1 // (C) Copyright 2002-2008, Fernando Luis Cacciola Carballal.
2 //
3 // Distributed under the Boost Software License, Version 1.0. (See
4 // accompanying file LICENSE_1_0.txt or copy at
5 // http://www.boost.org/LICENSE_1_0.txt)
6 //
7 // 21 Ago 2002 (Created) Fernando Cacciola
8 // 24 Dec 2007 (Refactored and worked around various compiler bugs) Fernando Cacciola, Niels Dekker
9 // 23 May 2008 (Fixed operator= const issue, added initialized_value) Niels Dekker, Fernando Cacciola
10 // 21 Ago 2008 (Added swap) Niels Dekker, Fernando Cacciola
11 // 20 Feb 2009 (Fixed logical const-ness issues) Niels Dekker, Fernando Cacciola
12 // 03 Apr 2010 (Added initialized<T>, suggested by Jeffrey Hellrung, fixing #3472) Niels Dekker
13 // 30 May 2010 (Made memset call conditional, fixing #3869) Niels Dekker
14 //
15 #ifndef BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
16 #define BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
17
18 // Note: The implementation of boost::value_initialized had to deal with the
19 // fact that various compilers haven't fully implemented value-initialization.
20 // The constructor of boost::value_initialized<T> works around these compiler
21 // issues, by clearing the bytes of T, before constructing the T object it
22 // contains. More details on these issues are at libs/utility/value_init.htm
23
24 #include <boost/aligned_storage.hpp>
25 #include <boost/config.hpp> // For BOOST_NO_COMPLETE_VALUE_INITIALIZATION.
26 #include <boost/detail/workaround.hpp>
27 #include <boost/static_assert.hpp>
28 #include <boost/type_traits/cv_traits.hpp>
29 #include <boost/type_traits/alignment_of.hpp>
30 #include <boost/swap.hpp>
31 #include <cstring>
32 #include <new>
33
34 #ifdef BOOST_MSVC
35 #pragma warning(push)
36 #if _MSC_VER >= 1310
37 // It is safe to ignore the following warning from MSVC 7.1 or higher:
38 // "warning C4351: new behavior: elements of array will be default initialized"
39 #pragma warning(disable: 4351)
40 // It is safe to ignore the following MSVC warning, which may pop up when T is
41 // a const type: "warning C4512: assignment operator could not be generated".
42 #pragma warning(disable: 4512)
43 #endif
44 #endif
45
46 #ifdef BOOST_NO_COMPLETE_VALUE_INITIALIZATION
47 // Implementation detail: The macro BOOST_DETAIL_VALUE_INIT_WORKAROUND_SUGGESTED
48 // suggests that a workaround should be applied, because of compiler issues
49 // regarding value-initialization.
50 #define BOOST_DETAIL_VALUE_INIT_WORKAROUND_SUGGESTED
51 #endif
52
53 // Implementation detail: The macro BOOST_DETAIL_VALUE_INIT_WORKAROUND
54 // switches the value-initialization workaround either on or off.
55 #ifndef BOOST_DETAIL_VALUE_INIT_WORKAROUND
56 #ifdef BOOST_DETAIL_VALUE_INIT_WORKAROUND_SUGGESTED
57 #define BOOST_DETAIL_VALUE_INIT_WORKAROUND 1
58 #else
59 #define BOOST_DETAIL_VALUE_INIT_WORKAROUND 0
60 #endif
61 #endif
62
63 namespace boost {
64
65 template<class T>
66 class initialized
67 {
68 private :
69 struct wrapper
70 {
71 #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592))
72 typename
73 #endif
74 remove_const<T>::type data;
75
wrapperboost::initialized::wrapper76 wrapper()
77 :
78 data()
79 {
80 }
81
wrapperboost::initialized::wrapper82 wrapper(T const & arg)
83 :
84 data(arg)
85 {
86 }
87 };
88
89 mutable
90 #if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592))
91 typename
92 #endif
93 aligned_storage<sizeof(wrapper), alignment_of<wrapper>::value>::type x;
94
wrapper_address() const95 wrapper * wrapper_address() const
96 {
97 return static_cast<wrapper *>( static_cast<void*>(&x));
98 }
99
100 public :
101
initialized()102 initialized()
103 {
104 #if BOOST_DETAIL_VALUE_INIT_WORKAROUND
105 std::memset(&x, 0, sizeof(x));
106 #endif
107 new (wrapper_address()) wrapper();
108 }
109
initialized(initialized const & arg)110 initialized(initialized const & arg)
111 {
112 new (wrapper_address()) wrapper( static_cast<wrapper const &>(*(arg.wrapper_address())));
113 }
114
initialized(T const & arg)115 explicit initialized(T const & arg)
116 {
117 new (wrapper_address()) wrapper(arg);
118 }
119
operator =(initialized const & arg)120 initialized & operator=(initialized const & arg)
121 {
122 // Assignment is only allowed when T is non-const.
123 BOOST_STATIC_ASSERT( ! is_const<T>::value );
124 *wrapper_address() = static_cast<wrapper const &>(*(arg.wrapper_address()));
125 return *this;
126 }
127
~initialized()128 ~initialized()
129 {
130 wrapper_address()->wrapper::~wrapper();
131 }
132
data() const133 T const & data() const
134 {
135 return wrapper_address()->data;
136 }
137
data()138 T& data()
139 {
140 return wrapper_address()->data;
141 }
142
swap(initialized & arg)143 void swap(initialized & arg)
144 {
145 ::boost::swap( this->data(), arg.data() );
146 }
147
operator T const&() const148 operator T const &() const
149 {
150 return wrapper_address()->data;
151 }
152
operator T&()153 operator T&()
154 {
155 return wrapper_address()->data;
156 }
157
158 } ;
159
160 template<class T>
get(initialized<T> const & x)161 T const& get ( initialized<T> const& x )
162 {
163 return x.data() ;
164 }
165
166 template<class T>
get(initialized<T> & x)167 T& get ( initialized<T>& x )
168 {
169 return x.data() ;
170 }
171
172 template<class T>
swap(initialized<T> & lhs,initialized<T> & rhs)173 void swap ( initialized<T> & lhs, initialized<T> & rhs )
174 {
175 lhs.swap(rhs) ;
176 }
177
178 template<class T>
179 class value_initialized
180 {
181 private :
182
183 // initialized<T> does value-initialization by default.
184 initialized<T> m_data;
185
186 public :
187
value_initialized()188 value_initialized()
189 :
190 m_data()
191 { }
192
data() const193 T const & data() const
194 {
195 return m_data.data();
196 }
197
data()198 T& data()
199 {
200 return m_data.data();
201 }
202
swap(value_initialized & arg)203 void swap(value_initialized & arg)
204 {
205 m_data.swap(arg.m_data);
206 }
207
operator T const&() const208 operator T const &() const
209 {
210 return m_data;
211 }
212
operator T&()213 operator T&()
214 {
215 return m_data;
216 }
217 } ;
218
219
220 template<class T>
get(value_initialized<T> const & x)221 T const& get ( value_initialized<T> const& x )
222 {
223 return x.data() ;
224 }
225
226 template<class T>
get(value_initialized<T> & x)227 T& get ( value_initialized<T>& x )
228 {
229 return x.data() ;
230 }
231
232 template<class T>
swap(value_initialized<T> & lhs,value_initialized<T> & rhs)233 void swap ( value_initialized<T> & lhs, value_initialized<T> & rhs )
234 {
235 lhs.swap(rhs) ;
236 }
237
238
239 class initialized_value_t
240 {
241 public :
242
operator T() const243 template <class T> operator T() const
244 {
245 return initialized<T>().data();
246 }
247 };
248
249 initialized_value_t const initialized_value = {} ;
250
251
252 } // namespace boost
253
254 #ifdef BOOST_MSVC
255 #pragma warning(pop)
256 #endif
257
258 #endif
259