2 //===----------------------------------------------------------------------===//
4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // See https://llvm.org/LICENSE.txt for license information.
6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
8 //===----------------------------------------------------------------------===//
10 #ifndef _LIBCPP_TYPE_TRAITS
11 #define _LIBCPP_TYPE_TRAITS
20 template <class T, T v> struct integral_constant;
21 typedef integral_constant<bool, true> true_type; // C++11
22 typedef integral_constant<bool, false> false_type; // C++11
24 template <bool B> // C++14
25 using bool_constant = integral_constant<bool, B>; // C++14
26 typedef bool_constant<true> true_type; // C++14
27 typedef bool_constant<false> false_type; // C++14
30 template <bool, class T = void> struct enable_if;
31 template <bool, class T, class F> struct conditional;
33 // Primary classification traits:
34 template <class T> struct is_void;
35 template <class T> struct is_null_pointer; // C++14
36 template <class T> struct is_integral;
37 template <class T> struct is_floating_point;
38 template <class T> struct is_array;
39 template <class T> struct is_pointer;
40 template <class T> struct is_lvalue_reference;
41 template <class T> struct is_rvalue_reference;
42 template <class T> struct is_member_object_pointer;
43 template <class T> struct is_member_function_pointer;
44 template <class T> struct is_enum;
45 template <class T> struct is_union;
46 template <class T> struct is_class;
47 template <class T> struct is_function;
49 // Secondary classification traits:
50 template <class T> struct is_reference;
51 template <class T> struct is_arithmetic;
52 template <class T> struct is_fundamental;
53 template <class T> struct is_member_pointer;
54 template <class T> struct is_scoped_enum; // C++23
55 template <class T> struct is_scalar;
56 template <class T> struct is_object;
57 template <class T> struct is_compound;
59 // Const-volatile properties and transformations:
60 template <class T> struct is_const;
61 template <class T> struct is_volatile;
62 template <class T> struct remove_const;
63 template <class T> struct remove_volatile;
64 template <class T> struct remove_cv;
65 template <class T> struct add_const;
66 template <class T> struct add_volatile;
67 template <class T> struct add_cv;
69 // Reference transformations:
70 template <class T> struct remove_reference;
71 template <class T> struct add_lvalue_reference;
72 template <class T> struct add_rvalue_reference;
74 // Pointer transformations:
75 template <class T> struct remove_pointer;
76 template <class T> struct add_pointer;
78 template<class T> struct type_identity; // C++20
80 using type_identity_t = typename type_identity<T>::type; // C++20
82 // Integral properties:
83 template <class T> struct is_signed;
84 template <class T> struct is_unsigned;
85 template <class T> struct make_signed;
86 template <class T> struct make_unsigned;
88 // Array properties and transformations:
89 template <class T> struct rank;
90 template <class T, unsigned I = 0> struct extent;
91 template <class T> struct remove_extent;
92 template <class T> struct remove_all_extents;
94 template <class T> struct is_bounded_array; // C++20
95 template <class T> struct is_unbounded_array; // C++20
97 // Member introspection:
98 template <class T> struct is_pod;
99 template <class T> struct is_trivial;
100 template <class T> struct is_trivially_copyable;
101 template <class T> struct is_standard_layout;
102 template <class T> struct is_literal_type; // Deprecated in C++17; removed in C++20
103 template <class T> struct is_empty;
104 template <class T> struct is_polymorphic;
105 template <class T> struct is_abstract;
106 template <class T> struct is_final; // C++14
107 template <class T> struct is_aggregate; // C++17
109 template <class T, class... Args> struct is_constructible;
110 template <class T> struct is_default_constructible;
111 template <class T> struct is_copy_constructible;
112 template <class T> struct is_move_constructible;
113 template <class T, class U> struct is_assignable;
114 template <class T> struct is_copy_assignable;
115 template <class T> struct is_move_assignable;
116 template <class T, class U> struct is_swappable_with; // C++17
117 template <class T> struct is_swappable; // C++17
118 template <class T> struct is_destructible;
120 template <class T, class... Args> struct is_trivially_constructible;
121 template <class T> struct is_trivially_default_constructible;
122 template <class T> struct is_trivially_copy_constructible;
123 template <class T> struct is_trivially_move_constructible;
124 template <class T, class U> struct is_trivially_assignable;
125 template <class T> struct is_trivially_copy_assignable;
126 template <class T> struct is_trivially_move_assignable;
127 template <class T> struct is_trivially_destructible;
129 template <class T, class... Args> struct is_nothrow_constructible;
130 template <class T> struct is_nothrow_default_constructible;
131 template <class T> struct is_nothrow_copy_constructible;
132 template <class T> struct is_nothrow_move_constructible;
133 template <class T, class U> struct is_nothrow_assignable;
134 template <class T> struct is_nothrow_copy_assignable;
135 template <class T> struct is_nothrow_move_assignable;
136 template <class T, class U> struct is_nothrow_swappable_with; // C++17
137 template <class T> struct is_nothrow_swappable; // C++17
138 template <class T> struct is_nothrow_destructible;
140 template <class T> struct has_virtual_destructor;
142 template<class T> struct has_unique_object_representations; // C++17
144 // Relationships between types:
145 template <class T, class U> struct is_same;
146 template <class Base, class Derived> struct is_base_of;
148 template <class From, class To> struct is_convertible;
149 template <typename From, typename To> struct is_nothrow_convertible; // C++20
150 template <typename From, typename To> inline constexpr bool is_nothrow_convertible_v; // C++20
152 template <class Fn, class... ArgTypes> struct is_invocable;
153 template <class R, class Fn, class... ArgTypes> struct is_invocable_r;
155 template <class Fn, class... ArgTypes> struct is_nothrow_invocable;
156 template <class R, class Fn, class... ArgTypes> struct is_nothrow_invocable_r;
158 // Alignment properties and transformations:
159 template <class T> struct alignment_of;
160 template <size_t Len, size_t Align = most_stringent_alignment_requirement>
161 struct aligned_storage; // deprecated in C++23
162 template <size_t Len, class... Types> struct aligned_union; // deprecated in C++23
163 template <class T> struct remove_cvref; // C++20
165 template <class T> struct decay;
166 template <class... T> struct common_type;
167 template <class T> struct underlying_type;
168 template <class> class result_of; // undefined; deprecated in C++17; removed in C++20
169 template <class Fn, class... ArgTypes> class result_of<Fn(ArgTypes...)>; // deprecated in C++17; removed in C++20
170 template <class Fn, class... ArgTypes> struct invoke_result; // C++17
172 // const-volatile modifications:
174 using remove_const_t = typename remove_const<T>::type; // C++14
176 using remove_volatile_t = typename remove_volatile<T>::type; // C++14
178 using remove_cv_t = typename remove_cv<T>::type; // C++14
180 using add_const_t = typename add_const<T>::type; // C++14
182 using add_volatile_t = typename add_volatile<T>::type; // C++14
184 using add_cv_t = typename add_cv<T>::type; // C++14
186 // reference modifications:
188 using remove_reference_t = typename remove_reference<T>::type; // C++14
190 using add_lvalue_reference_t = typename add_lvalue_reference<T>::type; // C++14
192 using add_rvalue_reference_t = typename add_rvalue_reference<T>::type; // C++14
194 // sign modifications:
196 using make_signed_t = typename make_signed<T>::type; // C++14
198 using make_unsigned_t = typename make_unsigned<T>::type; // C++14
200 // array modifications:
202 using remove_extent_t = typename remove_extent<T>::type; // C++14
204 using remove_all_extents_t = typename remove_all_extents<T>::type; // C++14
207 inline constexpr bool is_bounded_array_v
208 = is_bounded_array<T>::value; // C++20
209 inline constexpr bool is_unbounded_array_v
210 = is_unbounded_array<T>::value; // C++20
212 // pointer modifications:
214 using remove_pointer_t = typename remove_pointer<T>::type; // C++14
216 using add_pointer_t = typename add_pointer<T>::type; // C++14
218 // other transformations:
219 template <size_t Len, size_t Align=default-alignment>
220 using aligned_storage_t = typename aligned_storage<Len,Align>::type; // C++14
221 template <size_t Len, class... Types>
222 using aligned_union_t = typename aligned_union<Len,Types...>::type; // C++14
224 using remove_cvref_t = typename remove_cvref<T>::type; // C++20
226 using decay_t = typename decay<T>::type; // C++14
227 template <bool b, class T=void>
228 using enable_if_t = typename enable_if<b,T>::type; // C++14
229 template <bool b, class T, class F>
230 using conditional_t = typename conditional<b,T,F>::type; // C++14
231 template <class... T>
232 using common_type_t = typename common_type<T...>::type; // C++14
234 using underlying_type_t = typename underlying_type<T>::type; // C++14
236 using result_of_t = typename result_of<T>::type; // C++14; deprecated in C++17; removed in C++20
237 template <class Fn, class... ArgTypes>
238 using invoke_result_t = typename invoke_result<Fn, ArgTypes...>::type; // C++17
241 using void_t = void; // C++17
243 // See C++14 20.10.4.1, primary type categories
244 template <class T> inline constexpr bool is_void_v
245 = is_void<T>::value; // C++17
246 template <class T> inline constexpr bool is_null_pointer_v
247 = is_null_pointer<T>::value; // C++17
248 template <class T> inline constexpr bool is_integral_v
249 = is_integral<T>::value; // C++17
250 template <class T> inline constexpr bool is_floating_point_v
251 = is_floating_point<T>::value; // C++17
252 template <class T> inline constexpr bool is_array_v
253 = is_array<T>::value; // C++17
254 template <class T> inline constexpr bool is_pointer_v
255 = is_pointer<T>::value; // C++17
256 template <class T> inline constexpr bool is_lvalue_reference_v
257 = is_lvalue_reference<T>::value; // C++17
258 template <class T> inline constexpr bool is_rvalue_reference_v
259 = is_rvalue_reference<T>::value; // C++17
260 template <class T> inline constexpr bool is_member_object_pointer_v
261 = is_member_object_pointer<T>::value; // C++17
262 template <class T> inline constexpr bool is_member_function_pointer_v
263 = is_member_function_pointer<T>::value; // C++17
264 template <class T> inline constexpr bool is_enum_v
265 = is_enum<T>::value; // C++17
266 template <class T> inline constexpr bool is_union_v
267 = is_union<T>::value; // C++17
268 template <class T> inline constexpr bool is_class_v
269 = is_class<T>::value; // C++17
270 template <class T> inline constexpr bool is_function_v
271 = is_function<T>::value; // C++17
273 // See C++14 20.10.4.2, composite type categories
274 template <class T> inline constexpr bool is_reference_v
275 = is_reference<T>::value; // C++17
276 template <class T> inline constexpr bool is_arithmetic_v
277 = is_arithmetic<T>::value; // C++17
278 template <class T> inline constexpr bool is_fundamental_v
279 = is_fundamental<T>::value; // C++17
280 template <class T> inline constexpr bool is_object_v
281 = is_object<T>::value; // C++17
282 template <class T> inline constexpr bool is_scalar_v
283 = is_scalar<T>::value; // C++17
284 template <class T> inline constexpr bool is_compound_v
285 = is_compound<T>::value; // C++17
286 template <class T> inline constexpr bool is_member_pointer_v
287 = is_member_pointer<T>::value; // C++17
288 template <class T> inline constexpr bool is_scoped_enum_v
289 = is_scoped_enum<T>::value; // C++23
291 // See C++14 20.10.4.3, type properties
292 template <class T> inline constexpr bool is_const_v
293 = is_const<T>::value; // C++17
294 template <class T> inline constexpr bool is_volatile_v
295 = is_volatile<T>::value; // C++17
296 template <class T> inline constexpr bool is_trivial_v
297 = is_trivial<T>::value; // C++17
298 template <class T> inline constexpr bool is_trivially_copyable_v
299 = is_trivially_copyable<T>::value; // C++17
300 template <class T> inline constexpr bool is_standard_layout_v
301 = is_standard_layout<T>::value; // C++17
302 template <class T> inline constexpr bool is_pod_v
303 = is_pod<T>::value; // C++17
304 template <class T> inline constexpr bool is_literal_type_v
305 = is_literal_type<T>::value; // C++17; deprecated in C++17; removed in C++20
306 template <class T> inline constexpr bool is_empty_v
307 = is_empty<T>::value; // C++17
308 template <class T> inline constexpr bool is_polymorphic_v
309 = is_polymorphic<T>::value; // C++17
310 template <class T> inline constexpr bool is_abstract_v
311 = is_abstract<T>::value; // C++17
312 template <class T> inline constexpr bool is_final_v
313 = is_final<T>::value; // C++17
314 template <class T> inline constexpr bool is_aggregate_v
315 = is_aggregate<T>::value; // C++17
316 template <class T> inline constexpr bool is_signed_v
317 = is_signed<T>::value; // C++17
318 template <class T> inline constexpr bool is_unsigned_v
319 = is_unsigned<T>::value; // C++17
320 template <class T, class... Args> inline constexpr bool is_constructible_v
321 = is_constructible<T, Args...>::value; // C++17
322 template <class T> inline constexpr bool is_default_constructible_v
323 = is_default_constructible<T>::value; // C++17
324 template <class T> inline constexpr bool is_copy_constructible_v
325 = is_copy_constructible<T>::value; // C++17
326 template <class T> inline constexpr bool is_move_constructible_v
327 = is_move_constructible<T>::value; // C++17
328 template <class T, class U> inline constexpr bool is_assignable_v
329 = is_assignable<T, U>::value; // C++17
330 template <class T> inline constexpr bool is_copy_assignable_v
331 = is_copy_assignable<T>::value; // C++17
332 template <class T> inline constexpr bool is_move_assignable_v
333 = is_move_assignable<T>::value; // C++17
334 template <class T, class U> inline constexpr bool is_swappable_with_v
335 = is_swappable_with<T, U>::value; // C++17
336 template <class T> inline constexpr bool is_swappable_v
337 = is_swappable<T>::value; // C++17
338 template <class T> inline constexpr bool is_destructible_v
339 = is_destructible<T>::value; // C++17
340 template <class T, class... Args> inline constexpr bool is_trivially_constructible_v
341 = is_trivially_constructible<T, Args...>::value; // C++17
342 template <class T> inline constexpr bool is_trivially_default_constructible_v
343 = is_trivially_default_constructible<T>::value; // C++17
344 template <class T> inline constexpr bool is_trivially_copy_constructible_v
345 = is_trivially_copy_constructible<T>::value; // C++17
346 template <class T> inline constexpr bool is_trivially_move_constructible_v
347 = is_trivially_move_constructible<T>::value; // C++17
348 template <class T, class U> inline constexpr bool is_trivially_assignable_v
349 = is_trivially_assignable<T, U>::value; // C++17
350 template <class T> inline constexpr bool is_trivially_copy_assignable_v
351 = is_trivially_copy_assignable<T>::value; // C++17
352 template <class T> inline constexpr bool is_trivially_move_assignable_v
353 = is_trivially_move_assignable<T>::value; // C++17
354 template <class T> inline constexpr bool is_trivially_destructible_v
355 = is_trivially_destructible<T>::value; // C++17
356 template <class T, class... Args> inline constexpr bool is_nothrow_constructible_v
357 = is_nothrow_constructible<T, Args...>::value; // C++17
358 template <class T> inline constexpr bool is_nothrow_default_constructible_v
359 = is_nothrow_default_constructible<T>::value; // C++17
360 template <class T> inline constexpr bool is_nothrow_copy_constructible_v
361 = is_nothrow_copy_constructible<T>::value; // C++17
362 template <class T> inline constexpr bool is_nothrow_move_constructible_v
363 = is_nothrow_move_constructible<T>::value; // C++17
364 template <class T, class U> inline constexpr bool is_nothrow_assignable_v
365 = is_nothrow_assignable<T, U>::value; // C++17
366 template <class T> inline constexpr bool is_nothrow_copy_assignable_v
367 = is_nothrow_copy_assignable<T>::value; // C++17
368 template <class T> inline constexpr bool is_nothrow_move_assignable_v
369 = is_nothrow_move_assignable<T>::value; // C++17
370 template <class T, class U> inline constexpr bool is_nothrow_swappable_with_v
371 = is_nothrow_swappable_with<T, U>::value; // C++17
372 template <class T> inline constexpr bool is_nothrow_swappable_v
373 = is_nothrow_swappable<T>::value; // C++17
374 template <class T> inline constexpr bool is_nothrow_destructible_v
375 = is_nothrow_destructible<T>::value; // C++17
376 template <class T> inline constexpr bool has_virtual_destructor_v
377 = has_virtual_destructor<T>::value; // C++17
378 template<class T> inline constexpr bool has_unique_object_representations_v // C++17
379 = has_unique_object_representations<T>::value;
381 // See C++14 20.10.5, type property queries
382 template <class T> inline constexpr size_t alignment_of_v
383 = alignment_of<T>::value; // C++17
384 template <class T> inline constexpr size_t rank_v
385 = rank<T>::value; // C++17
386 template <class T, unsigned I = 0> inline constexpr size_t extent_v
387 = extent<T, I>::value; // C++17
389 // See C++14 20.10.6, type relations
390 template <class T, class U> inline constexpr bool is_same_v
391 = is_same<T, U>::value; // C++17
392 template <class Base, class Derived> inline constexpr bool is_base_of_v
393 = is_base_of<Base, Derived>::value; // C++17
394 template <class From, class To> inline constexpr bool is_convertible_v
395 = is_convertible<From, To>::value; // C++17
396 template <class Fn, class... ArgTypes> inline constexpr bool is_invocable_v
397 = is_invocable<Fn, ArgTypes...>::value; // C++17
398 template <class R, class Fn, class... ArgTypes> inline constexpr bool is_invocable_r_v
399 = is_invocable_r<R, Fn, ArgTypes...>::value; // C++17
400 template <class Fn, class... ArgTypes> inline constexpr bool is_nothrow_invocable_v
401 = is_nothrow_invocable<Fn, ArgTypes...>::value; // C++17
402 template <class R, class Fn, class... ArgTypes> inline constexpr bool is_nothrow_invocable_r_v
403 = is_nothrow_invocable_r<R, Fn, ArgTypes...>::value; // C++17
405 // [meta.logical], logical operator traits:
406 template<class... B> struct conjunction; // C++17
408 inline constexpr bool conjunction_v = conjunction<B...>::value; // C++17
409 template<class... B> struct disjunction; // C++17
411 inline constexpr bool disjunction_v = disjunction<B...>::value; // C++17
412 template<class B> struct negation; // C++17
414 inline constexpr bool negation_v = negation<B>::value; // C++17
419 #include <__assert> // all public C++ headers provide the assertion handler
421 #include <__fwd/hash.h> // This is https://llvm.org/PR56938
422 #include <__type_traits/add_const.h>
423 #include <__type_traits/add_cv.h>
424 #include <__type_traits/add_lvalue_reference.h>
425 #include <__type_traits/add_pointer.h>
426 #include <__type_traits/add_rvalue_reference.h>
427 #include <__type_traits/add_volatile.h>
428 #include <__type_traits/aligned_storage.h>
429 #include <__type_traits/aligned_union.h>
430 #include <__type_traits/alignment_of.h>
431 #include <__type_traits/apply_cv.h>
432 #include <__type_traits/can_extract_key.h>
433 #include <__type_traits/common_reference.h>
434 #include <__type_traits/common_type.h>
435 #include <__type_traits/conditional.h>
436 #include <__type_traits/conjunction.h>
437 #include <__type_traits/decay.h>
438 #include <__type_traits/dependent_type.h>
439 #include <__type_traits/disjunction.h>
440 #include <__type_traits/enable_if.h>
441 #include <__type_traits/extent.h>
442 #include <__type_traits/has_unique_object_representation.h>
443 #include <__type_traits/has_virtual_destructor.h>
444 #include <__type_traits/integral_constant.h>
445 #include <__type_traits/invoke.h>
446 #include <__type_traits/is_abstract.h>
447 #include <__type_traits/is_aggregate.h>
448 #include <__type_traits/is_arithmetic.h>
449 #include <__type_traits/is_array.h>
450 #include <__type_traits/is_assignable.h>
451 #include <__type_traits/is_base_of.h>
452 #include <__type_traits/is_bounded_array.h>
453 #include <__type_traits/is_callable.h>
454 #include <__type_traits/is_char_like_type.h>
455 #include <__type_traits/is_class.h>
456 #include <__type_traits/is_compound.h>
457 #include <__type_traits/is_const.h>
458 #include <__type_traits/is_constant_evaluated.h>
459 #include <__type_traits/is_constructible.h>
460 #include <__type_traits/is_convertible.h>
461 #include <__type_traits/is_copy_assignable.h>
462 #include <__type_traits/is_copy_constructible.h>
463 #include <__type_traits/is_default_constructible.h>
464 #include <__type_traits/is_destructible.h>
465 #include <__type_traits/is_empty.h>
466 #include <__type_traits/is_enum.h>
467 #include <__type_traits/is_final.h>
468 #include <__type_traits/is_floating_point.h>
469 #include <__type_traits/is_function.h>
470 #include <__type_traits/is_fundamental.h>
471 #include <__type_traits/is_implicitly_default_constructible.h>
472 #include <__type_traits/is_integral.h>
473 #include <__type_traits/is_literal_type.h>
474 #include <__type_traits/is_member_function_pointer.h>
475 #include <__type_traits/is_member_object_pointer.h>
476 #include <__type_traits/is_member_pointer.h>
477 #include <__type_traits/is_move_assignable.h>
478 #include <__type_traits/is_move_constructible.h>
479 #include <__type_traits/is_nothrow_assignable.h>
480 #include <__type_traits/is_nothrow_constructible.h>
481 #include <__type_traits/is_nothrow_convertible.h>
482 #include <__type_traits/is_nothrow_copy_assignable.h>
483 #include <__type_traits/is_nothrow_copy_constructible.h>
484 #include <__type_traits/is_nothrow_default_constructible.h>
485 #include <__type_traits/is_nothrow_destructible.h>
486 #include <__type_traits/is_nothrow_move_assignable.h>
487 #include <__type_traits/is_nothrow_move_constructible.h>
488 #include <__type_traits/is_null_pointer.h>
489 #include <__type_traits/is_object.h>
490 #include <__type_traits/is_pod.h>
491 #include <__type_traits/is_pointer.h>
492 #include <__type_traits/is_polymorphic.h>
493 #include <__type_traits/is_reference.h>
494 #include <__type_traits/is_reference_wrapper.h>
495 #include <__type_traits/is_referenceable.h>
496 #include <__type_traits/is_same.h>
497 #include <__type_traits/is_scalar.h>
498 #include <__type_traits/is_scoped_enum.h>
499 #include <__type_traits/is_signed.h>
500 #include <__type_traits/is_specialization.h>
501 #include <__type_traits/is_standard_layout.h>
502 #include <__type_traits/is_swappable.h>
503 #include <__type_traits/is_trivial.h>
504 #include <__type_traits/is_trivially_assignable.h>
505 #include <__type_traits/is_trivially_constructible.h>
506 #include <__type_traits/is_trivially_copy_assignable.h>
507 #include <__type_traits/is_trivially_copy_constructible.h>
508 #include <__type_traits/is_trivially_copyable.h>
509 #include <__type_traits/is_trivially_default_constructible.h>
510 #include <__type_traits/is_trivially_destructible.h>
511 #include <__type_traits/is_trivially_move_assignable.h>
512 #include <__type_traits/is_trivially_move_constructible.h>
513 #include <__type_traits/is_unbounded_array.h>
514 #include <__type_traits/is_union.h>
515 #include <__type_traits/is_unsigned.h>
516 #include <__type_traits/is_void.h>
517 #include <__type_traits/is_volatile.h>
518 #include <__type_traits/make_const_lvalue_ref.h>
519 #include <__type_traits/make_signed.h>
520 #include <__type_traits/make_unsigned.h>
521 #include <__type_traits/maybe_const.h>
522 #include <__type_traits/negation.h>
523 #include <__type_traits/rank.h>
524 #include <__type_traits/remove_all_extents.h>
525 #include <__type_traits/remove_const.h>
526 #include <__type_traits/remove_const_ref.h>
527 #include <__type_traits/remove_cv.h>
528 #include <__type_traits/remove_extent.h>
529 #include <__type_traits/remove_pointer.h>
530 #include <__type_traits/remove_reference.h>
531 #include <__type_traits/remove_volatile.h>
532 #include <__type_traits/result_of.h>
533 #include <__type_traits/type_identity.h>
534 #include <__type_traits/underlying_type.h>
535 #include <__type_traits/unwrap_ref.h>
536 #include <__type_traits/void_t.h>
537 #include <__utility/declval.h>
542 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
543 # pragma GCC system_header
546 #endif // _LIBCPP_TYPE_TRAITS