ceph/src/boost/libs/type_erasure/include/boost/type_erasure/relaxed.hpp

   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  * - copy assignment of @ref any uses the copy 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