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
21namespace boost { namespace logic {
22
23/// INTERNAL ONLY
24namespace detail {
25/**
26 * INTERNAL ONLY
27 *
28 * \brief A type used only to uniquely identify the 'indeterminate'
29 * function/keyword.
30 */
31struct indeterminate_t
32{
33#if BOOST_WORKAROUND(BOOST_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 */
46typedef 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 */
62BOOST_CONSTEXPR inline bool
63indeterminate(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 */
72class tribool
73{
74#if defined( BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS )
75private:
76 /// INTERNAL ONLY
77 struct dummy {
78 void nonnull() {};
79 };
80
81 typedef void (dummy::*safe_bool)();
82#endif
83
84public:
85 /**
86 * Construct a new 3-state boolean value with the value 'false'.
87 *
88 * \throws nothrow
89 */
90 BOOST_CONSTEXPR tribool() BOOST_NOEXCEPT : value(false_value) {}
91
92 /**
93 * Construct a new 3-state boolean value with the given boolean
94 * value, which may be \c true or \c false.
95 *
96 * \throws nothrow
97 */
98 BOOST_CONSTEXPR tribool(bool initial_value) BOOST_NOEXCEPT : value(initial_value? true_value : false_value) {}
99
100 /**
101 * Construct a new 3-state boolean value with an indeterminate value.
102 *
103 * \throws nothrow
104 */
105 BOOST_CONSTEXPR tribool(indeterminate_keyword_t) BOOST_NOEXCEPT : value(indeterminate_value) {}
106
107 /**
108 * Use a 3-state boolean in a boolean context. Will evaluate true in a
109 * boolean context only when the 3-state boolean is definitely true.
110 *
111 * \returns true if the 3-state boolean is true, false otherwise
112 * \throws nothrow
113 */
114#if !defined( BOOST_NO_CXX11_EXPLICIT_CONVERSION_OPERATORS )
115
116 BOOST_CONSTEXPR explicit operator bool () const BOOST_NOEXCEPT
117 {
118 return value == true_value;
119 }
120
121#else
122
123 BOOST_CONSTEXPR operator safe_bool() const BOOST_NOEXCEPT
124 {
125 return value == true_value? &dummy::nonnull : 0;
126 }
127
128#endif
129
130 /**
131 * The actual stored value in this 3-state boolean, which may be false, true,
132 * or indeterminate.
133 */
134 enum value_t { false_value, true_value, indeterminate_value } value;
135};
136
137// Check if the given tribool has an indeterminate value. Also doubles as a
138// keyword for the 'indeterminate' value
139BOOST_CONSTEXPR inline bool indeterminate(tribool x, detail::indeterminate_t) BOOST_NOEXCEPT
140{
141 return x.value == tribool::indeterminate_value;
142}
143
144/** @defgroup logical Logical operations
145 */
146//@{
147/**
148 * \brief Computes the logical negation of a tribool
149 *
150 * \returns the logical negation of the tribool, according to the
151 * table:
152 * <table border=1>
153 * <tr>
154 * <th><center><code>!</code></center></th>
155 * <th/>
156 * </tr>
157 * <tr>
158 * <th><center>false</center></th>
159 * <td><center>true</center></td>
160 * </tr>
161 * <tr>
162 * <th><center>true</center></th>
163 * <td><center>false</center></td>
164 * </tr>
165 * <tr>
166 * <th><center>indeterminate</center></th>
167 * <td><center>indeterminate</center></td>
168 * </tr>
169 * </table>
170 * \throws nothrow
171 */
172BOOST_CONSTEXPR inline tribool operator!(tribool x) BOOST_NOEXCEPT
173{
174 return x.value == tribool::false_value? tribool(true)
175 :x.value == tribool::true_value? tribool(false)
176 :tribool(indeterminate);
177}
178
179/**
180 * \brief Computes the logical conjunction of two tribools
181 *
182 * \returns the result of logically ANDing the two tribool values,
183 * according to the following table:
184 * <table border=1>
185 * <tr>
186 * <th><center><code>&amp;&amp;</code></center></th>
187 * <th><center>false</center></th>
188 * <th><center>true</center></th>
189 * <th><center>indeterminate</center></th>
190 * </tr>
191 * <tr>
192 * <th><center>false</center></th>
193 * <td><center>false</center></td>
194 * <td><center>false</center></td>
195 * <td><center>false</center></td>
196 * </tr>
197 * <tr>
198 * <th><center>true</center></th>
199 * <td><center>false</center></td>
200 * <td><center>true</center></td>
201 * <td><center>indeterminate</center></td>
202 * </tr>
203 * <tr>
204 * <th><center>indeterminate</center></th>
205 * <td><center>false</center></td>
206 * <td><center>indeterminate</center></td>
207 * <td><center>indeterminate</center></td>
208 * </tr>
209 * </table>
210 * \throws nothrow
211 */
212BOOST_CONSTEXPR inline tribool operator&&(tribool x, tribool y) BOOST_NOEXCEPT
213{
214 return (static_cast<bool>(!x) || static_cast<bool>(!y))
215 ? tribool(false)
216 : ((static_cast<bool>(x) && static_cast<bool>(y)) ? tribool(true) : indeterminate)
217 ;
218}
219
220/**
221 * \overload
222 */
223BOOST_CONSTEXPR inline tribool operator&&(tribool x, bool y) BOOST_NOEXCEPT
224{ return y? x : tribool(false); }
225
226/**
227 * \overload
228 */
229BOOST_CONSTEXPR inline tribool operator&&(bool x, tribool y) BOOST_NOEXCEPT
230{ return x? y : tribool(false); }
231
232/**
233 * \overload
234 */
235BOOST_CONSTEXPR inline tribool operator&&(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
236{ return !x? tribool(false) : tribool(indeterminate); }
237
238/**
239 * \overload
240 */
241BOOST_CONSTEXPR inline tribool operator&&(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
242{ return !x? tribool(false) : tribool(indeterminate); }
243
244/**
245 * \brief Computes the logical disjunction of two tribools
246 *
247 * \returns the result of logically ORing the two tribool values,
248 * according to the following table:
249 * <table border=1>
250 * <tr>
251 * <th><center><code>||</code></center></th>
252 * <th><center>false</center></th>
253 * <th><center>true</center></th>
254 * <th><center>indeterminate</center></th>
255 * </tr>
256 * <tr>
257 * <th><center>false</center></th>
258 * <td><center>false</center></td>
259 * <td><center>true</center></td>
260 * <td><center>indeterminate</center></td>
261 * </tr>
262 * <tr>
263 * <th><center>true</center></th>
264 * <td><center>true</center></td>
265 * <td><center>true</center></td>
266 * <td><center>true</center></td>
267 * </tr>
268 * <tr>
269 * <th><center>indeterminate</center></th>
270 * <td><center>indeterminate</center></td>
271 * <td><center>true</center></td>
272 * <td><center>indeterminate</center></td>
273 * </tr>
274 * </table>
275 * \throws nothrow
276 */
277BOOST_CONSTEXPR inline tribool operator||(tribool x, tribool y) BOOST_NOEXCEPT
278{
279 return (static_cast<bool>(!x) && static_cast<bool>(!y))
280 ? tribool(false)
281 : ((static_cast<bool>(x) || static_cast<bool>(y)) ? tribool(true) : tribool(indeterminate))
282 ;
283}
284
285/**
286 * \overload
287 */
288BOOST_CONSTEXPR inline tribool operator||(tribool x, bool y) BOOST_NOEXCEPT
289{ return y? tribool(true) : x; }
290
291/**
292 * \overload
293 */
294BOOST_CONSTEXPR inline tribool operator||(bool x, tribool y) BOOST_NOEXCEPT
295{ return x? tribool(true) : y; }
296
297/**
298 * \overload
299 */
300BOOST_CONSTEXPR inline tribool operator||(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
301{ return x? tribool(true) : tribool(indeterminate); }
302
303/**
304 * \overload
305 */
306BOOST_CONSTEXPR inline tribool operator||(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
307{ return x? tribool(true) : tribool(indeterminate); }
308//@}
309
310/**
311 * \brief Compare tribools for equality
312 *
313 * \returns the result of comparing two tribool values, according to
314 * the following table:
315 * <table border=1>
316 * <tr>
317 * <th><center><code>==</code></center></th>
318 * <th><center>false</center></th>
319 * <th><center>true</center></th>
320 * <th><center>indeterminate</center></th>
321 * </tr>
322 * <tr>
323 * <th><center>false</center></th>
324 * <td><center>true</center></td>
325 * <td><center>false</center></td>
326 * <td><center>indeterminate</center></td>
327 * </tr>
328 * <tr>
329 * <th><center>true</center></th>
330 * <td><center>false</center></td>
331 * <td><center>true</center></td>
332 * <td><center>indeterminate</center></td>
333 * </tr>
334 * <tr>
335 * <th><center>indeterminate</center></th>
336 * <td><center>indeterminate</center></td>
337 * <td><center>indeterminate</center></td>
338 * <td><center>indeterminate</center></td>
339 * </tr>
340 * </table>
341 * \throws nothrow
342 */
343BOOST_CONSTEXPR inline tribool operator==(tribool x, tribool y) BOOST_NOEXCEPT
344{
345 return (indeterminate(x) || indeterminate(x: y))
346 ? indeterminate
347 : ((x && y) || (!x && !y))
348 ;
349}
350
351/**
352 * \overload
353 */
354BOOST_CONSTEXPR inline tribool operator==(tribool x, bool y) BOOST_NOEXCEPT { return x == tribool(y); }
355
356/**
357 * \overload
358 */
359BOOST_CONSTEXPR inline tribool operator==(bool x, tribool y) BOOST_NOEXCEPT { return tribool(x) == y; }
360
361/**
362 * \overload
363 */
364BOOST_CONSTEXPR inline tribool operator==(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
365{ return tribool(indeterminate) == x; }
366
367/**
368 * \overload
369 */
370BOOST_CONSTEXPR inline tribool operator==(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
371{ return tribool(indeterminate) == x; }
372
373/**
374 * \brief Compare tribools for inequality
375 *
376 * \returns the result of comparing two tribool values for inequality,
377 * according to the following table:
378 * <table border=1>
379 * <tr>
380 * <th><center><code>!=</code></center></th>
381 * <th><center>false</center></th>
382 * <th><center>true</center></th>
383 * <th><center>indeterminate</center></th>
384 * </tr>
385 * <tr>
386 * <th><center>false</center></th>
387 * <td><center>false</center></td>
388 * <td><center>true</center></td>
389 * <td><center>indeterminate</center></td>
390 * </tr>
391 * <tr>
392 * <th><center>true</center></th>
393 * <td><center>true</center></td>
394 * <td><center>false</center></td>
395 * <td><center>indeterminate</center></td>
396 * </tr>
397 * <tr>
398 * <th><center>indeterminate</center></th>
399 * <td><center>indeterminate</center></td>
400 * <td><center>indeterminate</center></td>
401 * <td><center>indeterminate</center></td>
402 * </tr>
403 * </table>
404 * \throws nothrow
405 */
406BOOST_CONSTEXPR inline tribool operator!=(tribool x, tribool y) BOOST_NOEXCEPT
407{
408 return (indeterminate(x) || indeterminate(x: y))
409 ? indeterminate
410 : !((x && y) || (!x && !y))
411 ;
412}
413
414/**
415 * \overload
416 */
417BOOST_CONSTEXPR inline tribool operator!=(tribool x, bool y) BOOST_NOEXCEPT { return x != tribool(y); }
418
419/**
420 * \overload
421 */
422BOOST_CONSTEXPR inline tribool operator!=(bool x, tribool y) BOOST_NOEXCEPT { return tribool(x) != y; }
423
424/**
425 * \overload
426 */
427BOOST_CONSTEXPR inline tribool operator!=(indeterminate_keyword_t, tribool x) BOOST_NOEXCEPT
428{ return tribool(indeterminate) != x; }
429
430/**
431 * \overload
432 */
433BOOST_CONSTEXPR inline tribool operator!=(tribool x, indeterminate_keyword_t) BOOST_NOEXCEPT
434{ return x != tribool(indeterminate); }
435
436} } // end namespace boost::logic
437
438// Pull tribool and indeterminate into namespace "boost"
439namespace boost {
440 using logic::tribool;
441 using logic::indeterminate;
442}
443
444/**
445 * \brief Declare a new name for the third state of a tribool
446 *
447 * Use this macro to declare a new name for the third state of a
448 * tribool. This state can have any number of new names (in addition
449 * to \c indeterminate), all of which will be equivalent. The new name will be
450 * placed in the namespace in which the macro is expanded.
451 *
452 * Example:
453 * BOOST_TRIBOOL_THIRD_STATE(true_or_false)
454 *
455 * tribool x(true_or_false);
456 * // potentially set x
457 * if (true_or_false(x)) {
458 * // don't know what x is
459 * }
460 */
461#define BOOST_TRIBOOL_THIRD_STATE(Name) \
462inline bool \
463Name(boost::logic::tribool x, \
464 boost::logic::detail::indeterminate_t = \
465 boost::logic::detail::indeterminate_t()) \
466{ return x.value == boost::logic::tribool::indeterminate_value; }
467
468#endif // BOOST_LOGIC_TRIBOOL_HPP
469
470

source code of boost/libs/logic/include/boost/logic/tribool.hpp