boost/type_erasure/param.hpp
// Boost.TypeErasure library // // Copyright 2011 Steven Watanabe // // 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) // // $Id$ #ifndef BOOST_TYPE_ERASURE_PARAM_HPP_INCLUDED #define BOOST_TYPE_ERASURE_PARAM_HPP_INCLUDED #include <boost/config.hpp> #include <boost/utility/enable_if.hpp> #include <boost/type_traits/is_same.hpp> #include <boost/type_traits/add_const.hpp> #include <boost/type_traits/remove_cv.hpp> #include <boost/type_traits/remove_reference.hpp> #include <boost/mpl/bool.hpp> #include <boost/mpl/if.hpp> #include <boost/type_erasure/detail/access.hpp> #include <boost/type_erasure/detail/storage.hpp> #include <boost/type_erasure/is_placeholder.hpp> #include <boost/type_erasure/concept_of.hpp> namespace boost { namespace type_erasure { #ifndef BOOST_TYPE_ERASURE_DOXYGEN template<class Concept, class T> class any; template<class Concept> class binding; #endif namespace detail { struct access; } namespace detail { template<class From, class To> struct placeholder_conversion : boost::mpl::false_ {}; template<class T> struct placeholder_conversion<T, T> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<T, T&> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<T, const T&> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<const T, T> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<const T, const T&> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<T&, T> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<T&, T&> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<T&, const T&> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<const T&, T> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<const T&, const T&> : boost::mpl::true_ {}; #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES template<class T> struct placeholder_conversion<T&&, T> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<T&&, const T&> : boost::mpl::true_ {}; template<class T> struct placeholder_conversion<T&&, T&&> : boost::mpl::true_ {}; #endif } /** * \brief A wrapper to help with overload resolution for functions * operating on an @ref any. * * The template arguments are interpreted in * the same way as @ref any. * * A parameter of type @ref param can be initialized * with an @ref any that has the same @c Concept * and base placeholder when there exists a corresponding * standard conversion for the placeholder. * A conversion sequence from @ref any "any<C, P>" to @ref param "param<C, P1>" is * a better conversion sequence than @ref any "any<C, P>" to @ref param "param<C, P2>" * iff the corresponding placeholder standard conversion * sequence from P to P1 is a better conversion sequence than * P to P2. * * \note Overloading based on cv-qualifiers and rvalue-ness is * only supported in C++11. In C++03, all conversion sequences * from @ref any to @ref param have the same rank. * * Example: * * \code * void f(param<C, _a&>); * void f(param<C, const _a&>); * void g(param<C, const _a&>); * void g(param<C, _a&&>); * * any<C, _a> a; * f(any<C, _a>()); // calls void f(param<C, const _a&>); * f(a); // calls void f(param<C, _a&>); (ambiguous in C++03) * g(any<C, _a>()); // calls void g(param<C, _a&&>); (ambiguous in C++03) * g(a); // calls void g(param<C, const _a&>); * \endcode * */ template<class Concept, class T> class param { public: friend struct boost::type_erasure::detail::access; /** INTERNAL ONLY */ typedef void _boost_type_erasure_is_any; /** INTERNAL ONLY */ typedef param _boost_type_erasure_derived_type; template<class U> param(any<Concept, U>& a #ifndef BOOST_TYPE_ERASURE_DOXYGEN , typename boost::enable_if< ::boost::type_erasure::detail::placeholder_conversion<U, T> >::type* = 0 #endif ) : _impl(a) {} template<class U> param(const any<Concept, U>& a #ifndef BOOST_TYPE_ERASURE_DOXYGEN , typename boost::enable_if< ::boost::type_erasure::detail::placeholder_conversion< typename ::boost::add_const<U>::type, T > >::type* = 0 #endif ) : _impl(a) {} #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES template<class U> param(any<Concept, U>&& a #ifndef BOOST_TYPE_ERASURE_DOXYGEN , typename boost::enable_if< ::boost::type_erasure::detail::placeholder_conversion< U&&, T > >::type* = 0 #endif ) : _impl(std::move(a)) {} #endif /** INTERNAL ONLY */ param(const ::boost::type_erasure::detail::storage& data, const ::boost::type_erasure::binding<Concept>& table) : _impl(data, table) {} /** Returns the stored @ref any. */ any<Concept, T> get() const { return _impl; } private: any<Concept, T> _impl; }; #if !defined(BOOST_NO_CXX11_REF_QUALIFIERS) && !defined(BOOST_TYPE_ERASURE_DOXYGEN) template<class Concept, class T> class param<Concept, const T&> { public: friend struct boost::type_erasure::detail::access; /** INTERNAL ONLY */ typedef void _boost_type_erasure_is_any; /** INTERNAL ONLY */ typedef param _boost_type_erasure_derived_type; param(const ::boost::type_erasure::detail::storage& data, const ::boost::type_erasure::binding<Concept>& table) : _impl(data, table) {} template<class U> param(U& u, typename boost::enable_if< ::boost::is_same<U, const any<Concept, T> > >::type* = 0) : _impl(u) {} any<Concept, const T&> get() const { return _impl; } protected: struct _impl_t { _impl_t(const ::boost::type_erasure::detail::storage& data_, const ::boost::type_erasure::binding<Concept>& table_) : table(table_), data(data_) {} _impl_t(const any<Concept, T>& u) : table(::boost::type_erasure::detail::access::table(u)), data(::boost::type_erasure::detail::access::data(u)) {} // It's safe to capture the table by reference, because // the user's argument should out-live us. storage is // just a void*, so we don't need to add indirection. const ::boost::type_erasure::binding<Concept>& table; ::boost::type_erasure::detail::storage data; } _impl; }; template<class Concept, class T> class param<Concept, T&> : public param<Concept, const T&> { public: friend struct boost::type_erasure::detail::access; /** INTERNAL ONLY */ typedef void _boost_type_erasure_is_any; /** INTERNAL ONLY */ typedef param _boost_type_erasure_derived_type; param(const ::boost::type_erasure::detail::storage& data, const ::boost::type_erasure::binding<Concept>& table) : param<Concept, const T&>(data, table) {} any<Concept, T&> get() const { return any<Concept, T&>( ::boost::type_erasure::detail::access::data(this->_impl), ::boost::type_erasure::detail::access::table(this->_impl)); } }; #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES template<class Concept, class T> class param<Concept, T&&> : public param<Concept, const T&> { public: friend struct boost::type_erasure::detail::access; /** INTERNAL ONLY */ typedef void _boost_type_erasure_is_any; /** INTERNAL ONLY */ typedef param _boost_type_erasure_derived_type; param(const ::boost::type_erasure::detail::storage& data, const ::boost::type_erasure::binding<Concept>& table) : param<Concept, const T&>(data, table) {} any<Concept, T&&> get() const { return any<Concept, T&&>( ::boost::type_erasure::detail::access::data(this->_impl), ::boost::type_erasure::detail::access::table(this->_impl)); } }; #endif #endif /** * \brief Metafunction that creates a @ref param. * * If @c T is a (cv/reference qualified) placeholder, * returns @ref param<@ref concept_of "concept_of<Any>::type", T>, * otherwise, returns T. This metafunction is intended * to be used for function arguments in specializations of * @ref concept_interface. * * \see derived, rebind_any */ template<class Any, class T> struct as_param { #ifdef BOOST_TYPE_ERASURE_DOXYGEN typedef detail::unspecified type; #else typedef typename ::boost::mpl::if_< ::boost::type_erasure::is_placeholder< typename ::boost::remove_cv< typename ::boost::remove_reference<T>::type>::type>, param<typename ::boost::type_erasure::concept_of<Any>::type, T>, T >::type type; #endif }; #ifndef BOOST_NO_CXX11_TEMPLATE_ALIASES template<class Any, class T> using as_param_t = typename ::boost::type_erasure::as_param<Any, T>::type; #endif } } #endif