<T>::value)> { public: BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_recursive_wrapper,(T)) }; /////////////////////////////////////////////////////////////////////////////// // metafunction unwrap_recursive // // If specified type T matches recursive_wrapper<U>, then U; else T. // template <typename T> struct unwrap_recursive { typedef T type; BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T)) }; template <typename T> struct unwrap_recursive< recursive_wrapper<T> > { typedef T type; BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(1,unwrap_recursive,(T)) }; } // namespace boost #endif // BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP