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1 // Three-state boolean logic library |
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2 |
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3 // Copyright Douglas Gregor 2002-2004. Use, modification and |
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4 // distribution is subject to the Boost Software License, Version |
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5 // 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
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6 // http://www.boost.org/LICENSE_1_0.txt) |
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7 |
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8 |
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9 // For more information, see http://www.boost.org |
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10 #ifndef BOOST_LOGIC_TRIBOOL_HPP |
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11 #define BOOST_LOGIC_TRIBOOL_HPP |
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12 |
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13 #include <boost/logic/tribool_fwd.hpp> |
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14 #include <boost/config.hpp> |
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15 #include <boost/detail/workaround.hpp> |
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16 |
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17 #if BOOST_WORKAROUND(_MSC_VER, >= 1200) |
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18 # pragma once |
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19 #endif |
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20 |
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21 namespace boost { namespace logic { |
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22 |
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23 /// INTERNAL ONLY |
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24 namespace detail { |
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25 /** |
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26 * INTERNAL ONLY |
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27 * |
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28 * \brief A type used only to uniquely identify the 'indeterminate' |
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29 * function/keyword. |
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30 */ |
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31 struct indeterminate_t |
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32 { |
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33 #if BOOST_WORKAROUND(__BORLANDC__, < 0x0600) |
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34 char dummy_; // BCB would use 8 bytes by default |
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35 #endif |
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36 }; |
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37 |
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38 } // end namespace detail |
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39 |
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40 /** |
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41 * INTERNAL ONLY |
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42 * The type of the 'indeterminate' keyword. This has the same type as the |
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43 * function 'indeterminate' so that we can recognize when the keyword is |
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44 * used. |
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45 */ |
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46 typedef bool (*indeterminate_keyword_t)(tribool, detail::indeterminate_t); |
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47 |
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48 /** |
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49 * \brief Keyword and test function for the indeterminate tribool value |
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50 * |
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51 * The \c indeterminate function has a dual role. It's first role is |
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52 * as a unary function that tells whether the tribool value is in the |
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53 * "indeterminate" state. It's second role is as a keyword |
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54 * representing the indeterminate (just like "true" and "false" |
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55 * represent the true and false states). If you do not like the name |
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56 * "indeterminate", and would prefer to use a different name, see the |
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57 * macro \c BOOST_TRIBOOL_THIRD_STATE. |
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58 * |
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59 * \returns <tt>x.value == tribool::indeterminate_value</tt> |
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60 * \throws nothrow |
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61 */ |
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62 inline bool |
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63 indeterminate(tribool x, |
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64 detail::indeterminate_t dummy = detail::indeterminate_t()); |
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65 |
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66 /** |
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67 * \brief A 3-state boolean type. |
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68 * |
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69 * 3-state boolean values are either true, false, or |
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70 * indeterminate. |
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71 */ |
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72 class tribool |
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73 { |
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74 private: |
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75 /// INTERNAL ONLY |
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76 struct dummy { |
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77 void nonnull() {}; |
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78 }; |
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79 |
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80 typedef void (dummy::*safe_bool)(); |
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81 |
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82 public: |
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83 /** |
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84 * Construct a new 3-state boolean value with the value 'false'. |
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85 * |
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86 * \throws nothrow |
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87 */ |
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88 tribool() : value(false_value) {} |
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89 |
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90 /** |
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91 * Construct a new 3-state boolean value with the given boolean |
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92 * value, which may be \c true or \c false. |
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93 * |
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94 * \throws nothrow |
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95 */ |
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96 tribool(bool value) : value(value? true_value : false_value) {} |
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97 |
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98 /** |
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99 * Construct a new 3-state boolean value with an indeterminate value. |
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100 * |
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101 * \throws nothrow |
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102 */ |
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103 tribool(indeterminate_keyword_t) : value(indeterminate_value) {} |
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104 |
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105 /** |
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106 * Use a 3-state boolean in a boolean context. Will evaluate true in a |
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107 * boolean context only when the 3-state boolean is definitely true. |
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108 * |
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109 * \returns true if the 3-state boolean is true, false otherwise |
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110 * \throws nothrow |
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111 */ |
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112 operator safe_bool() const |
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113 { |
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114 return value == true_value? &dummy::nonnull : 0; |
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115 } |
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116 |
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117 /** |
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118 * The actual stored value in this 3-state boolean, which may be false, true, |
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119 * or indeterminate. |
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120 */ |
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121 enum value_t { false_value, true_value, indeterminate_value } value; |
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122 }; |
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123 |
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124 // Check if the given tribool has an indeterminate value. Also doubles as a |
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125 // keyword for the 'indeterminate' value |
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126 inline bool indeterminate(tribool x, detail::indeterminate_t) |
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127 { |
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128 return x.value == tribool::indeterminate_value; |
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129 } |
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130 |
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131 /** @defgroup logical Logical operations |
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132 */ |
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133 //@{ |
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134 /** |
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135 * \brief Computes the logical negation of a tribool |
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136 * |
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137 * \returns the logical negation of the tribool, according to the |
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138 * table: |
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139 * <table border=1> |
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140 * <tr> |
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141 * <th><center><code>!</code></center></th> |
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142 * <th/> |
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143 * </tr> |
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144 * <tr> |
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145 * <th><center>false</center></th> |
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146 * <td><center>true</center></td> |
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147 * </tr> |
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148 * <tr> |
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149 * <th><center>true</center></th> |
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150 * <td><center>false</center></td> |
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151 * </tr> |
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152 * <tr> |
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153 * <th><center>indeterminate</center></th> |
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154 * <td><center>indeterminate</center></td> |
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155 * </tr> |
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156 * </table> |
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157 * \throws nothrow |
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158 */ |
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159 inline tribool operator!(tribool x) |
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160 { |
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161 return x.value == tribool::false_value? tribool(true) |
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162 :x.value == tribool::true_value? tribool(false) |
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163 :tribool(indeterminate); |
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164 } |
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165 |
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166 /** |
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167 * \brief Computes the logical conjuction of two tribools |
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168 * |
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169 * \returns the result of logically ANDing the two tribool values, |
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170 * according to the following table: |
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171 * <table border=1> |
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172 * <tr> |
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173 * <th><center><code>&&</code></center></th> |
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174 * <th><center>false</center></th> |
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175 * <th><center>true</center></th> |
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176 * <th><center>indeterminate</center></th> |
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177 * </tr> |
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178 * <tr> |
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179 * <th><center>false</center></th> |
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180 * <td><center>false</center></td> |
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181 * <td><center>false</center></td> |
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182 * <td><center>false</center></td> |
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183 * </tr> |
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184 * <tr> |
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185 * <th><center>true</center></th> |
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186 * <td><center>false</center></td> |
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187 * <td><center>true</center></td> |
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188 * <td><center>indeterminate</center></td> |
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189 * </tr> |
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190 * <tr> |
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191 * <th><center>indeterminate</center></th> |
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192 * <td><center>false</center></td> |
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193 * <td><center>indeterminate</center></td> |
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194 * <td><center>indeterminate</center></td> |
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195 * </tr> |
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196 * </table> |
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197 * \throws nothrow |
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198 */ |
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199 inline tribool operator&&(tribool x, tribool y) |
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200 { |
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201 if (static_cast<bool>(!x) || static_cast<bool>(!y)) |
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202 return false; |
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203 else if (static_cast<bool>(x) && static_cast<bool>(y)) |
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204 return true; |
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205 else |
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206 return indeterminate; |
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207 } |
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208 |
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209 /** |
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210 * \overload |
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211 */ |
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212 inline tribool operator&&(tribool x, bool y) |
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213 { return y? x : tribool(false); } |
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214 |
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215 /** |
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216 * \overload |
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217 */ |
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218 inline tribool operator&&(bool x, tribool y) |
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219 { return x? y : tribool(false); } |
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220 |
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221 /** |
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222 * \overload |
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223 */ |
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224 inline tribool operator&&(indeterminate_keyword_t, tribool x) |
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225 { return !x? tribool(false) : tribool(indeterminate); } |
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226 |
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227 /** |
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228 * \overload |
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229 */ |
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230 inline tribool operator&&(tribool x, indeterminate_keyword_t) |
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231 { return !x? tribool(false) : tribool(indeterminate); } |
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232 |
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233 /** |
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234 * \brief Computes the logical disjunction of two tribools |
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235 * |
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236 * \returns the result of logically ORing the two tribool values, |
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237 * according to the following table: |
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238 * <table border=1> |
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239 * <tr> |
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240 * <th><center><code>||</code></center></th> |
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241 * <th><center>false</center></th> |
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242 * <th><center>true</center></th> |
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243 * <th><center>indeterminate</center></th> |
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244 * </tr> |
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245 * <tr> |
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246 * <th><center>false</center></th> |
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247 * <td><center>false</center></td> |
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248 * <td><center>true</center></td> |
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249 * <td><center>indeterminate</center></td> |
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250 * </tr> |
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251 * <tr> |
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252 * <th><center>true</center></th> |
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253 * <td><center>true</center></td> |
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254 * <td><center>true</center></td> |
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255 * <td><center>true</center></td> |
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256 * </tr> |
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257 * <tr> |
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258 * <th><center>indeterminate</center></th> |
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259 * <td><center>indeterminate</center></td> |
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260 * <td><center>true</center></td> |
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261 * <td><center>indeterminate</center></td> |
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262 * </tr> |
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263 * </table> |
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264 * \throws nothrow |
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265 */ |
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266 inline tribool operator||(tribool x, tribool y) |
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267 { |
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268 if (static_cast<bool>(!x) && static_cast<bool>(!y)) |
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269 return false; |
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270 else if (static_cast<bool>(x) || static_cast<bool>(y)) |
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271 return true; |
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272 else |
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273 return indeterminate; |
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274 } |
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275 |
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276 /** |
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277 * \overload |
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278 */ |
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279 inline tribool operator||(tribool x, bool y) |
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280 { return y? tribool(true) : x; } |
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281 |
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282 /** |
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283 * \overload |
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284 */ |
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285 inline tribool operator||(bool x, tribool y) |
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286 { return x? tribool(true) : y; } |
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287 |
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288 /** |
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289 * \overload |
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290 */ |
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291 inline tribool operator||(indeterminate_keyword_t, tribool x) |
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292 { return x? tribool(true) : tribool(indeterminate); } |
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293 |
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294 /** |
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295 * \overload |
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296 */ |
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297 inline tribool operator||(tribool x, indeterminate_keyword_t) |
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298 { return x? tribool(true) : tribool(indeterminate); } |
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299 //@} |
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300 |
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301 /** |
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302 * \brief Compare tribools for equality |
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303 * |
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304 * \returns the result of comparing two tribool values, according to |
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305 * the following table: |
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306 * <table border=1> |
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307 * <tr> |
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308 * <th><center><code>==</code></center></th> |
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309 * <th><center>false</center></th> |
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310 * <th><center>true</center></th> |
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311 * <th><center>indeterminate</center></th> |
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312 * </tr> |
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313 * <tr> |
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314 * <th><center>false</center></th> |
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315 * <td><center>true</center></td> |
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316 * <td><center>false</center></td> |
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317 * <td><center>indeterminate</center></td> |
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318 * </tr> |
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319 * <tr> |
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320 * <th><center>true</center></th> |
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321 * <td><center>false</center></td> |
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322 * <td><center>true</center></td> |
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323 * <td><center>indeterminate</center></td> |
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324 * </tr> |
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325 * <tr> |
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326 * <th><center>indeterminate</center></th> |
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327 * <td><center>indeterminate</center></td> |
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328 * <td><center>indeterminate</center></td> |
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329 * <td><center>indeterminate</center></td> |
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330 * </tr> |
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331 * </table> |
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332 * \throws nothrow |
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333 */ |
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334 inline tribool operator==(tribool x, tribool y) |
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335 { |
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336 if (indeterminate(x) || indeterminate(y)) |
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337 return indeterminate; |
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338 else |
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339 return x && y || !x && !y; |
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340 } |
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341 |
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342 /** |
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343 * \overload |
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344 */ |
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345 inline tribool operator==(tribool x, bool y) { return x == tribool(y); } |
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346 |
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347 /** |
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348 * \overload |
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349 */ |
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350 inline tribool operator==(bool x, tribool y) { return tribool(x) == y; } |
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351 |
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352 /** |
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353 * \overload |
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354 */ |
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355 inline tribool operator==(indeterminate_keyword_t, tribool x) |
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356 { return tribool(indeterminate) == x; } |
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357 |
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358 /** |
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359 * \overload |
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360 */ |
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361 inline tribool operator==(tribool x, indeterminate_keyword_t) |
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362 { return tribool(indeterminate) == x; } |
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363 |
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364 /** |
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365 * \brief Compare tribools for inequality |
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366 * |
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367 * \returns the result of comparing two tribool values for inequality, |
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368 * according to the following table: |
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369 * <table border=1> |
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370 * <tr> |
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371 * <th><center><code>!=</code></center></th> |
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372 * <th><center>false</center></th> |
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373 * <th><center>true</center></th> |
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374 * <th><center>indeterminate</center></th> |
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375 * </tr> |
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376 * <tr> |
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377 * <th><center>false</center></th> |
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378 * <td><center>false</center></td> |
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379 * <td><center>true</center></td> |
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380 * <td><center>indeterminate</center></td> |
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381 * </tr> |
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382 * <tr> |
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383 * <th><center>true</center></th> |
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384 * <td><center>true</center></td> |
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385 * <td><center>false</center></td> |
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386 * <td><center>indeterminate</center></td> |
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387 * </tr> |
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388 * <tr> |
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389 * <th><center>indeterminate</center></th> |
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390 * <td><center>indeterminate</center></td> |
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391 * <td><center>indeterminate</center></td> |
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392 * <td><center>indeterminate</center></td> |
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393 * </tr> |
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394 * </table> |
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395 * \throws nothrow |
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396 */ |
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397 inline tribool operator!=(tribool x, tribool y) |
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398 { |
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399 if (indeterminate(x) || indeterminate(y)) |
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400 return indeterminate; |
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401 else |
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402 return !(x && y || !x && !y); |
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403 } |
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404 |
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405 /** |
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406 * \overload |
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407 */ |
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408 inline tribool operator!=(tribool x, bool y) { return x != tribool(y); } |
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409 |
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410 /** |
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411 * \overload |
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412 */ |
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413 inline tribool operator!=(bool x, tribool y) { return tribool(x) != y; } |
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414 |
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415 /** |
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416 * \overload |
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417 */ |
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418 inline tribool operator!=(indeterminate_keyword_t, tribool x) |
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419 { return tribool(indeterminate) != x; } |
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420 |
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421 /** |
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422 * \overload |
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423 */ |
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424 inline tribool operator!=(tribool x, indeterminate_keyword_t) |
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425 { return x != tribool(indeterminate); } |
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426 |
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427 } } // end namespace boost::logic |
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428 |
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429 // Pull tribool and indeterminate into namespace "boost" |
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430 namespace boost { |
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431 using logic::tribool; |
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432 using logic::indeterminate; |
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433 } |
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434 |
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435 /** |
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436 * \brief Declare a new name for the third state of a tribool |
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437 * |
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438 * Use this macro to declare a new name for the third state of a |
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439 * tribool. This state can have any number of new names (in addition |
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440 * to \c indeterminate), all of which will be equivalent. The new name will be |
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441 * placed in the namespace in which the macro is expanded. |
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442 * |
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443 * Example: |
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444 * BOOST_TRIBOOL_THIRD_STATE(true_or_false) |
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445 * |
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446 * tribool x(true_or_false); |
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447 * // potentially set x |
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448 * if (true_or_false(x)) { |
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449 * // don't know what x is |
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450 * } |
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451 */ |
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452 #define BOOST_TRIBOOL_THIRD_STATE(Name) \ |
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453 inline bool \ |
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454 Name(boost::logic::tribool x, \ |
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455 boost::logic::detail::indeterminate_t dummy = \ |
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456 boost::logic::detail::indeterminate_t()) \ |
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457 { return x.value == boost::logic::tribool::indeterminate_value; } |
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458 |
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459 #endif // BOOST_LOGIC_TRIBOOL_HPP |
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460 |