1 | // The -*- C++ -*- type traits classes for internal use in libstdc++ |
2 | |
3 | // Copyright (C) 2000-2022 Free Software Foundation, Inc. |
4 | // |
5 | // This file is part of the GNU ISO C++ Library. This library is free |
6 | // software; you can redistribute it and/or modify it under the |
7 | // terms of the GNU General Public License as published by the |
8 | // Free Software Foundation; either version 3, or (at your option) |
9 | // any later version. |
10 | |
11 | // This library is distributed in the hope that it will be useful, |
12 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
13 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
14 | // GNU General Public License for more details. |
15 | |
16 | // Under Section 7 of GPL version 3, you are granted additional |
17 | // permissions described in the GCC Runtime Library Exception, version |
18 | // 3.1, as published by the Free Software Foundation. |
19 | |
20 | // You should have received a copy of the GNU General Public License and |
21 | // a copy of the GCC Runtime Library Exception along with this program; |
22 | // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
23 | // <http://www.gnu.org/licenses/>. |
24 | |
25 | /** @file bits/cpp_type_traits.h |
26 | * This is an internal header file, included by other library headers. |
27 | * Do not attempt to use it directly. @headername{ext/type_traits} |
28 | */ |
29 | |
30 | // Written by Gabriel Dos Reis <dosreis@cmla.ens-cachan.fr> |
31 | |
32 | #ifndef _CPP_TYPE_TRAITS_H |
33 | #define _CPP_TYPE_TRAITS_H 1 |
34 | |
35 | #pragma GCC system_header |
36 | |
37 | #include <bits/c++config.h> |
38 | |
39 | // |
40 | // This file provides some compile-time information about various types. |
41 | // These representations were designed, on purpose, to be constant-expressions |
42 | // and not types as found in <bits/type_traits.h>. In particular, they |
43 | // can be used in control structures and the optimizer hopefully will do |
44 | // the obvious thing. |
45 | // |
46 | // Why integral expressions, and not functions nor types? |
47 | // Firstly, these compile-time entities are used as template-arguments |
48 | // so function return values won't work: We need compile-time entities. |
49 | // We're left with types and constant integral expressions. |
50 | // Secondly, from the point of view of ease of use, type-based compile-time |
51 | // information is -not- *that* convenient. One has to write lots of |
52 | // overloaded functions and to hope that the compiler will select the right |
53 | // one. As a net effect, the overall structure isn't very clear at first |
54 | // glance. |
55 | // Thirdly, partial ordering and overload resolution (of function templates) |
56 | // is highly costly in terms of compiler-resource. It is a Good Thing to |
57 | // keep these resource consumption as least as possible. |
58 | // |
59 | // See valarray_array.h for a case use. |
60 | // |
61 | // -- Gaby (dosreis@cmla.ens-cachan.fr) 2000-03-06. |
62 | // |
63 | // Update 2005: types are also provided and <bits/type_traits.h> has been |
64 | // removed. |
65 | // |
66 | |
67 | extern "C++" { |
68 | |
69 | namespace std _GLIBCXX_VISIBILITY(default) |
70 | { |
71 | _GLIBCXX_BEGIN_NAMESPACE_VERSION |
72 | |
73 | struct __true_type { }; |
74 | struct __false_type { }; |
75 | |
76 | template<bool> |
77 | struct __truth_type |
78 | { typedef __false_type __type; }; |
79 | |
80 | template<> |
81 | struct __truth_type<true> |
82 | { typedef __true_type __type; }; |
83 | |
84 | // N.B. The conversions to bool are needed due to the issue |
85 | // explained in c++/19404. |
86 | template<class _Sp, class _Tp> |
87 | struct __traitor |
88 | { |
89 | enum { __value = bool(_Sp::__value) || bool(_Tp::__value) }; |
90 | typedef typename __truth_type<__value>::__type __type; |
91 | }; |
92 | |
93 | // Compare for equality of types. |
94 | template<typename, typename> |
95 | struct __are_same |
96 | { |
97 | enum { __value = 0 }; |
98 | typedef __false_type __type; |
99 | }; |
100 | |
101 | template<typename _Tp> |
102 | struct __are_same<_Tp, _Tp> |
103 | { |
104 | enum { __value = 1 }; |
105 | typedef __true_type __type; |
106 | }; |
107 | |
108 | // Holds if the template-argument is a void type. |
109 | template<typename _Tp> |
110 | struct __is_void |
111 | { |
112 | enum { __value = 0 }; |
113 | typedef __false_type __type; |
114 | }; |
115 | |
116 | template<> |
117 | struct __is_void<void> |
118 | { |
119 | enum { __value = 1 }; |
120 | typedef __true_type __type; |
121 | }; |
122 | |
123 | // |
124 | // Integer types |
125 | // |
126 | template<typename _Tp> |
127 | struct __is_integer |
128 | { |
129 | enum { __value = 0 }; |
130 | typedef __false_type __type; |
131 | }; |
132 | |
133 | // Thirteen specializations (yes there are eleven standard integer |
134 | // types; <em>long long</em> and <em>unsigned long long</em> are |
135 | // supported as extensions). Up to four target-specific __int<N> |
136 | // types are supported as well. |
137 | template<> |
138 | struct __is_integer<bool> |
139 | { |
140 | enum { __value = 1 }; |
141 | typedef __true_type __type; |
142 | }; |
143 | |
144 | template<> |
145 | struct __is_integer<char> |
146 | { |
147 | enum { __value = 1 }; |
148 | typedef __true_type __type; |
149 | }; |
150 | |
151 | template<> |
152 | struct __is_integer<signed char> |
153 | { |
154 | enum { __value = 1 }; |
155 | typedef __true_type __type; |
156 | }; |
157 | |
158 | template<> |
159 | struct __is_integer<unsigned char> |
160 | { |
161 | enum { __value = 1 }; |
162 | typedef __true_type __type; |
163 | }; |
164 | |
165 | # ifdef __WCHAR_TYPE__ |
166 | template<> |
167 | struct __is_integer<wchar_t> |
168 | { |
169 | enum { __value = 1 }; |
170 | typedef __true_type __type; |
171 | }; |
172 | # endif |
173 | |
174 | #ifdef _GLIBCXX_USE_CHAR8_T |
175 | template<> |
176 | struct __is_integer<char8_t> |
177 | { |
178 | enum { __value = 1 }; |
179 | typedef __true_type __type; |
180 | }; |
181 | #endif |
182 | |
183 | #if __cplusplus >= 201103L |
184 | template<> |
185 | struct __is_integer<char16_t> |
186 | { |
187 | enum { __value = 1 }; |
188 | typedef __true_type __type; |
189 | }; |
190 | |
191 | template<> |
192 | struct __is_integer<char32_t> |
193 | { |
194 | enum { __value = 1 }; |
195 | typedef __true_type __type; |
196 | }; |
197 | #endif |
198 | |
199 | template<> |
200 | struct __is_integer<short> |
201 | { |
202 | enum { __value = 1 }; |
203 | typedef __true_type __type; |
204 | }; |
205 | |
206 | template<> |
207 | struct __is_integer<unsigned short> |
208 | { |
209 | enum { __value = 1 }; |
210 | typedef __true_type __type; |
211 | }; |
212 | |
213 | template<> |
214 | struct __is_integer<int> |
215 | { |
216 | enum { __value = 1 }; |
217 | typedef __true_type __type; |
218 | }; |
219 | |
220 | template<> |
221 | struct __is_integer<unsigned int> |
222 | { |
223 | enum { __value = 1 }; |
224 | typedef __true_type __type; |
225 | }; |
226 | |
227 | template<> |
228 | struct __is_integer<long> |
229 | { |
230 | enum { __value = 1 }; |
231 | typedef __true_type __type; |
232 | }; |
233 | |
234 | template<> |
235 | struct __is_integer<unsigned long> |
236 | { |
237 | enum { __value = 1 }; |
238 | typedef __true_type __type; |
239 | }; |
240 | |
241 | template<> |
242 | struct __is_integer<long long> |
243 | { |
244 | enum { __value = 1 }; |
245 | typedef __true_type __type; |
246 | }; |
247 | |
248 | template<> |
249 | struct __is_integer<unsigned long long> |
250 | { |
251 | enum { __value = 1 }; |
252 | typedef __true_type __type; |
253 | }; |
254 | |
255 | #define __INT_N(TYPE) \ |
256 | __extension__ \ |
257 | template<> \ |
258 | struct __is_integer<TYPE> \ |
259 | { \ |
260 | enum { __value = 1 }; \ |
261 | typedef __true_type __type; \ |
262 | }; \ |
263 | __extension__ \ |
264 | template<> \ |
265 | struct __is_integer<unsigned TYPE> \ |
266 | { \ |
267 | enum { __value = 1 }; \ |
268 | typedef __true_type __type; \ |
269 | }; |
270 | |
271 | #ifdef __GLIBCXX_TYPE_INT_N_0 |
272 | __INT_N(__GLIBCXX_TYPE_INT_N_0) |
273 | #endif |
274 | #ifdef __GLIBCXX_TYPE_INT_N_1 |
275 | __INT_N(__GLIBCXX_TYPE_INT_N_1) |
276 | #endif |
277 | #ifdef __GLIBCXX_TYPE_INT_N_2 |
278 | __INT_N(__GLIBCXX_TYPE_INT_N_2) |
279 | #endif |
280 | #ifdef __GLIBCXX_TYPE_INT_N_3 |
281 | __INT_N(__GLIBCXX_TYPE_INT_N_3) |
282 | #endif |
283 | |
284 | #undef __INT_N |
285 | |
286 | // |
287 | // Floating point types |
288 | // |
289 | template<typename _Tp> |
290 | struct __is_floating |
291 | { |
292 | enum { __value = 0 }; |
293 | typedef __false_type __type; |
294 | }; |
295 | |
296 | // three specializations (float, double and 'long double') |
297 | template<> |
298 | struct __is_floating<float> |
299 | { |
300 | enum { __value = 1 }; |
301 | typedef __true_type __type; |
302 | }; |
303 | |
304 | template<> |
305 | struct __is_floating<double> |
306 | { |
307 | enum { __value = 1 }; |
308 | typedef __true_type __type; |
309 | }; |
310 | |
311 | template<> |
312 | struct __is_floating<long double> |
313 | { |
314 | enum { __value = 1 }; |
315 | typedef __true_type __type; |
316 | }; |
317 | |
318 | // |
319 | // Pointer types |
320 | // |
321 | template<typename _Tp> |
322 | struct __is_pointer |
323 | { |
324 | enum { __value = 0 }; |
325 | typedef __false_type __type; |
326 | }; |
327 | |
328 | template<typename _Tp> |
329 | struct __is_pointer<_Tp*> |
330 | { |
331 | enum { __value = 1 }; |
332 | typedef __true_type __type; |
333 | }; |
334 | |
335 | // |
336 | // An arithmetic type is an integer type or a floating point type |
337 | // |
338 | template<typename _Tp> |
339 | struct __is_arithmetic |
340 | : public __traitor<__is_integer<_Tp>, __is_floating<_Tp> > |
341 | { }; |
342 | |
343 | // |
344 | // A scalar type is an arithmetic type or a pointer type |
345 | // |
346 | template<typename _Tp> |
347 | struct __is_scalar |
348 | : public __traitor<__is_arithmetic<_Tp>, __is_pointer<_Tp> > |
349 | { }; |
350 | |
351 | // |
352 | // For use in std::copy and std::find overloads for streambuf iterators. |
353 | // |
354 | template<typename _Tp> |
355 | struct __is_char |
356 | { |
357 | enum { __value = 0 }; |
358 | typedef __false_type __type; |
359 | }; |
360 | |
361 | template<> |
362 | struct __is_char<char> |
363 | { |
364 | enum { __value = 1 }; |
365 | typedef __true_type __type; |
366 | }; |
367 | |
368 | #ifdef __WCHAR_TYPE__ |
369 | template<> |
370 | struct __is_char<wchar_t> |
371 | { |
372 | enum { __value = 1 }; |
373 | typedef __true_type __type; |
374 | }; |
375 | #endif |
376 | |
377 | template<typename _Tp> |
378 | struct __is_byte |
379 | { |
380 | enum { __value = 0 }; |
381 | typedef __false_type __type; |
382 | }; |
383 | |
384 | template<> |
385 | struct __is_byte<char> |
386 | { |
387 | enum { __value = 1 }; |
388 | typedef __true_type __type; |
389 | }; |
390 | |
391 | template<> |
392 | struct __is_byte<signed char> |
393 | { |
394 | enum { __value = 1 }; |
395 | typedef __true_type __type; |
396 | }; |
397 | |
398 | template<> |
399 | struct __is_byte<unsigned char> |
400 | { |
401 | enum { __value = 1 }; |
402 | typedef __true_type __type; |
403 | }; |
404 | |
405 | #if __cplusplus >= 201703L |
406 | enum class byte : unsigned char; |
407 | |
408 | template<> |
409 | struct __is_byte<byte> |
410 | { |
411 | enum { __value = 1 }; |
412 | typedef __true_type __type; |
413 | }; |
414 | #endif // C++17 |
415 | |
416 | #ifdef _GLIBCXX_USE_CHAR8_T |
417 | template<> |
418 | struct __is_byte<char8_t> |
419 | { |
420 | enum { __value = 1 }; |
421 | typedef __true_type __type; |
422 | }; |
423 | #endif |
424 | |
425 | template<typename> struct iterator_traits; |
426 | |
427 | // A type that is safe for use with memcpy, memmove, memcmp etc. |
428 | template<typename _Tp> |
429 | struct __is_nonvolatile_trivially_copyable |
430 | { |
431 | enum { __value = __is_trivially_copyable(_Tp) }; |
432 | }; |
433 | |
434 | // Cannot use memcpy/memmove/memcmp on volatile types even if they are |
435 | // trivially copyable, so ensure __memcpyable<volatile int*, volatile int*> |
436 | // and similar will be false. |
437 | template<typename _Tp> |
438 | struct __is_nonvolatile_trivially_copyable<volatile _Tp> |
439 | { |
440 | enum { __value = 0 }; |
441 | }; |
442 | |
443 | // Whether two iterator types can be used with memcpy/memmove. |
444 | template<typename _OutputIter, typename _InputIter> |
445 | struct __memcpyable |
446 | { |
447 | enum { __value = 0 }; |
448 | }; |
449 | |
450 | template<typename _Tp> |
451 | struct __memcpyable<_Tp*, _Tp*> |
452 | : __is_nonvolatile_trivially_copyable<_Tp> |
453 | { }; |
454 | |
455 | template<typename _Tp> |
456 | struct __memcpyable<_Tp*, const _Tp*> |
457 | : __is_nonvolatile_trivially_copyable<_Tp> |
458 | { }; |
459 | |
460 | // Whether two iterator types can be used with memcmp. |
461 | // This trait only says it's well-formed to use memcmp, not that it |
462 | // gives the right answer for a given algorithm. So for example, std::equal |
463 | // needs to add additional checks that the types are integers or pointers, |
464 | // because other trivially copyable types can overload operator==. |
465 | template<typename _Iter1, typename _Iter2> |
466 | struct __memcmpable |
467 | { |
468 | enum { __value = 0 }; |
469 | }; |
470 | |
471 | // OK to use memcmp with pointers to trivially copyable types. |
472 | template<typename _Tp> |
473 | struct __memcmpable<_Tp*, _Tp*> |
474 | : __is_nonvolatile_trivially_copyable<_Tp> |
475 | { }; |
476 | |
477 | template<typename _Tp> |
478 | struct __memcmpable<const _Tp*, _Tp*> |
479 | : __is_nonvolatile_trivially_copyable<_Tp> |
480 | { }; |
481 | |
482 | template<typename _Tp> |
483 | struct __memcmpable<_Tp*, const _Tp*> |
484 | : __is_nonvolatile_trivially_copyable<_Tp> |
485 | { }; |
486 | |
487 | // Whether memcmp can be used to determine ordering for a type |
488 | // e.g. in std::lexicographical_compare or three-way comparisons. |
489 | // True for unsigned integer-like types where comparing each byte in turn |
490 | // as an unsigned char yields the right result. This is true for all |
491 | // unsigned integers on big endian targets, but only unsigned narrow |
492 | // character types (and std::byte) on little endian targets. |
493 | template<typename _Tp, bool _TreatAsBytes = |
494 | #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ |
495 | __is_integer<_Tp>::__value |
496 | #else |
497 | __is_byte<_Tp>::__value |
498 | #endif |
499 | > |
500 | struct __is_memcmp_ordered |
501 | { |
502 | static const bool __value = _Tp(-1) > _Tp(1); // is unsigned |
503 | }; |
504 | |
505 | template<typename _Tp> |
506 | struct __is_memcmp_ordered<_Tp, false> |
507 | { |
508 | static const bool __value = false; |
509 | }; |
510 | |
511 | // Whether two types can be compared using memcmp. |
512 | template<typename _Tp, typename _Up, bool = sizeof(_Tp) == sizeof(_Up)> |
513 | struct __is_memcmp_ordered_with |
514 | { |
515 | static const bool __value = __is_memcmp_ordered<_Tp>::__value |
516 | && __is_memcmp_ordered<_Up>::__value; |
517 | }; |
518 | |
519 | template<typename _Tp, typename _Up> |
520 | struct __is_memcmp_ordered_with<_Tp, _Up, false> |
521 | { |
522 | static const bool __value = false; |
523 | }; |
524 | |
525 | #if __cplusplus >= 201703L |
526 | #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ |
527 | // std::byte is not an integer, but it can be compared using memcmp. |
528 | template<> |
529 | struct __is_memcmp_ordered<std::byte, false> |
530 | { static constexpr bool __value = true; }; |
531 | #endif |
532 | |
533 | // std::byte can only be compared to itself, not to other types. |
534 | template<> |
535 | struct __is_memcmp_ordered_with<std::byte, std::byte, true> |
536 | { static constexpr bool __value = true; }; |
537 | |
538 | template<typename _Tp, bool _SameSize> |
539 | struct __is_memcmp_ordered_with<_Tp, std::byte, _SameSize> |
540 | { static constexpr bool __value = false; }; |
541 | |
542 | template<typename _Up, bool _SameSize> |
543 | struct __is_memcmp_ordered_with<std::byte, _Up, _SameSize> |
544 | { static constexpr bool __value = false; }; |
545 | #endif |
546 | |
547 | // |
548 | // Move iterator type |
549 | // |
550 | template<typename _Tp> |
551 | struct __is_move_iterator |
552 | { |
553 | enum { __value = 0 }; |
554 | typedef __false_type __type; |
555 | }; |
556 | |
557 | // Fallback implementation of the function in bits/stl_iterator.h used to |
558 | // remove the move_iterator wrapper. |
559 | template<typename _Iterator> |
560 | _GLIBCXX20_CONSTEXPR |
561 | inline _Iterator |
562 | __miter_base(_Iterator __it) |
563 | { return __it; } |
564 | |
565 | _GLIBCXX_END_NAMESPACE_VERSION |
566 | } // namespace |
567 | } // extern "C++" |
568 | |
569 | #endif //_CPP_TYPE_TRAITS_H |
570 | |