ceph/src/boost/libs/type_erasure/include/boost/type_erasure/param.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_PARAM_HPP_INCLUDED
  12 #define BOOST_TYPE_ERASURE_PARAM_HPP_INCLUDED
  13
  14 #include <boost/config.hpp>
  15 #include <boost/utility/enable_if.hpp>
  16 #include <boost/type_traits/is_same.hpp>
  17 #include <boost/type_traits/add_const.hpp>
  18 #include <boost/type_traits/remove_cv.hpp>
  19 #include <boost/type_traits/remove_reference.hpp>
  20 #include <boost/mpl/bool.hpp>
  21 #include <boost/mpl/if.hpp>
  22 #include <boost/type_erasure/detail/access.hpp>
  23 #include <boost/type_erasure/detail/storage.hpp>
  24 #include <boost/type_erasure/is_placeholder.hpp>
  25 #include <boost/type_erasure/concept_of.hpp>
  26
  27 namespace boost {
  28 namespace type_erasure {
  29
  30 template<class Concept, class T>
  31 class any;
  32
  33 template<class Concept>
  34 class binding;
  35
  36 namespace detail {
  37
  38 struct access;
  39
  40 }
  41
  42 namespace detail {
  43
  44 template<class From, class To>
  45 struct placeholder_conversion : boost::mpl::false_ {};
  46 template<class T>
  47 struct placeholder_conversion<T, T> : boost::mpl::true_ {};
  48 template<class T>
  49 struct placeholder_conversion<T, T&> : boost::mpl::true_ {};
  50 template<class T>
  51 struct placeholder_conversion<T, const T&> : boost::mpl::true_ {};
  52 template<class T>
  53 struct placeholder_conversion<const T, T> : boost::mpl::true_ {};
  54 template<class T>
  55 struct placeholder_conversion<const T, const T&> : boost::mpl::true_ {};
  56 template<class T>
  57 struct placeholder_conversion<T&, T> : boost::mpl::true_ {};
  58 template<class T>
  59 struct placeholder_conversion<T&, T&> : boost::mpl::true_ {};
  60 template<class T>
  61 struct placeholder_conversion<T&, const T&> : boost::mpl::true_ {};
  62 template<class T>
  63 struct placeholder_conversion<const T&, T> : boost::mpl::true_ {};
  64 template<class T>
  65 struct placeholder_conversion<const T&, const T&> : boost::mpl::true_ {};
  66
  67 #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
  68 template<class T>
  69 struct placeholder_conversion<T&&, T> : boost::mpl::true_ {};
  70 template<class T>
  71 struct placeholder_conversion<T&&, const T&> : boost::mpl::true_ {};
  72 template<class T>
  73 struct placeholder_conversion<T&&, T&&> : boost::mpl::true_ {};
  74 #endif
  75
  76 }
  77
  78 #ifdef __clang__
  79 #if !__has_feature(cxx_reference_qualified_functions)
  80 /** INTERNAL ONLY */
  81 #define BOOST_NO_FUNCTION_REFERENCE_QUALIFIERS
  82 #endif
  83 #else
  84 /** INTERNAL ONLY */
  85 #define BOOST_NO_FUNCTION_REFERENCE_QUALIFIERS
  86 #endif
  87
  88 /**
  89  * \brief A wrapper to help with overload resolution for functions
  90  * operating on an @ref any.
  91  *
  92  * The template arguments are interpreted in
  93  * the same way as @ref any.
  94  *
  95  * A parameter of type @ref param can be initialized
  96  * with an @ref any that has the same @c Concept
  97  * and base placeholder when there exists a corresponding
  98  * standard conversion for the placeholder.
  99  * A conversion sequence from @ref any<C, P> to @ref param<C, P1> is
 100  * a better conversion sequence than @ref any<C, P> to @ref param<C, P2>
 101  * iff the corresponding placeholder standard conversion
 102  * sequence from P to P1 is a better conversion sequence than
 103  * P to P2.
 104  *
 105  * \note Overloading based on cv-qualifiers and rvalue-ness is
 106  * only supported in C++11.  In C++03, all conversion sequences
 107  * from @ref any to @ref param have the same rank.
 108  *
 109  * Example:
 110  *
 111  * \code
 112  * void f(param<C, _a&>);
 113  * void f(param<C, const _a&>);
 114  * void g(param<C, const _a&>);
 115  * void g(param<C, _a&&>);
 116  *
 117  * any<C, _a> a;
 118  * f(any<C, _a>()); // calls void f(param<C, const _a&>);
 119  * f(a);            // calls void f(param<C, _a&>); (ambiguous in C++03)
 120  * g(any<C, _a>()); // calls void g(param<C, _a&&>); (ambiguous in C++03)
 121  * g(a);            // calls void g(param<C, const _a&>);
 122  * \endcode
 123  *
 124  */
 125 template<class Concept, class T>
 126 class param {
 127 public:
 128
 129     friend struct boost::type_erasure::detail::access;
 130
 131     /** INTERNAL ONLY */
 132     typedef void _boost_type_erasure_is_any;
 133     /** INTERNAL ONLY */
 134     typedef param _boost_type_erasure_derived_type;
 135
 136     template<class U>
 137     param(any<Concept, U>& a
 138 #ifndef BOOST_TYPE_ERASURE_DOXYGEN
 139         , typename boost::enable_if<
 140             ::boost::type_erasure::detail::placeholder_conversion<U, T>
 141         >::type* = 0
 142 #endif
 143         )
 144       : _impl(a)
 145     {}
 146     template<class U>
 147     param(const any<Concept, U>& a
 148 #ifndef BOOST_TYPE_ERASURE_DOXYGEN
 149         , typename boost::enable_if<
 150             ::boost::type_erasure::detail::placeholder_conversion<
 151                 typename ::boost::add_const<U>::type,
 152                 T
 153             >
 154         >::type* = 0
 155 #endif
 156         )
 157       : _impl(a)
 158     {}
 159 #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
 160     template<class U>
 161     param(any<Concept, U>&& a
 162 #ifndef BOOST_TYPE_ERASURE_DOXYGEN
 163         , typename boost::enable_if<
 164             ::boost::type_erasure::detail::placeholder_conversion<
 165                 U&&,
 166                 T
 167             >
 168         >::type* = 0
 169 #endif
 170         )
 171       : _impl(std::move(a))
 172     {}
 173 #endif
 174
 175     /** Returns the stored @ref any. */
 176     any<Concept, T> get() const { return _impl; }
 177 private:
 178     any<Concept, T> _impl;
 179 };
 180
 181 #ifndef BOOST_NO_FUNCTION_REFERENCE_QUALIFIERS
 182
 183 template<class Concept, class T>
 184 class param<Concept, const T&> {
 185 public:
 186
 187     friend struct boost::type_erasure::detail::access;
 188
 189     /** INTERNAL ONLY */
 190     typedef void _boost_type_erasure_is_any;
 191     /** INTERNAL ONLY */
 192     typedef param _boost_type_erasure_derived_type;
 193
 194     param(const ::boost::type_erasure::detail::storage& data,
 195           const ::boost::type_erasure::binding<Concept>& table)
 196       : _impl(data, table)
 197     {}
 198     template<class U>
 199     param(U& u, typename boost::enable_if< ::boost::is_same<U, const any<Concept, T> > >::type* = 0) : _impl(u) {}
 200     any<Concept, const T&> get() const { return _impl; }
 201 protected:
 202     any<Concept, const T&> _impl;
 203 };
 204
 205 template<class Concept, class T>
 206 class param<Concept, T&> : public param<Concept, const T&> {
 207 public:
 208
 209     friend struct boost::type_erasure::detail::access;
 210
 211     /** INTERNAL ONLY */
 212     typedef void _boost_type_erasure_is_any;
 213     /** INTERNAL ONLY */
 214     typedef param _boost_type_erasure_derived_type;
 215
 216     param(const ::boost::type_erasure::detail::storage& data,
 217           const ::boost::type_erasure::binding<Concept>& table)
 218       : param<Concept, const T&>(data, table)
 219     {}
 220     any<Concept, T&> get() const
 221     {
 222         return any<Concept, T&>(
 223             ::boost::type_erasure::detail::access::data(this->_impl),
 224             ::boost::type_erasure::detail::access::table(this->_impl));
 225     }
 226 };
 227
 228 #ifndef BOOST_NO_CXX11_RVALUE_REFERENCES
 229
 230 template<class Concept, class T>
 231 class param<Concept, T&&> : public param<Concept, const T&> {
 232 public:
 233
 234     friend struct boost::type_erasure::detail::access;
 235
 236     /** INTERNAL ONLY */
 237     typedef void _boost_type_erasure_is_any;
 238     /** INTERNAL ONLY */
 239     typedef param _boost_type_erasure_derived_type;
 240
 241     param(const ::boost::type_erasure::detail::storage& data,
 242           const ::boost::type_erasure::binding<Concept>& table)
 243       : param<Concept, const T&>(data, table)
 244     {}
 245     any<Concept, T&&> get() const
 246     {
 247         return any<Concept, T&&>(
 248             ::boost::type_erasure::detail::access::data(this->_impl),
 249             ::boost::type_erasure::detail::access::table(this->_impl));
 250     }
 251 };
 252
 253 #endif
 254
 255 #endif
 256
 257 /**
 258  * \brief Metafunction that creates a @ref param.
 259  *
 260  * If @c T is a (cv/reference qualifed) placeholder,
 261  * returns @ref param<@ref concept_of "concept_of<Any>::type", T>,
 262  * otherwise, returns T.  This metafunction is intended
 263  * to be used for function arguments in specializations of
 264  * @ref concept_interface.
 265  *
 266  * \see derived, rebind_any
 267  */
 268 template<class Any, class T>
 269 struct as_param {
 270 #ifdef BOOST_TYPE_ERASURE_DOXYGEN
 271     typedef detail::unspecified type;
 272 #else
 273     typedef typename ::boost::mpl::if_<
 274         ::boost::type_erasure::is_placeholder<
 275             typename ::boost::remove_cv<
 276                 typename ::boost::remove_reference<T>::type>::type>,
 277         param<typename ::boost::type_erasure::concept_of<Any>::type, T>,
 278         T
 279     >::type type;
 280 #endif
 281 };
 282
 283 }
 284 }
 285
 286 #endif