boost/any.hpp

   1 // See http://www.boost.org/libs/any for Documentation.
   2
   3 #ifndef BOOST_ANY_INCLUDED
   4 #define BOOST_ANY_INCLUDED
   5
   6 // what:  variant type boost::any
   7 // who:   contributed by Kevlin Henney,
   8 //        with features contributed and bugs found by
   9 //        Ed Brey, Mark Rodgers, Peter Dimov, and James Curran
  10 // when:  July 2001
  11 // where: tested with BCC 5.5, MSVC 6.0, and g++ 2.95
  12
  13 #include <algorithm>
  14 #include <typeinfo>
  15
  16 #include "boost/config.hpp"
  17 #include <boost/type_traits/remove_reference.hpp>
  18 #include <boost/type_traits/is_reference.hpp>
  19 #include <boost/throw_exception.hpp>
  20 #include <boost/static_assert.hpp>
  21
  22 namespace boost
  23 {
  24     class any
  25     {
  26     public: // structors
  27
  28         any()
  29           : content(0)
  30         {
  31         }
  32
  33         template<typename ValueType>
  34         any(const ValueType & value)
  35           : content(new holder<ValueType>(value))
  36         {
  37         }
  38
  39         any(const any & other)
  40           : content(other.content ? other.content->clone() : 0)
  41         {
  42         }
  43
  44         ~any()
  45         {
  46             delete content;
  47         }
  48
  49     public: // modifiers
  50
  51         any & swap(any & rhs)
  52         {
  53             std::swap(content, rhs.content);
  54             return *this;
  55         }
  56
  57         template<typename ValueType>
  58         any & operator=(const ValueType & rhs)
  59         {
  60             any(rhs).swap(*this);
  61             return *this;
  62         }
  63
  64         any & operator=(any rhs)
  65         {
  66             rhs.swap(*this);
  67             return *this;
  68         }
  69
  70     public: // queries
  71
  72         bool empty() const
  73         {
  74             return !content;
  75         }
  76
  77         const std::type_info & type() const
  78         {
  79             return content ? content->type() : typeid(void);
  80         }
  81
  82 #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
  83     private: // types
  84 #else
  85     public: // types (public so any_cast can be non-friend)
  86 #endif
  87
  88         class placeholder
  89         {
  90         public: // structors
  91
  92             virtual ~placeholder()
  93             {
  94             }
  95
  96         public: // queries
  97
  98             virtual const std::type_info & type() const = 0;
  99
 100             virtual placeholder * clone() const = 0;
 101
 102         };
 103
 104         template<typename ValueType>
 105         class holder : public placeholder
 106         {
 107         public: // structors
 108
 109             holder(const ValueType & value)
 110               : held(value)
 111             {
 112             }
 113
 114         public: // queries
 115
 116             virtual const std::type_info & type() const
 117             {
 118                 return typeid(ValueType);
 119             }
 120
 121             virtual placeholder * clone() const
 122             {
 123                 return new holder(held);
 124             }
 125
 126         public: // representation
 127
 128             ValueType held;
 129
 130         private: // intentionally left unimplemented
 131             holder & operator=(const holder &);
 132         };
 133
 134 #ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
 135
 136     private: // representation
 137
 138         template<typename ValueType>
 139         friend ValueType * any_cast(any *);
 140
 141         template<typename ValueType>
 142         friend ValueType * unsafe_any_cast(any *);
 143
 144 #else
 145
 146     public: // representation (public so any_cast can be non-friend)
 147
 148 #endif
 149
 150         placeholder * content;
 151
 152     };
 153
 154     class bad_any_cast : public std::bad_cast
 155     {
 156     public:
 157         virtual const char * what() const throw()
 158         {
 159             return "boost::bad_any_cast: "
 160                    "failed conversion using boost::any_cast";
 161         }
 162     };
 163
 164     template<typename ValueType>
 165     ValueType * any_cast(any * operand)
 166     {
 167         return operand && operand->type() == typeid(ValueType)
 168                     ? &static_cast<any::holder<ValueType> *>(operand->content)->held
 169                     : 0;
 170     }
 171
 172     template<typename ValueType>
 173     inline const ValueType * any_cast(const any * operand)
 174     {
 175         return any_cast<ValueType>(const_cast<any *>(operand));
 176     }
 177
 178     template<typename ValueType>
 179     ValueType any_cast(any & operand)
 180     {
 181         typedef BOOST_DEDUCED_TYPENAME remove_reference<ValueType>::type nonref;
 182
 183 #ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 184         // If 'nonref' is still reference type, it means the user has not
 185         // specialized 'remove_reference'.
 186
 187         // Please use BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION macro
 188         // to generate specialization of remove_reference for your class
 189         // See type traits library documentation for details
 190         BOOST_STATIC_ASSERT(!is_reference<nonref>::value);
 191 #endif
 192
 193         nonref * result = any_cast<nonref>(&operand);
 194         if(!result)
 195             boost::throw_exception(bad_any_cast());
 196         return *result;
 197     }
 198
 199     template<typename ValueType>
 200     inline ValueType any_cast(const any & operand)
 201     {
 202         typedef BOOST_DEDUCED_TYPENAME remove_reference<ValueType>::type nonref;
 203
 204 #ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
 205         // The comment in the above version of 'any_cast' explains when this
 206         // assert is fired and what to do.
 207         BOOST_STATIC_ASSERT(!is_reference<nonref>::value);
 208 #endif
 209
 210         return any_cast<const nonref &>(const_cast<any &>(operand));
 211     }
 212
 213     // Note: The "unsafe" versions of any_cast are not part of the
 214     // public interface and may be removed at any time. They are
 215     // required where we know what type is stored in the any and can't
 216     // use typeid() comparison, e.g., when our types may travel across
 217     // different shared libraries.
 218     template<typename ValueType>
 219     inline ValueType * unsafe_any_cast(any * operand)
 220     {
 221         return &static_cast<any::holder<ValueType> *>(operand->content)->held;
 222     }
 223
 224     template<typename ValueType>
 225     inline const ValueType * unsafe_any_cast(const any * operand)
 226     {
 227         return unsafe_any_cast<ValueType>(const_cast<any *>(operand));
 228     }
 229 }
 230
 231 // Copyright Kevlin Henney, 2000, 2001, 2002. All rights reserved.
 232 //
 233 // Distributed under the Boost Software License, Version 1.0. (See
 234 // accompanying file LICENSE_1_0.txt or copy at
 235 // http://www.boost.org/LICENSE_1_0.txt)
 236
 237 #endif