1 // Three-state boolean logic library
2 
3 // Copyright Douglas Gregor 2002-2004. Use, modification and
4 // distribution is subject to the Boost Software License, Version
5 // 1.0. (See accompanying file LICENSE_1_0.txt or copy at
6 // http://www.boost.org/LICENSE_1_0.txt)
7 
8 
9 // For more information, see http://www.boost.org
10 #ifndef BOOST_LOGIC_TRIBOOL_HPP
11 #define BOOST_LOGIC_TRIBOOL_HPP
12 
13 #include <boost/logic/tribool_fwd.hpp>
14 #include <boost/config.hpp>
15 #include <boost/detail/workaround.hpp>
16 
17 #ifdef BOOST_HAS_PRAGMA_ONCE
18 #  pragma once
19 #endif
20 
21 namespace boost { namespace logic {
22 
23 /// INTERNAL ONLY
24 namespace detail {
25 /**
26  * INTERNAL ONLY
27  *
28  * \brief A type used only to uniquely identify the 'indeterminate'
29  * function/keyword.
30  */
31 struct indeterminate_t
32 {
33 #if BOOST_WORKAROUND(__BORLANDC__, < 0x0600)
34   char dummy_; // BCB would use 8 bytes by default
35 #endif
36 };
37 
38 } // end namespace detail
39 
40 /**
41  * INTERNAL ONLY
42  * The type of the 'indeterminate' keyword. This has the same type as the
43  * function 'indeterminate' so that we can recognize when the keyword is
44  * used.
45  */
46 typedef bool (*indeterminate_keyword_t)(tribool, detail::indeterminate_t);
47 
48 /**
49  * \brief Keyword and test function for the indeterminate tribool value
50  *
51  * The \c indeterminate function has a dual role. It's first role is
52  * as a unary function that tells whether the tribool value is in the
53  * "indeterminate" state. It's second role is as a keyword
54  * representing the indeterminate (just like "true" and "false"
55  * represent the true and false states). If you do not like the name
56  * "indeterminate", and would prefer to use a different name, see the
57  * macro \c BOOST_TRIBOOL_THIRD_STATE.
58  *
59  * \returns <tt>x.value == tribool::indeterminate_value</tt>
60  * \throws nothrow
61  */
62 BOOST_CONSTEXPR inline bool
63 indeterminate(tribool x,
64               detail::indeterminate_t dummy = detail::indeterminate_t()) BOOST_NOEXCEPT;
65 
66 /**
67  * \brief A 3-state boolean type.
68  *
69  * 3-state boolean values are either true, false, or
70  * indeterminate.
71  */
72 class tribool
73 {
74 private:
75   /// INTERNAL ONLY
76   struct dummy {
nonnullboost::logic::tribool::dummy77     void nonnull() {};
78   };
79 
80   typedef void (dummy::*safe_bool)();
81 
82 public:
83   /**
84    * Construct a new 3-state boolean value with the value 'false'.
85    *
86    * \throws nothrow
87    */
tribool()88   BOOST_CONSTEXPR tribool() BOOST_NOEXCEPT : value(false_value) {}
89 
90   /**
91    * Construct a new 3-state boolean value with the given boolean
92    * value, which may be \c true or \c false.
93    *
94    * \throws nothrow
95    */
tribool(bool initial_value)96   BOOST_CONSTEXPR tribool(bool initial_value) BOOST_NOEXCEPT : value(initial_value? true_value : false_value) {}
97 
98   /**
99    * Construct a new 3-state boolean value with an indeterminate value.
100    *
101    * \throws nothrow
102    */
tribool(indeterminate_keyword_t)103   BOOST_CONSTEXPR tribool(indeterminate_keyword_t) BOOST_NOEXCEPT : value(indeterminate_value) {}
104 
105   /**
106    * Use a 3-state boolean in a boolean context. Will evaluate true in a
107    * boolean context only when the 3-state boolean is definitely true.
108    *
109    * \returns true if the 3-state boolean is true, false otherwise
110    * \throws nothrow
111    */
operator safe_bool() const112   BOOST_CONSTEXPR operator safe_bool() const BOOST_NOEXCEPT
113   {
114     return value == true_value? &dummy::nonnull : 0;
115   }
116 
117   /**
118    * The actual stored value in this 3-state boolean, which may be false, true,
119    * or indeterminate.
120    */
121   enum value_t { false_value, true_value, indeterminate_value } value;
122 };
123 
124 // Check if the given tribool has an indeterminate value. Also doubles as a
125 // keyword for the 'indeterminate' value
indeterminate(tribool x,detail::indeterminate_t)126 BOOST_CONSTEXPR inline bool indeterminate(tribool x, detail::indeterminate_t) BOOST_NOEXCEPT
127 {
128   return x.value == tribool::indeterminate_value;
129 }
130 
131 /** @defgroup logical Logical operations
132  */
133 //@{
134 /**
135  * \brief Computes the logical negation of a tribool
136  *
137  * \returns the logical negation of the tribool, according to the
138  * table:
139  *  <table border=1>
140  *    <tr>
141  *      <th><center><code>!</code></center></th>
142  *      <th/>
143  *    </tr>
144  *    <tr>
145  *      <th><center>false</center></th>
146  *      <td><center>true</center></td>
147  *    </tr>
148  *    <tr>
149  *      <th><center>true</center></th>
150  *      <td><center>false</center></td>
151  *    </tr>
152  *    <tr>
153  *      <th><center>indeterminate</center></th>
154  *      <td><center>indeterminate</center></td>
155  *    </tr>
156  *  </table>
157  * \throws nothrow
158  */
operator !(tribool x)159 BOOST_CONSTEXPR inline tribool operator!(tribool x) BOOST_NOEXCEPT
160 {
161   return x.value == tribool::false_value? tribool(true)
162         :x.value == tribool::true_value? tribool(false)
163         :tribool(indeterminate);
164 }
165 
166 /**
167  * \brief Computes the logical conjuction of two tribools
168  *
169  * \returns the result of logically ANDing the two tribool values,
170  * according to the following table:
171  *       <table border=1>
172  *           <tr>
173  *             <th><center><code>&amp;&amp;</code></center></th>
174  *             <th><center>false</center></th>
175  *             <th><center>true</center></th>
176  *             <th><center>indeterminate</center></th>
177  *           </tr>
178  *           <tr>
179  *             <th><center>false</center></th>
180  *             <td><center>false</center></td>
181  *             <td><center>false</center></td>
182  *             <td><center>false</center></td>
183  *           </tr>
184  *           <tr>
185  *             <th><center>true</center></th>
186  *             <td><center>false</center></td>
187  *             <td><center>true</center></td>
188  *             <td><center>indeterminate</center></td>
189  *           </tr>
190  *           <tr>
191  *             <th><center>indeterminate</center></th>
192  *             <td><center>false</center></td>
193  *             <td><center>indeterminate</center></td>
194  *             <td><center>indeterminate</center></td>
195  *           </tr>
196  *       </table>
197  * \throws nothrow
198  */
operator &&(tribool x,tribool y)199 BOOST_CONSTEXPR inline tribool operator&&(tribool x, tribool y) BOOST_NOEXCEPT
200 {
201   return (static_cast<bool>(!x) || static_cast<bool>(!y))
202     ? tribool(false)
203     : ((static_cast<bool>(x) && static_cast<bool>(y)) ? tribool(true) : indeterminate)
204   ;
205 }
206 
207 /**
208  * \overload
209  */
operator &&(tribool x,bool y)210 BOOST_CONSTEXPR inline tribool operator&&(tribool x, bool y) BOOST_NOEXCEPT
211 { return y? x : tribool(false); }
212 
213 /**
214  * \overload
215  */
operator &&(bool x,tribool y)216 BOOST_CONSTEXPR inline tribool operator&&(bool x, tribool y) BOOST_NOEXCEPT
217 { return x? y : tribool(false); }
218 
219 /**
220  * \overload
221  */
operator &&(indeterminate_keyword_t,tribool x)222 BOOST_CONSTEXPR inline tribool operator&&(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
223 { return !x? tribool(false) : tribool(indeterminate); }
224 
225 /**
226  * \overload
227  */
operator &&(tribool x,indeterminate_keyword_t)228 BOOST_CONSTEXPR inline tribool operator&&(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
229 { return !x? tribool(false) : tribool(indeterminate); }
230 
231 /**
232  * \brief Computes the logical disjunction of two tribools
233  *
234  * \returns the result of logically ORing the two tribool values,
235  * according to the following table:
236  *       <table border=1>
237  *           <tr>
238  *             <th><center><code>||</code></center></th>
239  *             <th><center>false</center></th>
240  *             <th><center>true</center></th>
241  *             <th><center>indeterminate</center></th>
242  *           </tr>
243  *           <tr>
244  *             <th><center>false</center></th>
245  *             <td><center>false</center></td>
246  *             <td><center>true</center></td>
247  *             <td><center>indeterminate</center></td>
248  *           </tr>
249  *           <tr>
250  *             <th><center>true</center></th>
251  *             <td><center>true</center></td>
252  *             <td><center>true</center></td>
253  *             <td><center>true</center></td>
254  *           </tr>
255  *           <tr>
256  *             <th><center>indeterminate</center></th>
257  *             <td><center>indeterminate</center></td>
258  *             <td><center>true</center></td>
259  *             <td><center>indeterminate</center></td>
260  *           </tr>
261  *       </table>
262  *  \throws nothrow
263  */
operator ||(tribool x,tribool y)264 BOOST_CONSTEXPR inline tribool operator||(tribool x, tribool y) BOOST_NOEXCEPT
265 {
266   return (static_cast<bool>(!x) && static_cast<bool>(!y))
267     ? tribool(false)
268     : ((static_cast<bool>(x) || static_cast<bool>(y)) ? tribool(true) : tribool(indeterminate))
269   ;
270 }
271 
272 /**
273  * \overload
274  */
operator ||(tribool x,bool y)275 BOOST_CONSTEXPR inline tribool operator||(tribool x, bool y) BOOST_NOEXCEPT
276 { return y? tribool(true) : x; }
277 
278 /**
279  * \overload
280  */
operator ||(bool x,tribool y)281 BOOST_CONSTEXPR inline tribool operator||(bool x, tribool y) BOOST_NOEXCEPT
282 { return x? tribool(true) : y; }
283 
284 /**
285  * \overload
286  */
operator ||(indeterminate_keyword_t,tribool x)287 BOOST_CONSTEXPR inline tribool operator||(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
288 { return x? tribool(true) : tribool(indeterminate); }
289 
290 /**
291  * \overload
292  */
operator ||(tribool x,indeterminate_keyword_t)293 BOOST_CONSTEXPR inline tribool operator||(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
294 { return x? tribool(true) : tribool(indeterminate); }
295 //@}
296 
297 /**
298  * \brief Compare tribools for equality
299  *
300  * \returns the result of comparing two tribool values, according to
301  * the following table:
302  *       <table border=1>
303  *          <tr>
304  *            <th><center><code>==</code></center></th>
305  *            <th><center>false</center></th>
306  *            <th><center>true</center></th>
307  *            <th><center>indeterminate</center></th>
308  *          </tr>
309  *          <tr>
310  *            <th><center>false</center></th>
311  *            <td><center>true</center></td>
312  *            <td><center>false</center></td>
313  *            <td><center>indeterminate</center></td>
314  *          </tr>
315  *          <tr>
316  *            <th><center>true</center></th>
317  *            <td><center>false</center></td>
318  *            <td><center>true</center></td>
319  *            <td><center>indeterminate</center></td>
320  *          </tr>
321  *          <tr>
322  *            <th><center>indeterminate</center></th>
323  *            <td><center>indeterminate</center></td>
324  *            <td><center>indeterminate</center></td>
325  *            <td><center>indeterminate</center></td>
326  *          </tr>
327  *      </table>
328  * \throws nothrow
329  */
operator ==(tribool x,tribool y)330 BOOST_CONSTEXPR inline tribool operator==(tribool x, tribool y) BOOST_NOEXCEPT
331 {
332   return (indeterminate(x) || indeterminate(y))
333     ? indeterminate
334     : ((x && y) || (!x && !y))
335   ;
336 }
337 
338 /**
339  * \overload
340  */
operator ==(tribool x,bool y)341 BOOST_CONSTEXPR inline tribool operator==(tribool x, bool y) BOOST_NOEXCEPT { return x == tribool(y); }
342 
343 /**
344  * \overload
345  */
operator ==(bool x,tribool y)346 BOOST_CONSTEXPR inline tribool operator==(bool x, tribool y) BOOST_NOEXCEPT { return tribool(x) == y; }
347 
348 /**
349  * \overload
350  */
operator ==(indeterminate_keyword_t,tribool x)351 BOOST_CONSTEXPR inline tribool operator==(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
352 { return tribool(indeterminate) == x; }
353 
354 /**
355  * \overload
356  */
operator ==(tribool x,indeterminate_keyword_t)357 BOOST_CONSTEXPR inline tribool operator==(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
358 { return tribool(indeterminate) == x; }
359 
360 /**
361  * \brief Compare tribools for inequality
362  *
363  * \returns the result of comparing two tribool values for inequality,
364  * according to the following table:
365  *       <table border=1>
366  *           <tr>
367  *             <th><center><code>!=</code></center></th>
368  *             <th><center>false</center></th>
369  *             <th><center>true</center></th>
370  *             <th><center>indeterminate</center></th>
371  *           </tr>
372  *           <tr>
373  *             <th><center>false</center></th>
374  *             <td><center>false</center></td>
375  *             <td><center>true</center></td>
376  *             <td><center>indeterminate</center></td>
377  *           </tr>
378  *           <tr>
379  *             <th><center>true</center></th>
380  *             <td><center>true</center></td>
381  *             <td><center>false</center></td>
382  *             <td><center>indeterminate</center></td>
383  *           </tr>
384  *           <tr>
385  *             <th><center>indeterminate</center></th>
386  *             <td><center>indeterminate</center></td>
387  *             <td><center>indeterminate</center></td>
388  *             <td><center>indeterminate</center></td>
389  *           </tr>
390  *       </table>
391  * \throws nothrow
392  */
operator !=(tribool x,tribool y)393 BOOST_CONSTEXPR inline tribool operator!=(tribool x, tribool y) BOOST_NOEXCEPT
394 {
395   return (indeterminate(x) || indeterminate(y))
396     ? indeterminate
397     : !((x && y) || (!x && !y))
398   ;
399 }
400 
401 /**
402  * \overload
403  */
operator !=(tribool x,bool y)404 BOOST_CONSTEXPR inline tribool operator!=(tribool x, bool y) BOOST_NOEXCEPT { return x != tribool(y); }
405 
406 /**
407  * \overload
408  */
operator !=(bool x,tribool y)409 BOOST_CONSTEXPR inline tribool operator!=(bool x, tribool y) BOOST_NOEXCEPT { return tribool(x) != y; }
410 
411 /**
412  * \overload
413  */
operator !=(indeterminate_keyword_t,tribool x)414 BOOST_CONSTEXPR inline tribool operator!=(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
415 { return tribool(indeterminate) != x; }
416 
417 /**
418  * \overload
419  */
operator !=(tribool x,indeterminate_keyword_t)420 BOOST_CONSTEXPR inline tribool operator!=(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
421 { return x != tribool(indeterminate); }
422 
423 } } // end namespace boost::logic
424 
425 // Pull tribool and indeterminate into namespace "boost"
426 namespace boost {
427   using logic::tribool;
428   using logic::indeterminate;
429 }
430 
431 /**
432  * \brief Declare a new name for the third state of a tribool
433  *
434  * Use this macro to declare a new name for the third state of a
435  * tribool. This state can have any number of new names (in addition
436  * to \c indeterminate), all of which will be equivalent. The new name will be
437  * placed in the namespace in which the macro is expanded.
438  *
439  * Example:
440  *   BOOST_TRIBOOL_THIRD_STATE(true_or_false)
441  *
442  *   tribool x(true_or_false);
443  *   // potentially set x
444  *   if (true_or_false(x)) {
445  *     // don't know what x is
446  *   }
447  */
448 #define BOOST_TRIBOOL_THIRD_STATE(Name)                                 \
449 inline bool                                                             \
450 Name(boost::logic::tribool x,                                           \
451      boost::logic::detail::indeterminate_t =                            \
452        boost::logic::detail::indeterminate_t())                         \
453 { return x.value == boost::logic::tribool::indeterminate_value; }
454 
455 #endif // BOOST_LOGIC_TRIBOOL_HPP
456 
457