1 // Boost.TypeErasure library 2 // 3 // Copyright 2011 Steven Watanabe 4 // 5 // Distributed under the Boost Software License Version 1.0. (See 6 // accompanying file LICENSE_1_0.txt or copy at 7 // http://www.boost.org/LICENSE_1_0.txt) 8 // 9 // $Id$ 10 11 #ifndef BOOST_TYPE_ERASURE_RELAXED_HPP_INCLUDED 12 #define BOOST_TYPE_ERASURE_RELAXED_HPP_INCLUDED 13 14 #include <boost/mpl/vector.hpp> 15 #include <boost/mpl/bool.hpp> 16 #include <boost/mpl/is_sequence.hpp> 17 #include <boost/mpl/find_if.hpp> 18 #include <boost/mpl/not.hpp> 19 #include <boost/mpl/end.hpp> 20 #include <boost/type_traits/is_same.hpp> 21 22 namespace boost { 23 namespace type_erasure { 24 25 template<class T> 26 struct is_relaxed; 27 28 namespace detail { 29 30 template<class T> 31 struct is_relaxed_impl : 32 ::boost::mpl::not_< 33 typename ::boost::is_same< 34 typename ::boost::mpl::find_if< 35 T, 36 ::boost::type_erasure::is_relaxed< ::boost::mpl::_1> 37 >::type, 38 typename ::boost::mpl::end<T>::type 39 >::type 40 >::type 41 {}; 42 43 } 44 45 /** 46 * This special concept enables various useful default behavior that 47 * makes @ref any act like an ordinary object. By default @ref any 48 * forwards all operations to the underlying type, and provides only 49 * the operations that are specified in its @c Concept. 50 * 51 * In detail, @ref relaxed enables the following: 52 * - A raw value can be assigned to an @ref any. This will replace 53 * the value stored by the @ref any. (But note that if @ref assignable 54 * is present, it takes priority.) 55 * - assignment of @ref any uses the constructor if it can't 56 * use @ref assignable (either because @ref assignable is missing, 57 * or because the stored types do not match). 58 * - default construction of @ref any is allowed and creates a null any. 59 * - @ref equality_comparable "equality_comparable": If the types do not 60 * match, it will return false. 61 * - @ref less_than_comparable "less_than_comparable": If the types do not 62 * match, the ordering will be according to 63 * @c std::type_info::before. 64 * - if the arguments to any other function do not match, it will throw 65 * a @ref bad_function_call exception instead of having undefined 66 * behavior. 67 */ 68 struct relaxed : ::boost::mpl::vector0<> {}; 69 70 /** 71 * A metafunction indicating whether @c Concept 72 * includes @ref relaxed. 73 */ 74 template<class Concept> 75 struct is_relaxed : 76 ::boost::mpl::eval_if< ::boost::mpl::is_sequence<Concept>, 77 ::boost::type_erasure::detail::is_relaxed_impl<Concept>, 78 ::boost::mpl::false_ 79 >::type 80 {}; 81 82 /** INTERNAL ONLY */ 83 template<> 84 struct is_relaxed< ::boost::type_erasure::relaxed> : 85 ::boost::mpl::true_ 86 {}; 87 88 } 89 } 90 91 #endif 92