boost/flyweight/key_value.hpp

   1 /* Copyright 2006-2008 Joaquin M Lopez Munoz.
   2  * Distributed under the Boost Software License, Version 1.0.
   3  * (See accompanying file LICENSE_1_0.txt or copy at
   4  * http://www.boost.org/LICENSE_1_0.txt)
   5  *
   6  * See http://www.boost.org/libs/flyweight for library home page.
   7  */
   8
   9 #ifndef BOOST_FLYWEIGHT_KEY_VALUE_HPP
  10 #define BOOST_FLYWEIGHT_KEY_VALUE_HPP
  11
  12 #if defined(_MSC_VER)&&(_MSC_VER>=1200)
  13 #pragma once
  14 #endif
  15
  16 #include <boost/flyweight/detail/value_tag.hpp>
  17 #include <boost/flyweight/key_value_fwd.hpp>
  18 #include <boost/mpl/assert.hpp>
  19 #include <boost/preprocessor/repetition/enum_params.hpp>
  20 #include <boost/type_traits/aligned_storage.hpp>
  21 #include <boost/type_traits/alignment_of.hpp>
  22 #include <boost/type_traits/is_same.hpp>
  23 #include <new>
  24
  25 /* key-value policy: flywewight lookup is based on Key, which also serves
  26  * to construct Value only when needed (new factory entry). key_value is
  27  * used to avoid the construction of temporary values when such construction
  28  * is expensive.
  29  * Optionally, KeyFromValue extracts the key from a value, which
  30  * is needed in expressions like this:
  31  *
  32  *  typedef flyweight<key_value<Key,Value> > fw_t;
  33  *  fw_t  fw;
  34  *  Value v;
  35  *  fw=v; // no key explicitly given
  36  *
  37  * If no KeyFromValue is provided, this latter expression fails to compile.
  38  */
  39
  40 namespace boost{
  41
  42 namespace flyweights{
  43
  44 namespace detail{
  45
  46 template<typename Key,typename Value,typename KeyFromValue>
  47 struct optimized_key_value:value_marker
  48 {
  49   typedef Key   key_type;
  50   typedef Value value_type;
  51
  52   class rep_type
  53   {
  54   public:
  55     /* template ctors */
  56
  57 #define BOOST_FLYWEIGHT_PERFECT_FWD_NAME explicit rep_type
  58 #define BOOST_FLYWEIGHT_PERFECT_FWD_BODY(n)          \
  59   :value_ptr(0)                                      \
  60 {                                                    \
  61   new(spc_ptr())key_type(BOOST_PP_ENUM_PARAMS(n,t)); \
  62 }
  63 #include <boost/flyweight/detail/perfect_fwd.hpp>
  64
  65     rep_type(const value_type& x):value_ptr(&x){}
  66
  67     rep_type(const rep_type& x):value_ptr(x.value_ptr)
  68     {
  69       if(!x.value_ptr)new(key_ptr())key_type(*x.key_ptr());
  70     }
  71
  72     ~rep_type()
  73     {
  74       if(!value_ptr)       key_ptr()->~key_type();
  75       else if(value_cted())value_ptr->~value_type();
  76     }
  77
  78     operator const key_type&()const
  79     {
  80       if(value_ptr)return key_from_value(*value_ptr);
  81       else         return *key_ptr();
  82     }
  83
  84     operator const value_type&()const
  85     {
  86       /* This is always called after construct_value() or copy_value(),
  87        * so we access spc directly rather than through value_ptr to
  88        * save us an indirection.
  89        */
  90
  91       return *static_cast<value_type*>(spc_ptr());
  92     }
  93
  94   private:
  95     friend struct optimized_key_value;
  96
  97     void* spc_ptr()const{return static_cast<void*>(&spc);}
  98     bool  value_cted()const{return value_ptr==spc_ptr();}
  99
 100     key_type* key_ptr()const
 101     {
 102       return static_cast<key_type*>(static_cast<void*>(&spc));
 103     }
 104
 105     static const key_type& key_from_value(const value_type& x)
 106     {
 107       KeyFromValue k;
 108       return k(x);
 109     }
 110
 111     void construct_value()const
 112     {
 113       if(!value_cted()){
 114         /* value_ptr must be ==0, oherwise copy_value would have been called */
 115
 116         key_type k(*key_ptr());
 117         key_ptr()->~key_type();
 118         value_ptr= /* guarantees key won't be re-dted at ~rep_type if the */
 119           static_cast<value_type*>(spc_ptr())+1; /* next statement throws */
 120         value_ptr=new(spc_ptr())value_type(k);
 121       }
 122     }
 123
 124     void copy_value()const
 125     {
 126       if(!value_cted())value_ptr=new(spc_ptr())value_type(*value_ptr);
 127     }
 128
 129     mutable typename boost::aligned_storage<
 130       (sizeof(key_type)>sizeof(value_type))?
 131         sizeof(key_type):sizeof(value_type),
 132       (boost::alignment_of<key_type>::value >
 133        boost::alignment_of<value_type>::value)?
 134         boost::alignment_of<key_type>::value:
 135         boost::alignment_of<value_type>::value
 136     >::type                                    spc;
 137     mutable const value_type*                  value_ptr;
 138   };
 139
 140   static void construct_value(const rep_type& r)
 141   {
 142     r.construct_value();
 143   }
 144
 145   static void copy_value(const rep_type& r)
 146   {
 147     r.copy_value();
 148   }
 149 };
 150
 151 template<typename Key,typename Value>
 152 struct regular_key_value:value_marker
 153 {
 154   typedef Key   key_type;
 155   typedef Value value_type;
 156
 157   class rep_type
 158   {
 159   public:
 160     /* template ctors */
 161
 162 #define BOOST_FLYWEIGHT_PERFECT_FWD_NAME explicit rep_type
 163 #define BOOST_FLYWEIGHT_PERFECT_FWD_BODY(n) \
 164   :key(BOOST_PP_ENUM_PARAMS(n,t)),value_ptr(0){}
 165 #include <boost/flyweight/detail/perfect_fwd.hpp>
 166
 167     rep_type(const value_type& x):key(no_key_from_value_failure()){}
 168
 169     rep_type(const rep_type& x):key(x.key),value_ptr(0){}
 170
 171     ~rep_type()
 172     {
 173       if(value_ptr)value_ptr->~value_type();
 174     }
 175
 176     operator const key_type&()const{return key;}
 177
 178     operator const value_type&()const
 179     {
 180       /* This is always called after construct_value(),so we access spc
 181        * directly rather than through value_ptr to save us an indirection.
 182        */
 183
 184       return *static_cast<value_type*>(spc_ptr());
 185     }
 186
 187   private:
 188     friend struct regular_key_value;
 189
 190     void* spc_ptr()const{return static_cast<void*>(&spc);}
 191
 192     struct no_key_from_value_failure
 193     {
 194       BOOST_MPL_ASSERT_MSG(
 195         false,
 196         NO_KEY_FROM_VALUE_CONVERSION_PROVIDED,
 197         (key_type,value_type));
 198
 199       operator const key_type&()const;
 200     };
 201
 202     void construct_value()const
 203     {
 204       if(!value_ptr)value_ptr=new(spc_ptr())value_type(key);
 205     }
 206
 207     key_type                                 key;
 208     mutable typename boost::aligned_storage<
 209       sizeof(value_type),
 210       boost::alignment_of<value_type>::value
 211     >::type                                  spc;
 212     mutable const value_type*                value_ptr;
 213   };
 214
 215   static void construct_value(const rep_type& r)
 216   {
 217     r.construct_value();
 218   }
 219
 220   static void copy_value(const rep_type&){}
 221 };
 222
 223 } /* namespace flyweights::detail */
 224
 225 template<typename Key,typename Value,typename KeyFromValue>
 226 struct key_value:
 227   mpl::if_<
 228     is_same<KeyFromValue,no_key_from_value>,
 229     detail::regular_key_value<Key,Value>,
 230     detail::optimized_key_value<Key,Value,KeyFromValue>
 231   >::type
 232 {};
 233
 234 } /* namespace flyweights */
 235
 236 } /* namespace boost */
 237
 238 #endif