1 // C++0x type_traits -*- C++ -*-
3 // Copyright (C) 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
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)
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.
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.
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/>.
25 /** @file include/type_traits
26 * This is a Standard C++ Library header.
29 #ifndef _GLIBCXX_TYPE_TRAITS
30 #define _GLIBCXX_TYPE_TRAITS 1
32 #pragma GCC system_header
34 #ifndef __GXX_EXPERIMENTAL_CXX0X__
35 # include <bits/c++0x_warning.h>
38 #if defined(_GLIBCXX_INCLUDE_AS_TR1)
39 # error C++0x header cannot be included from TR1 header
44 #if defined(_GLIBCXX_INCLUDE_AS_CXX0X)
45 # include <tr1_impl/type_traits>
47 # define _GLIBCXX_INCLUDE_AS_CXX0X
48 # define _GLIBCXX_BEGIN_NAMESPACE_TR1
49 # define _GLIBCXX_END_NAMESPACE_TR1
51 # include <tr1_impl/type_traits>
53 # undef _GLIBCXX_END_NAMESPACE_TR1
54 # undef _GLIBCXX_BEGIN_NAMESPACE_TR1
55 # undef _GLIBCXX_INCLUDE_AS_CXX0X
61 * @addtogroup metaprogramming
65 // Primary classification traits.
67 /// is_lvalue_reference
69 struct is_lvalue_reference
70 : public false_type { };
72 template<typename _Tp>
73 struct is_lvalue_reference<_Tp&>
74 : public true_type { };
76 /// is_rvalue_reference
78 struct is_rvalue_reference
79 : public false_type { };
81 template<typename _Tp>
82 struct is_rvalue_reference<_Tp&&>
83 : public true_type { };
85 // Secondary classification traits.
88 template<typename _Tp>
90 : public integral_constant<bool, (is_lvalue_reference<_Tp>::value
91 || is_rvalue_reference<_Tp>::value)>
94 // Reference transformations.
97 template<typename _Tp>
98 struct remove_reference
99 { typedef _Tp type; };
101 template<typename _Tp>
102 struct remove_reference<_Tp&>
103 { typedef _Tp type; };
105 template<typename _Tp>
106 struct remove_reference<_Tp&&>
107 { typedef _Tp type; };
109 template<typename _Tp,
110 bool = !is_reference<_Tp>::value && !is_void<_Tp>::value,
111 bool = is_rvalue_reference<_Tp>::value>
112 struct __add_lvalue_reference_helper
113 { typedef _Tp type; };
115 template<typename _Tp>
116 struct __add_lvalue_reference_helper<_Tp, true, false>
117 { typedef _Tp& type; };
119 template<typename _Tp>
120 struct __add_lvalue_reference_helper<_Tp, false, true>
121 { typedef typename remove_reference<_Tp>::type& type; };
123 /// add_lvalue_reference
124 template<typename _Tp>
125 struct add_lvalue_reference
126 : public __add_lvalue_reference_helper<_Tp>
129 template<typename _Tp,
130 bool = !is_reference<_Tp>::value && !is_void<_Tp>::value>
131 struct __add_rvalue_reference_helper
132 { typedef _Tp type; };
134 template<typename _Tp>
135 struct __add_rvalue_reference_helper<_Tp, true>
136 { typedef _Tp&& type; };
138 /// add_rvalue_reference
139 template<typename _Tp>
140 struct add_rvalue_reference
141 : public __add_rvalue_reference_helper<_Tp>
144 // Scalar properties and transformations.
146 template<typename _Tp,
147 bool = is_integral<_Tp>::value,
148 bool = is_floating_point<_Tp>::value>
149 struct __is_signed_helper
150 : public false_type { };
152 template<typename _Tp>
153 struct __is_signed_helper<_Tp, false, true>
154 : public true_type { };
156 template<typename _Tp>
157 struct __is_signed_helper<_Tp, true, false>
158 : public integral_constant<bool, static_cast<bool>(_Tp(-1) < _Tp(0))>
162 template<typename _Tp>
164 : public integral_constant<bool, __is_signed_helper<_Tp>::value>
168 template<typename _Tp>
170 : public integral_constant<bool, (is_arithmetic<_Tp>::value
171 && !is_signed<_Tp>::value)>
174 // Member introspection.
177 template<typename _Tp>
179 : public integral_constant<bool, __is_trivial(_Tp)>
182 /// is_standard_layout
183 template<typename _Tp>
184 struct is_standard_layout
185 : public integral_constant<bool, __is_standard_layout(_Tp)>
189 // Could use is_standard_layout && is_trivial instead of the builtin.
190 template<typename _Tp>
192 : public integral_constant<bool, __is_pod(_Tp)>
195 template<typename _Tp>
196 typename add_rvalue_reference<_Tp>::type declval();
198 template<typename _Tp, typename... _Args>
199 class __is_constructible_helper
200 : public __sfinae_types
202 template<typename _Tp1, typename... _Args1>
203 static decltype(_Tp1(declval<_Args1>()...), __one()) __test(int);
205 template<typename, typename...>
206 static __two __test(...);
209 static const bool __value = sizeof(__test<_Tp, _Args...>(0)) == 1;
212 template<typename _Tp, typename _Arg>
213 class __is_constructible_helper<_Tp, _Arg>
214 : public __sfinae_types
216 template<typename _Tp1, typename _Arg1>
217 static decltype(static_cast<_Tp1>(declval<_Arg1>()), __one())
220 template<typename, typename>
221 static __two __test(...);
224 static const bool __value = sizeof(__test<_Tp, _Arg>(0)) == 1;
229 // The C++0x specifications require front-end support, see N2255.
230 template<typename _Tp, typename... _Args>
231 struct is_constructible
232 : public integral_constant<bool,
233 __is_constructible_helper<_Tp,
237 /// has_trivial_default_constructor
238 template<typename _Tp>
239 struct has_trivial_default_constructor
240 : public integral_constant<bool, __has_trivial_constructor(_Tp)>
243 /// has_trivial_copy_constructor
244 template<typename _Tp>
245 struct has_trivial_copy_constructor
246 : public integral_constant<bool, __has_trivial_copy(_Tp)>
249 /// has_trivial_assign
250 template<typename _Tp>
251 struct has_trivial_assign
252 : public integral_constant<bool, __has_trivial_assign(_Tp)>
255 /// has_trivial_destructor
256 template<typename _Tp>
257 struct has_trivial_destructor
258 : public integral_constant<bool, __has_trivial_destructor(_Tp)>
261 /// has_nothrow_default_constructor
262 template<typename _Tp>
263 struct has_nothrow_default_constructor
264 : public integral_constant<bool, __has_nothrow_constructor(_Tp)>
267 /// has_nothrow_copy_constructor
268 template<typename _Tp>
269 struct has_nothrow_copy_constructor
270 : public integral_constant<bool, __has_nothrow_copy(_Tp)>
273 /// has_nothrow_assign
274 template<typename _Tp>
275 struct has_nothrow_assign
276 : public integral_constant<bool, __has_nothrow_assign(_Tp)>
279 // Relationships between types.
282 template<typename _Base, typename _Derived>
284 : public integral_constant<bool, __is_base_of(_Base, _Derived)>
287 template<typename _From, typename _To,
288 bool = (is_void<_From>::value || is_void<_To>::value
289 || is_function<_To>::value || is_array<_To>::value)>
290 struct __is_convertible_helper
291 { static const bool __value = (is_void<_From>::value
292 && is_void<_To>::value); };
294 template<typename _From, typename _To>
295 class __is_convertible_helper<_From, _To, false>
296 : public __sfinae_types
298 static __one __test(_To);
299 static __two __test(...);
302 static const bool __value = sizeof(__test(declval<_From>())) == 1;
307 // The C++0x specifications require front-end support, see N2255.
308 template<typename _From, typename _To>
309 struct is_convertible
310 : public integral_constant<bool,
311 __is_convertible_helper<_From, _To>::__value>
314 /// is_explicitly_convertible
315 template<typename _From, typename _To>
316 struct is_explicitly_convertible
317 : public is_constructible<_To, _From>
320 template<std::size_t _Len>
321 struct __aligned_storage_msa
325 unsigned char __data[_Len];
326 struct __attribute__((__aligned__)) { } __align;
331 * @brief Alignment type.
333 * The value of _Align is a default-alignment which shall be the
334 * most stringent alignment requirement for any C++ object type
335 * whose size is no greater than _Len (3.9). The member typedef
336 * type shall be a POD type suitable for use as uninitialized
337 * storage for any object whose size is at most _Len and whose
338 * alignment is a divisor of _Align.
340 template<std::size_t _Len, std::size_t _Align =
341 __alignof__(typename __aligned_storage_msa<_Len>::__type)>
342 struct aligned_storage
346 unsigned char __data[_Len];
347 struct __attribute__((__aligned__((_Align)))) { } __align;
352 // Define a nested type if some predicate holds.
355 template<bool, typename _Tp = void>
359 // Partial specialization for true.
360 template<typename _Tp>
361 struct enable_if<true, _Tp>
362 { typedef _Tp type; };
365 // A conditional expression, but for types. If true, first, if false, second.
368 template<bool _Cond, typename _Iftrue, typename _Iffalse>
370 { typedef _Iftrue type; };
372 // Partial specialization for false.
373 template<typename _Iftrue, typename _Iffalse>
374 struct conditional<false, _Iftrue, _Iffalse>
375 { typedef _Iffalse type; };
378 // Decay trait for arrays and functions, used for perfect forwarding
379 // in make_pair, make_tuple, etc.
380 template<typename _Up,
381 bool _IsArray = is_array<_Up>::value,
382 bool _IsFunction = is_function<_Up>::value>
383 struct __decay_selector;
386 template<typename _Up>
387 struct __decay_selector<_Up, false, false>
388 { typedef typename remove_cv<_Up>::type __type; };
390 template<typename _Up>
391 struct __decay_selector<_Up, true, false>
392 { typedef typename remove_extent<_Up>::type* __type; };
394 template<typename _Up>
395 struct __decay_selector<_Up, false, true>
396 { typedef typename add_pointer<_Up>::type __type; };
399 template<typename _Tp>
402 typedef typename remove_reference<_Tp>::type __remove_type;
405 typedef typename __decay_selector<__remove_type>::__type type;
408 template<typename _Tp>
409 class reference_wrapper;
411 // Helper which adds a reference to a type when given a reference_wrapper
412 template<typename _Tp>
413 struct __strip_reference_wrapper
418 template<typename _Tp>
419 struct __strip_reference_wrapper<reference_wrapper<_Tp> >
424 template<typename _Tp>
425 struct __strip_reference_wrapper<const reference_wrapper<_Tp> >
430 template<typename _Tp>
431 struct __decay_and_strip
433 typedef typename __strip_reference_wrapper<
434 typename decay<_Tp>::type>::__type __type;
438 // Utility for constructing identically cv-qualified types.
439 template<typename _Unqualified, bool _IsConst, bool _IsVol>
440 struct __cv_selector;
442 template<typename _Unqualified>
443 struct __cv_selector<_Unqualified, false, false>
444 { typedef _Unqualified __type; };
446 template<typename _Unqualified>
447 struct __cv_selector<_Unqualified, false, true>
448 { typedef volatile _Unqualified __type; };
450 template<typename _Unqualified>
451 struct __cv_selector<_Unqualified, true, false>
452 { typedef const _Unqualified __type; };
454 template<typename _Unqualified>
455 struct __cv_selector<_Unqualified, true, true>
456 { typedef const volatile _Unqualified __type; };
458 template<typename _Qualified, typename _Unqualified,
459 bool _IsConst = is_const<_Qualified>::value,
460 bool _IsVol = is_volatile<_Qualified>::value>
461 class __match_cv_qualifiers
463 typedef __cv_selector<_Unqualified, _IsConst, _IsVol> __match;
466 typedef typename __match::__type __type;
470 // Utility for finding the unsigned versions of signed integral types.
471 template<typename _Tp>
472 struct __make_unsigned
473 { typedef _Tp __type; };
476 struct __make_unsigned<char>
477 { typedef unsigned char __type; };
480 struct __make_unsigned<signed char>
481 { typedef unsigned char __type; };
484 struct __make_unsigned<short>
485 { typedef unsigned short __type; };
488 struct __make_unsigned<int>
489 { typedef unsigned int __type; };
492 struct __make_unsigned<long>
493 { typedef unsigned long __type; };
496 struct __make_unsigned<long long>
497 { typedef unsigned long long __type; };
500 // Select between integral and enum: not possible to be both.
501 template<typename _Tp,
502 bool _IsInt = is_integral<_Tp>::value,
503 bool _IsEnum = is_enum<_Tp>::value>
504 class __make_unsigned_selector;
506 template<typename _Tp>
507 class __make_unsigned_selector<_Tp, true, false>
509 typedef __make_unsigned<typename remove_cv<_Tp>::type> __unsignedt;
510 typedef typename __unsignedt::__type __unsigned_type;
511 typedef __match_cv_qualifiers<_Tp, __unsigned_type> __cv_unsigned;
514 typedef typename __cv_unsigned::__type __type;
517 template<typename _Tp>
518 class __make_unsigned_selector<_Tp, false, true>
520 // With -fshort-enums, an enum may be as small as a char.
521 typedef unsigned char __smallest;
522 static const bool __b0 = sizeof(_Tp) <= sizeof(__smallest);
523 static const bool __b1 = sizeof(_Tp) <= sizeof(unsigned short);
524 static const bool __b2 = sizeof(_Tp) <= sizeof(unsigned int);
525 typedef conditional<__b2, unsigned int, unsigned long> __cond2;
526 typedef typename __cond2::type __cond2_type;
527 typedef conditional<__b1, unsigned short, __cond2_type> __cond1;
528 typedef typename __cond1::type __cond1_type;
531 typedef typename conditional<__b0, __smallest, __cond1_type>::type __type;
534 // Given an integral/enum type, return the corresponding unsigned
538 template<typename _Tp>
540 { typedef typename __make_unsigned_selector<_Tp>::__type type; };
542 // Integral, but don't define.
544 struct make_unsigned<bool>;
547 // Utility for finding the signed versions of unsigned integral types.
548 template<typename _Tp>
550 { typedef _Tp __type; };
553 struct __make_signed<char>
554 { typedef signed char __type; };
557 struct __make_signed<unsigned char>
558 { typedef signed char __type; };
561 struct __make_signed<unsigned short>
562 { typedef signed short __type; };
565 struct __make_signed<unsigned int>
566 { typedef signed int __type; };
569 struct __make_signed<unsigned long>
570 { typedef signed long __type; };
573 struct __make_signed<unsigned long long>
574 { typedef signed long long __type; };
577 // Select between integral and enum: not possible to be both.
578 template<typename _Tp,
579 bool _IsInt = is_integral<_Tp>::value,
580 bool _IsEnum = is_enum<_Tp>::value>
581 class __make_signed_selector;
583 template<typename _Tp>
584 class __make_signed_selector<_Tp, true, false>
586 typedef __make_signed<typename remove_cv<_Tp>::type> __signedt;
587 typedef typename __signedt::__type __signed_type;
588 typedef __match_cv_qualifiers<_Tp, __signed_type> __cv_signed;
591 typedef typename __cv_signed::__type __type;
594 template<typename _Tp>
595 class __make_signed_selector<_Tp, false, true>
597 // With -fshort-enums, an enum may be as small as a char.
598 typedef signed char __smallest;
599 static const bool __b0 = sizeof(_Tp) <= sizeof(__smallest);
600 static const bool __b1 = sizeof(_Tp) <= sizeof(signed short);
601 static const bool __b2 = sizeof(_Tp) <= sizeof(signed int);
602 typedef conditional<__b2, signed int, signed long> __cond2;
603 typedef typename __cond2::type __cond2_type;
604 typedef conditional<__b1, signed short, __cond2_type> __cond1;
605 typedef typename __cond1::type __cond1_type;
608 typedef typename conditional<__b0, __smallest, __cond1_type>::type __type;
611 // Given an integral/enum type, return the corresponding signed
615 template<typename _Tp>
617 { typedef typename __make_signed_selector<_Tp>::__type type; };
619 // Integral, but don't define.
621 struct make_signed<bool>;
624 template<typename... _Tp>
627 template<typename _Tp>
628 struct common_type<_Tp>
629 { typedef _Tp type; };
631 template<typename _Tp, typename _Up>
632 struct common_type<_Tp, _Up>
633 { typedef decltype(true ? declval<_Tp>() : declval<_Up>()) type; };
635 template<typename _Tp, typename _Up, typename... _Vp>
636 struct common_type<_Tp, _Up, _Vp...>
639 common_type<typename common_type<_Tp, _Up>::type, _Vp...>::type type;
641 // @} group metaprogramming
644 template<typename _Tp>
645 struct __declval_protector
647 static const bool __stop = false;
648 static typename add_rvalue_reference<_Tp>::type __delegate();
651 template<typename _Tp>
652 inline typename add_rvalue_reference<_Tp>::type
655 static_assert(__declval_protector<_Tp>::__stop,
656 "declval() must not be used!");
657 return __declval_protector<_Tp>::__delegate();
661 #endif // __GXX_EXPERIMENTAL_CXX0X__
663 #endif // _GLIBCXX_TYPE_TRAITS