2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 // @author: Andrei Alexandrescu
23 #include <type_traits>
26 #include <folly/Portability.h>
28 // libc++ doesn't provide this header, nor does msvc
29 #ifdef FOLLY_HAVE_BITS_CXXCONFIG_H
30 // This file appears in two locations: inside fbcode and in the
31 // libstdc++ source code (when embedding fbstring as std::string).
32 // To aid in this schizophrenic use, two macros are defined in
34 // _LIBSTDCXX_FBSTRING - Set inside libstdc++. This is useful to
35 // gate use inside fbcode v. libstdc++
36 #include <bits/c++config.h>
39 #include <boost/type_traits.hpp>
40 #include <boost/mpl/has_xxx.hpp>
45 * IsRelocatable<T>::value describes the ability of moving around
46 * memory a value of type T by using memcpy (as opposed to the
47 * conservative approach of calling the copy constructor and then
48 * destroying the old temporary. Essentially for a relocatable type,
49 * the following two sequences of code should be semantically
52 * void move1(T * from, T * to) {
57 * void move2(T * from, T * to) {
58 * memcpy(to, from, sizeof(T));
61 * Most C++ types are relocatable; the ones that aren't would include
62 * internal pointers or (very rarely) would need to update remote
63 * pointers to pointers tracking them. All C++ primitive types and
64 * type constructors are relocatable.
66 * This property can be used in a variety of optimizations. Currently
67 * fbvector uses this property intensively.
69 * The default conservatively assumes the type is not
70 * relocatable. Several specializations are defined for known
71 * types. You may want to add your own specializations. Do so in
72 * namespace folly and make sure you keep the specialization of
73 * IsRelocatable<SomeStruct> in the same header as SomeStruct.
75 * You may also declare a type to be relocatable by including
76 * `typedef std::true_type IsRelocatable;`
77 * in the class header.
79 * It may be unset in a base class by overriding the typedef to false_type.
82 * IsTriviallyCopyable describes the value semantics property. C++11 contains
83 * the type trait is_trivially_copyable; however, it is not yet implemented
84 * in gcc (as of 4.7.1), and the user may wish to specify otherwise.
87 * IsZeroInitializable describes the property that default construction is the
88 * same as memset(dst, 0, sizeof(T)).
91 namespace traits_detail {
93 #define FOLLY_HAS_TRUE_XXX(name) \
94 BOOST_MPL_HAS_XXX_TRAIT_DEF(name) \
96 struct name##_is_true : std::is_same<typename T::name, std::true_type> {}; \
98 struct has_true_##name : std::conditional< \
99 has_##name<T>::value, \
101 std::false_type>::type {};
103 FOLLY_HAS_TRUE_XXX(IsRelocatable)
104 FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
105 FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
107 #undef FOLLY_HAS_TRUE_XXX
109 // Older versions of libstdc++ do not provide std::is_trivially_copyable
110 #if defined(__clang__) && !defined(_LIBCPP_VERSION)
112 struct is_trivially_copyable
113 : std::integral_constant<bool, __is_trivially_copyable(T)> {};
114 #elif defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
116 struct is_trivially_copyable : std::is_trivial<T> {};
119 using is_trivially_copyable = std::is_trivially_copyable<T>;
125 /* implicit */ Ignore(const T&) {}
127 const Ignore& operator=(T const&) const { return *this; }
131 using Ignored = Ignore;
133 namespace traits_detail_IsEqualityComparable {
134 Ignore operator==(Ignore, Ignore);
136 template <class T, class U = T>
137 struct IsEqualityComparable
138 : std::is_convertible<
139 decltype(std::declval<T>() == std::declval<U>()),
144 /* using override */ using traits_detail_IsEqualityComparable::
145 IsEqualityComparable;
147 namespace traits_detail_IsLessThanComparable {
148 Ignore operator<(Ignore, Ignore);
150 template <class T, class U = T>
151 struct IsLessThanComparable
152 : std::is_convertible<
153 decltype(std::declval<T>() < std::declval<U>()),
158 /* using override */ using traits_detail_IsLessThanComparable::
159 IsLessThanComparable;
161 namespace traits_detail_IsNothrowSwappable {
162 #if defined(_MSC_VER) || defined(__cpp_lib_is_swappable)
163 // MSVC already implements the C++17 P0185R1 proposal which
164 // adds std::is_nothrow_swappable, so use it instead.
165 template <typename T>
166 using IsNothrowSwappable = std::is_nothrow_swappable<T>;
168 /* using override */ using std::swap;
171 struct IsNothrowSwappable
172 : std::integral_constant<bool,
173 std::is_nothrow_move_constructible<T>::value &&
174 noexcept(swap(std::declval<T&>(), std::declval<T&>()))
179 /* using override */ using traits_detail_IsNothrowSwappable::IsNothrowSwappable;
181 template <class T> struct IsTriviallyCopyable
183 traits_detail::has_IsTriviallyCopyable<T>::value,
184 traits_detail::has_true_IsTriviallyCopyable<T>,
185 traits_detail::is_trivially_copyable<T>
188 template <class T> struct IsRelocatable
190 traits_detail::has_IsRelocatable<T>::value,
191 traits_detail::has_true_IsRelocatable<T>,
192 // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
193 //std::is_trivially_move_constructible<T>::value ||
194 IsTriviallyCopyable<T>
197 template <class T> struct IsZeroInitializable
199 traits_detail::has_IsZeroInitializable<T>::value,
200 traits_detail::has_true_IsZeroInitializable<T>,
201 std::integral_constant<bool, !std::is_class<T>::value>
204 template <typename...>
205 struct Conjunction : std::true_type {};
206 template <typename T>
207 struct Conjunction<T> : T {};
208 template <typename T, typename... TList>
209 struct Conjunction<T, TList...>
210 : std::conditional<T::value, Conjunction<TList...>, T>::type {};
212 template <typename...>
213 struct Disjunction : std::false_type {};
214 template <typename T>
215 struct Disjunction<T> : T {};
216 template <typename T, typename... TList>
217 struct Disjunction<T, TList...>
218 : std::conditional<T::value, T, Disjunction<TList...>>::type {};
220 template <typename T>
221 struct Negation : std::integral_constant<bool, !T::value> {};
223 template <bool... Bs>
225 using valid_type = bool;
226 static constexpr std::size_t size() {
227 return sizeof...(Bs);
231 // Lighter-weight than Conjunction, but evaluates all sub-conditions eagerly.
232 template <class... Ts>
233 using StrictConjunction =
234 std::is_same<Bools<Ts::value..., true>, Bools<true, Ts::value...>>;
239 * Use this macro ONLY inside namespace folly. When using it with a
240 * regular type, use it like this:
242 * // Make sure you're at namespace ::folly scope
243 * template<> FOLLY_ASSUME_RELOCATABLE(MyType)
245 * When using it with a template type, use it like this:
247 * // Make sure you're at namespace ::folly scope
248 * template<class T1, class T2>
249 * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
251 #define FOLLY_ASSUME_RELOCATABLE(...) \
252 struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
255 * Use this macro ONLY inside namespace boost. When using it with a
256 * regular type, use it like this:
258 * // Make sure you're at namespace ::boost scope
259 * template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType)
261 * When using it with a template type, use it like this:
263 * // Make sure you're at namespace ::boost scope
264 * template<class T1, class T2>
265 * FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType<T1, T2>)
267 #define FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(...) \
268 struct has_nothrow_constructor< __VA_ARGS__ > : ::boost::true_type {};
271 * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode two
272 * assumptions: first, that the type is relocatable per IsRelocatable
273 * above, and that it has a nothrow constructor. Most types can be
274 * assumed to satisfy both conditions, but it is the responsibility of
275 * the user to state that assumption. User-defined classes will not
276 * work with fbvector (see FBVector.h) unless they state this
277 * combination of properties.
279 * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
281 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
283 * The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
284 * allow using the macro for describing templatized classes with 1, 2,
285 * 3, and 4 template parameters respectively. For template classes
286 * just use the macro with the appropriate number and pass the name of
287 * the template to it. Example:
289 * template <class T1, class T2> class MyType { ... };
291 * // Make sure you're at global scope
292 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
295 // Use this macro ONLY at global level (no namespace)
296 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
297 namespace folly { template<> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) } \
299 template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__) }
300 // Use this macro ONLY at global level (no namespace)
301 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
303 template <class T1> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) } \
305 template <class T1> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1>) }
306 // Use this macro ONLY at global level (no namespace)
307 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
309 template <class T1, class T2> \
310 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) } \
312 template <class T1, class T2> \
313 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2>) }
314 // Use this macro ONLY at global level (no namespace)
315 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
317 template <class T1, class T2, class T3> \
318 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) } \
320 template <class T1, class T2, class T3> \
321 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3>) }
322 // Use this macro ONLY at global level (no namespace)
323 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
325 template <class T1, class T2, class T3, class T4> \
326 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) } \
328 template <class T1, class T2, class T3, class T4> \
329 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3, T4>) }
332 * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
333 * safe to assume that pair is compatible if both of its components
334 * are. Furthermore, all STL containers can be assumed to comply,
335 * although that is not guaranteed by the standard.
338 FOLLY_NAMESPACE_STD_BEGIN
340 template <class T, class U>
342 #ifndef _GLIBCXX_USE_FB
343 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
344 template <class T, class R, class A>
346 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
348 template <class T, class R, class A, class S>
351 template <class T, class A>
353 template <class T, class A>
355 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
356 template <class T, class A>
358 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
359 template <class T, class C, class A>
361 template <class K, class V, class C, class A>
366 FOLLY_NAMESPACE_STD_END
370 template <class T> class shared_ptr;
372 template <class T, class U>
373 struct has_nothrow_constructor< std::pair<T, U> >
374 : std::integral_constant<bool,
375 has_nothrow_constructor<T>::value &&
376 has_nothrow_constructor<U>::value> {};
382 // STL commonly-used types
383 template <class T, class U>
384 struct IsRelocatable< std::pair<T, U> >
385 : std::integral_constant<bool,
386 IsRelocatable<T>::value &&
387 IsRelocatable<U>::value> {};
389 // Is T one of T1, T2, ..., Tn?
390 template <class T, class... Ts>
392 enum { value = false };
395 template <class T, class T1, class... Ts>
396 struct IsOneOf<T, T1, Ts...> {
397 enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
401 * Complementary type traits for integral comparisons.
403 * For instance, `if(x < 0)` yields an error in clang for unsigned types
404 * when -Werror is used due to -Wtautological-compare
407 * @author: Marcelo Juchem <marcelo@fb.com>
412 template <typename T, bool>
413 struct is_negative_impl {
414 constexpr static bool check(T x) { return x < 0; }
417 template <typename T>
418 struct is_negative_impl<T, false> {
419 constexpr static bool check(T) { return false; }
422 // folly::to integral specializations can end up generating code
423 // inside what are really static ifs (not executed because of the templated
424 // types) that violate -Wsign-compare and/or -Wbool-compare so suppress them
425 // in order to not prevent all calling code from using it.
427 FOLLY_GCC_DISABLE_WARNING(sign-compare)
428 #if __GNUC_PREREQ(5, 0)
429 FOLLY_GCC_DISABLE_WARNING(bool-compare)
431 FOLLY_MSVC_DISABLE_WARNING(4388) // sign-compare
432 FOLLY_MSVC_DISABLE_WARNING(4804) // bool-compare
434 template <typename RHS, RHS rhs, typename LHS>
435 bool less_than_impl(LHS const lhs) {
437 rhs > std::numeric_limits<LHS>::max() ? true :
438 rhs <= std::numeric_limits<LHS>::min() ? false :
442 template <typename RHS, RHS rhs, typename LHS>
443 bool greater_than_impl(LHS const lhs) {
445 rhs > std::numeric_limits<LHS>::max() ? false :
446 rhs < std::numeric_limits<LHS>::min() ? true :
452 } // namespace detail {
455 template <typename T>
456 constexpr bool is_negative(T x) {
457 return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
461 template <typename T>
462 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
465 template <typename T>
466 constexpr bool is_positive(T x) { return !is_non_positive(x); }
469 template <typename T>
470 constexpr bool is_non_negative(T x) {
471 return !x || is_positive(x);
474 template <typename RHS, RHS rhs, typename LHS>
475 bool less_than(LHS const lhs) {
476 return detail::less_than_impl<
477 RHS, rhs, typename std::remove_reference<LHS>::type
481 template <typename RHS, RHS rhs, typename LHS>
482 bool greater_than(LHS const lhs) {
483 return detail::greater_than_impl<
484 RHS, rhs, typename std::remove_reference<LHS>::type
488 namespace traits_detail {
489 struct InPlaceTag {};
491 struct InPlaceTypeTag {};
492 template <std::size_t>
493 struct InPlaceIndexTag {};
497 * Like std::piecewise_construct, a tag type & instance used for in-place
498 * construction of non-movable contained types, e.g. by Synchronized.
499 * Follows the naming and design of std::in_place suggested in
500 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0032r2.pdf
502 using in_place_t = traits_detail::InPlaceTag (&)(traits_detail::InPlaceTag);
505 using in_place_type_t =
506 traits_detail::InPlaceTypeTag<T> (&)(traits_detail::InPlaceTypeTag<T>);
508 template <std::size_t I>
509 using in_place_index_t =
510 traits_detail::InPlaceIndexTag<I> (&)(traits_detail::InPlaceIndexTag<I>);
512 inline traits_detail::InPlaceTag in_place(traits_detail::InPlaceTag = {}) {
517 inline traits_detail::InPlaceTypeTag<T> in_place(
518 traits_detail::InPlaceTypeTag<T> = {}) {
522 template <std::size_t I>
523 inline traits_detail::InPlaceIndexTag<I> in_place(
524 traits_detail::InPlaceIndexTag<I> = {}) {
528 // For backwards compatibility:
529 using construct_in_place_t = in_place_t;
531 inline traits_detail::InPlaceTag construct_in_place(
532 traits_detail::InPlaceTag = {}) {
537 * Initializer lists are a powerful compile time syntax introduced in C++11
538 * but due to their often conflicting syntax they are not used by APIs for
541 * Further standard conforming compilers *strongly* favor an
542 * std::initalizer_list overload for construction if one exists. The
543 * following is a simple tag used to disambiguate construction with
544 * initializer lists and regular uniform initialization.
546 * For example consider the following case
550 * explicit Something(int);
551 * Something(std::intiializer_list<int>);
557 * Something something{1}; // SURPRISE!!
559 * The last call to instantiate the Something object will go to the
560 * initializer_list overload. Which may be surprising to users.
562 * If however this tag was used to disambiguate such construction it would be
563 * easy for users to see which construction overload their code was referring
568 * explicit Something(int);
569 * Something(folly::initlist_construct_t, std::initializer_list<int>);
575 * Something something_one{1}; // not the initializer_list overload
576 * Something something_two{folly::initlist_construct, {1}}; // correct
578 struct initlist_construct_t {};
579 constexpr initlist_construct_t initlist_construct{};
583 // Assume nothing when compiling with MSVC.
585 // gcc-5.0 changed string's implementation in libgcc to be non-relocatable
587 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string)
589 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector)
590 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list)
591 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque)
592 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr)
593 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr)
594 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function)
597 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(boost::shared_ptr)
600 #define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name) \
601 template <typename T> \
603 template <typename C> \
604 constexpr static bool test(typename C::type_name*) { return true; } \
605 template <typename> \
606 constexpr static bool test(...) { return false; } \
607 constexpr static bool value = test<T>(nullptr); \
610 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
611 template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
612 class classname<TTheClass_, RTheReturn_(TTheArgs_...) cv_qual> { \
614 typename UTheClass_, RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual \
615 > struct sfinae {}; \
616 template <typename UTheClass_> \
617 constexpr static bool test(sfinae<UTheClass_, &UTheClass_::func_name>*) \
619 template <typename> \
620 constexpr static bool test(...) { return false; } \
622 constexpr static bool value = test<TTheClass_>(nullptr); \
626 * The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
627 * classes that check for the existence of a member function with
628 * a given name and signature. It currently does not support
629 * checking for inherited members.
631 * Such classes receive two template parameters: the class to be checked
632 * and the signature of the member function. A static boolean field
633 * named `value` (which is also constexpr) tells whether such member
636 * Each traits class created is bound only to the member name, not to
637 * its signature nor to the type of the class containing it.
639 * Say you need to know if a given class has a member function named
640 * `test` with the following signature:
644 * You'd need this macro to create a traits class to check for a member
645 * named `test`, and then use this traits class to check for the signature:
649 * FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
651 * } // unnamed-namespace
654 * cout << "Does class Foo have a member int test() const? "
655 * << boolalpha << has_test_traits<Foo, int() const>::value;
658 * You can use the same traits class to test for a completely different
659 * signature, on a completely different class, as long as the member name
663 * cout << "Does class Foo have a member int test()? "
664 * << boolalpha << has_test_traits<Foo, int()>::value;
665 * cout << "Does class Foo have a member int test() const? "
666 * << boolalpha << has_test_traits<Foo, int() const>::value;
667 * cout << "Does class Bar have a member double test(const string&, long)? "
668 * << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
671 * @author: Marcelo Juchem <marcelo@fb.com>
673 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name) \
674 template <typename, typename> class classname; \
675 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, ); \
676 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const); \
677 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
678 classname, func_name, /* nolint */ volatile); \
679 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
680 classname, func_name, /* nolint */ volatile const)
682 /* Some combinations of compilers and C++ libraries make __int128 and
683 * unsigned __int128 available but do not correctly define their standard type
686 * If FOLLY_SUPPLY_MISSING_INT128_TRAITS is defined, we define these traits
689 * @author: Phil Willoughby <philwill@fb.com>
691 #if FOLLY_SUPPLY_MISSING_INT128_TRAITS
692 FOLLY_NAMESPACE_STD_BEGIN
694 struct is_arithmetic<__int128> : ::std::true_type {};
696 struct is_arithmetic<unsigned __int128> : ::std::true_type {};
698 struct is_integral<__int128> : ::std::true_type {};
700 struct is_integral<unsigned __int128> : ::std::true_type {};
702 struct make_unsigned<__int128> {
703 typedef unsigned __int128 type;
706 struct make_signed<__int128> {
707 typedef __int128 type;
710 struct make_unsigned<unsigned __int128> {
711 typedef unsigned __int128 type;
714 struct make_signed<unsigned __int128> {
715 typedef __int128 type;
718 struct is_signed<__int128> : ::std::true_type {};
720 struct is_unsigned<unsigned __int128> : ::std::true_type {};
721 FOLLY_NAMESPACE_STD_END
722 #endif // FOLLY_SUPPLY_MISSING_INT128_TRAITS