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