ceph/src/boost/libs/variant/include/boost/variant/recursive_wrapper_fwd.hpp

   1 //-----------------------------------------------------------------------------
   2 // boost variant/recursive_wrapper_fwd.hpp header file
   3 // See http://www.boost.org for updates, documentation, and revision history.
   4 //-----------------------------------------------------------------------------
   5 //
   6 // Copyright (c) 2002 Eric Friedman, Itay Maman
   7 // Copyright (c) 2016 Antony Polukhin
   8 //
   9 // Portions Copyright (C) 2002 David Abrahams
  10 //
  11 // Distributed under the Boost Software License, Version 1.0. (See
  12 // accompanying file LICENSE_1_0.txt or copy at
  13 // http://www.boost.org/LICENSE_1_0.txt)
  14
  15 #ifndef BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
  16 #define BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP
  17
  18 #include <boost/mpl/bool.hpp>
  19 #include <boost/mpl/aux_/config/ctps.hpp>
  20 #include <boost/mpl/aux_/lambda_support.hpp>
  21 #include <boost/type_traits/integral_constant.hpp>
  22 #include <boost/type_traits/is_constructible.hpp>
  23
  24 namespace boost {
  25
  26 //////////////////////////////////////////////////////////////////////////
  27 // class template recursive_wrapper
  28 //
  29 // Enables recursive types in templates by breaking cyclic dependencies.
  30 //
  31 // For example:
  32 //
  33 //   class my;
  34 //
  35 //   typedef variant< int, recursive_wrapper<my> > var;
  36 //
  37 //   class my {
  38 //     var var_;
  39 //     ...
  40 //   };
  41 //
  42 template <typename T> class recursive_wrapper;
  43
  44
  45 ///////////////////////////////////////////////////////////////////////////////
  46 // metafunction is_constructible partial specializations.
  47 //
  48 // recursive_wrapper<T> is constructible only from T and recursive_wrapper<T>.
  49 //
  50 template <class T>          struct is_constructible<recursive_wrapper<T>, T>                            : boost::true_type{};
  51 template <class T>          struct is_constructible<recursive_wrapper<T>, const T>                      : boost::true_type{};
  52 template <class T>          struct is_constructible<recursive_wrapper<T>, T&>                           : boost::true_type{};
  53 template <class T>          struct is_constructible<recursive_wrapper<T>, const T&>                     : boost::true_type{};
  54 template <class T>          struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T> >        : boost::true_type{};
  55 template <class T>          struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T> >  : boost::true_type{};
  56 template <class T>          struct is_constructible<recursive_wrapper<T>, recursive_wrapper<T>& >       : boost::true_type{};
  57 template <class T>          struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<T>& > : boost::true_type{};
  58
  59 template <class T, class U> struct is_constructible<recursive_wrapper<T>, U >                           : boost::false_type{};
  60 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U >                     : boost::false_type{};
  61 template <class T, class U> struct is_constructible<recursive_wrapper<T>, U& >                          : boost::false_type{};
  62 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const U& >                    : boost::false_type{};
  63 template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U> >        : boost::false_type{};
  64 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U> >  : boost::false_type{};
  65 template <class T, class U> struct is_constructible<recursive_wrapper<T>, recursive_wrapper<U>& >       : boost::false_type{};
  66 template <class T, class U> struct is_constructible<recursive_wrapper<T>, const recursive_wrapper<U>& > : boost::false_type{};
  67
  68
  69 ///////////////////////////////////////////////////////////////////////////////
  70 // metafunction is_recursive_wrapper (modeled on code by David Abrahams)
  71 //
  72 // True if specified type matches recursive_wrapper<T>.
  73 //
  74
  75 namespace detail {
  76
  77
  78 template <typename T>
  79 struct is_recursive_wrapper_impl
  80     : mpl::false_
  81 {
  82 };
  83
  84 template <typename T>
  85 struct is_recursive_wrapper_impl< recursive_wrapper<T> >
  86     : mpl::true_
  87 {
  88 };
  89
  90
  91 } // namespace detail
  92
  93 template< typename T > struct is_recursive_wrapper
  94     : public ::boost::integral_constant<bool,(::boost::detail::is_recursive_wrapper_impl<T>::value)>
  95 {
  96 public:
  97     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_recursive_wrapper,(T))
  98 };
  99
 100 ///////////////////////////////////////////////////////////////////////////////
 101 // metafunction unwrap_recursive
 102 //
 103 // If specified type T matches recursive_wrapper<U>, then U; else T.
 104 //
 105
 106
 107 template <typename T>
 108 struct unwrap_recursive
 109 {
 110     typedef T type;
 111
 112     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,unwrap_recursive,(T))
 113 };
 114
 115 template <typename T>
 116 struct unwrap_recursive< recursive_wrapper<T> >
 117 {
 118     typedef T type;
 119
 120     BOOST_MPL_AUX_LAMBDA_SUPPORT_SPEC(1,unwrap_recursive,(T))
 121 };
 122
 123
 124 } // namespace boost
 125
 126 #endif // BOOST_VARIANT_RECURSIVE_WRAPPER_FWD_HPP