1 | // The -*- C++ -*- type traits classes for internal use in libstdc++ |
2 | |
3 | // Copyright (C) 2000-2024 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 | #ifdef __STDCPP_FLOAT16_T__ |
319 | template<> |
320 | struct __is_floating<_Float16> |
321 | { |
322 | enum { __value = 1 }; |
323 | typedef __true_type __type; |
324 | }; |
325 | #endif |
326 | |
327 | #ifdef __STDCPP_FLOAT32_T__ |
328 | template<> |
329 | struct __is_floating<_Float32> |
330 | { |
331 | enum { __value = 1 }; |
332 | typedef __true_type __type; |
333 | }; |
334 | #endif |
335 | |
336 | #ifdef __STDCPP_FLOAT64_T__ |
337 | template<> |
338 | struct __is_floating<_Float64> |
339 | { |
340 | enum { __value = 1 }; |
341 | typedef __true_type __type; |
342 | }; |
343 | #endif |
344 | |
345 | #ifdef __STDCPP_FLOAT128_T__ |
346 | template<> |
347 | struct __is_floating<_Float128> |
348 | { |
349 | enum { __value = 1 }; |
350 | typedef __true_type __type; |
351 | }; |
352 | #endif |
353 | |
354 | #ifdef __STDCPP_BFLOAT16_T__ |
355 | template<> |
356 | struct __is_floating<__gnu_cxx::__bfloat16_t> |
357 | { |
358 | enum { __value = 1 }; |
359 | typedef __true_type __type; |
360 | }; |
361 | #endif |
362 | |
363 | // |
364 | // Pointer types |
365 | // |
366 | template<typename _Tp> |
367 | struct __is_pointer |
368 | { |
369 | enum { __value = 0 }; |
370 | typedef __false_type __type; |
371 | }; |
372 | |
373 | template<typename _Tp> |
374 | struct __is_pointer<_Tp*> |
375 | { |
376 | enum { __value = 1 }; |
377 | typedef __true_type __type; |
378 | }; |
379 | |
380 | // |
381 | // An arithmetic type is an integer type or a floating point type |
382 | // |
383 | template<typename _Tp> |
384 | struct __is_arithmetic |
385 | : public __traitor<__is_integer<_Tp>, __is_floating<_Tp> > |
386 | { }; |
387 | |
388 | // |
389 | // A scalar type is an arithmetic type or a pointer type |
390 | // |
391 | template<typename _Tp> |
392 | struct __is_scalar |
393 | : public __traitor<__is_arithmetic<_Tp>, __is_pointer<_Tp> > |
394 | { }; |
395 | |
396 | // |
397 | // For use in std::copy and std::find overloads for streambuf iterators. |
398 | // |
399 | template<typename _Tp> |
400 | struct __is_char |
401 | { |
402 | enum { __value = 0 }; |
403 | typedef __false_type __type; |
404 | }; |
405 | |
406 | template<> |
407 | struct __is_char<char> |
408 | { |
409 | enum { __value = 1 }; |
410 | typedef __true_type __type; |
411 | }; |
412 | |
413 | #ifdef __WCHAR_TYPE__ |
414 | template<> |
415 | struct __is_char<wchar_t> |
416 | { |
417 | enum { __value = 1 }; |
418 | typedef __true_type __type; |
419 | }; |
420 | #endif |
421 | |
422 | template<typename _Tp> |
423 | struct __is_byte |
424 | { |
425 | enum { __value = 0 }; |
426 | typedef __false_type __type; |
427 | }; |
428 | |
429 | template<> |
430 | struct __is_byte<char> |
431 | { |
432 | enum { __value = 1 }; |
433 | typedef __true_type __type; |
434 | }; |
435 | |
436 | template<> |
437 | struct __is_byte<signed char> |
438 | { |
439 | enum { __value = 1 }; |
440 | typedef __true_type __type; |
441 | }; |
442 | |
443 | template<> |
444 | struct __is_byte<unsigned char> |
445 | { |
446 | enum { __value = 1 }; |
447 | typedef __true_type __type; |
448 | }; |
449 | |
450 | #if __cplusplus >= 201703L |
451 | enum class byte : unsigned char; |
452 | |
453 | template<> |
454 | struct __is_byte<byte> |
455 | { |
456 | enum { __value = 1 }; |
457 | typedef __true_type __type; |
458 | }; |
459 | #endif // C++17 |
460 | |
461 | #ifdef _GLIBCXX_USE_CHAR8_T |
462 | template<> |
463 | struct __is_byte<char8_t> |
464 | { |
465 | enum { __value = 1 }; |
466 | typedef __true_type __type; |
467 | }; |
468 | #endif |
469 | |
470 | template<typename> struct iterator_traits; |
471 | |
472 | // A type that is safe for use with memcpy, memmove, memcmp etc. |
473 | template<typename _Tp> |
474 | struct __is_nonvolatile_trivially_copyable |
475 | { |
476 | enum { __value = __is_trivially_copyable(_Tp) }; |
477 | }; |
478 | |
479 | // Cannot use memcpy/memmove/memcmp on volatile types even if they are |
480 | // trivially copyable, so ensure __memcpyable<volatile int*, volatile int*> |
481 | // and similar will be false. |
482 | template<typename _Tp> |
483 | struct __is_nonvolatile_trivially_copyable<volatile _Tp> |
484 | { |
485 | enum { __value = 0 }; |
486 | }; |
487 | |
488 | // Whether two iterator types can be used with memcpy/memmove. |
489 | template<typename _OutputIter, typename _InputIter> |
490 | struct __memcpyable |
491 | { |
492 | enum { __value = 0 }; |
493 | }; |
494 | |
495 | template<typename _Tp> |
496 | struct __memcpyable<_Tp*, _Tp*> |
497 | : __is_nonvolatile_trivially_copyable<_Tp> |
498 | { }; |
499 | |
500 | template<typename _Tp> |
501 | struct __memcpyable<_Tp*, const _Tp*> |
502 | : __is_nonvolatile_trivially_copyable<_Tp> |
503 | { }; |
504 | |
505 | // Whether two iterator types can be used with memcmp. |
506 | // This trait only says it's well-formed to use memcmp, not that it |
507 | // gives the right answer for a given algorithm. So for example, std::equal |
508 | // needs to add additional checks that the types are integers or pointers, |
509 | // because other trivially copyable types can overload operator==. |
510 | template<typename _Iter1, typename _Iter2> |
511 | struct __memcmpable |
512 | { |
513 | enum { __value = 0 }; |
514 | }; |
515 | |
516 | // OK to use memcmp with pointers to trivially copyable types. |
517 | template<typename _Tp> |
518 | struct __memcmpable<_Tp*, _Tp*> |
519 | : __is_nonvolatile_trivially_copyable<_Tp> |
520 | { }; |
521 | |
522 | template<typename _Tp> |
523 | struct __memcmpable<const _Tp*, _Tp*> |
524 | : __is_nonvolatile_trivially_copyable<_Tp> |
525 | { }; |
526 | |
527 | template<typename _Tp> |
528 | struct __memcmpable<_Tp*, const _Tp*> |
529 | : __is_nonvolatile_trivially_copyable<_Tp> |
530 | { }; |
531 | |
532 | // Whether memcmp can be used to determine ordering for a type |
533 | // e.g. in std::lexicographical_compare or three-way comparisons. |
534 | // True for unsigned integer-like types where comparing each byte in turn |
535 | // as an unsigned char yields the right result. This is true for all |
536 | // unsigned integers on big endian targets, but only unsigned narrow |
537 | // character types (and std::byte) on little endian targets. |
538 | template<typename _Tp, bool _TreatAsBytes = |
539 | #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ |
540 | __is_integer<_Tp>::__value |
541 | #else |
542 | __is_byte<_Tp>::__value |
543 | #endif |
544 | > |
545 | struct __is_memcmp_ordered |
546 | { |
547 | static const bool __value = _Tp(-1) > _Tp(1); // is unsigned |
548 | }; |
549 | |
550 | template<typename _Tp> |
551 | struct __is_memcmp_ordered<_Tp, false> |
552 | { |
553 | static const bool __value = false; |
554 | }; |
555 | |
556 | // Whether two types can be compared using memcmp. |
557 | template<typename _Tp, typename _Up, bool = sizeof(_Tp) == sizeof(_Up)> |
558 | struct __is_memcmp_ordered_with |
559 | { |
560 | static const bool __value = __is_memcmp_ordered<_Tp>::__value |
561 | && __is_memcmp_ordered<_Up>::__value; |
562 | }; |
563 | |
564 | template<typename _Tp, typename _Up> |
565 | struct __is_memcmp_ordered_with<_Tp, _Up, false> |
566 | { |
567 | static const bool __value = false; |
568 | }; |
569 | |
570 | #if __cplusplus >= 201703L |
571 | #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ |
572 | // std::byte is not an integer, but it can be compared using memcmp. |
573 | template<> |
574 | struct __is_memcmp_ordered<std::byte, false> |
575 | { static constexpr bool __value = true; }; |
576 | #endif |
577 | |
578 | // std::byte can only be compared to itself, not to other types. |
579 | template<> |
580 | struct __is_memcmp_ordered_with<std::byte, std::byte, true> |
581 | { static constexpr bool __value = true; }; |
582 | |
583 | template<typename _Tp, bool _SameSize> |
584 | struct __is_memcmp_ordered_with<_Tp, std::byte, _SameSize> |
585 | { static constexpr bool __value = false; }; |
586 | |
587 | template<typename _Up, bool _SameSize> |
588 | struct __is_memcmp_ordered_with<std::byte, _Up, _SameSize> |
589 | { static constexpr bool __value = false; }; |
590 | #endif |
591 | |
592 | // |
593 | // Move iterator type |
594 | // |
595 | template<typename _Tp> |
596 | struct __is_move_iterator |
597 | { |
598 | enum { __value = 0 }; |
599 | typedef __false_type __type; |
600 | }; |
601 | |
602 | // Fallback implementation of the function in bits/stl_iterator.h used to |
603 | // remove the move_iterator wrapper. |
604 | template<typename _Iterator> |
605 | _GLIBCXX20_CONSTEXPR |
606 | inline _Iterator |
607 | __miter_base(_Iterator __it) |
608 | { return __it; } |
609 | |
610 | _GLIBCXX_END_NAMESPACE_VERSION |
611 | } // namespace |
612 | } // extern "C++" |
613 | |
614 | #endif //_CPP_TYPE_TRAITS_H |
615 | |