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- // 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
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