2 * Copyright 2017 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 #define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name) \
40 template <typename TTheClass_> \
41 struct classname##__folly_traits_impl__ { \
42 template <typename UTheClass_> \
43 static constexpr bool test(typename UTheClass_::type_name*) { \
47 static constexpr bool test(...) { \
51 template <typename TTheClass_> \
52 using classname = typename std::conditional< \
53 classname##__folly_traits_impl__<TTheClass_>::template test<TTheClass_>( \
56 std::false_type>::type;
58 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
59 template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
60 struct classname##__folly_traits_impl__< \
62 RTheReturn_(TTheArgs_...) cv_qual> { \
64 typename UTheClass_, \
65 RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual> \
67 template <typename UTheClass_> \
68 static std::true_type test(sfinae<UTheClass_, &UTheClass_::func_name>*); \
70 static std::false_type test(...); \
74 * The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
75 * classes that check for the existence of a member function with
76 * a given name and signature. It currently does not support
77 * checking for inherited members.
79 * Such classes receive two template parameters: the class to be checked
80 * and the signature of the member function. A static boolean field
81 * named `value` (which is also constexpr) tells whether such member
84 * Each traits class created is bound only to the member name, not to
85 * its signature nor to the type of the class containing it.
87 * Say you need to know if a given class has a member function named
88 * `test` with the following signature:
92 * You'd need this macro to create a traits class to check for a member
93 * named `test`, and then use this traits class to check for the signature:
97 * FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
99 * } // unnamed-namespace
102 * cout << "Does class Foo have a member int test() const? "
103 * << boolalpha << has_test_traits<Foo, int() const>::value;
106 * You can use the same traits class to test for a completely different
107 * signature, on a completely different class, as long as the member name
111 * cout << "Does class Foo have a member int test()? "
112 * << boolalpha << has_test_traits<Foo, int()>::value;
113 * cout << "Does class Foo have a member int test() const? "
114 * << boolalpha << has_test_traits<Foo, int() const>::value;
115 * cout << "Does class Bar have a member double test(const string&, long)? "
116 * << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
119 * @author: Marcelo Juchem <marcelo@fb.com>
121 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name) \
122 template <typename, typename> \
123 struct classname##__folly_traits_impl__; \
124 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, ); \
125 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const); \
126 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
127 classname, func_name, /* nolint */ volatile); \
128 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
129 classname, func_name, /* nolint */ volatile const); \
130 template <typename TTheClass_, typename TTheSignature_> \
132 decltype(classname##__folly_traits_impl__<TTheClass_, TTheSignature_>:: \
133 template test<TTheClass_>(nullptr))
142 * using decayed = typename std::decay<T>::type;
144 * With the C++14 standard trait aliases, we could use:
146 * using decayed = std::decay_t<T>;
148 * Without them, we could use:
150 * using decayed = _t<std::decay<T>>;
152 * Also useful for any other library with template types having dependent
153 * member types named `type`, like the standard trait types.
155 template <typename T>
156 using _t = typename T::type;
161 * A type alias for `void`. `void_t` is useful for controling class-template
162 * partial specialization.
166 * // has_value_type<T>::value is true if T has a nested type `value_type`
167 * template <class T, class = void>
168 * struct has_value_type
169 * : std::false_type {};
172 * struct has_value_type<T, folly::void_t<typename T::value_type>>
173 * : std::true_type {};
175 #if defined(__cpp_lib_void_t) || defined(_MSC_VER)
177 /* using override */ using std::void_t;
179 #else // defined(__cpp_lib_void_t) || defined(_MSC_VER)
181 namespace traits_detail {
186 } // namespace traits_detail
188 template <class... Ts>
189 using void_t = _t<traits_detail::void_t_<Ts...>>;
191 #endif // defined(__cpp_lib_void_t) || defined(_MSC_VER)
194 * IsRelocatable<T>::value describes the ability of moving around
195 * memory a value of type T by using memcpy (as opposed to the
196 * conservative approach of calling the copy constructor and then
197 * destroying the old temporary. Essentially for a relocatable type,
198 * the following two sequences of code should be semantically
201 * void move1(T * from, T * to) {
206 * void move2(T * from, T * to) {
207 * memcpy(to, from, sizeof(T));
210 * Most C++ types are relocatable; the ones that aren't would include
211 * internal pointers or (very rarely) would need to update remote
212 * pointers to pointers tracking them. All C++ primitive types and
213 * type constructors are relocatable.
215 * This property can be used in a variety of optimizations. Currently
216 * fbvector uses this property intensively.
218 * The default conservatively assumes the type is not
219 * relocatable. Several specializations are defined for known
220 * types. You may want to add your own specializations. Do so in
221 * namespace folly and make sure you keep the specialization of
222 * IsRelocatable<SomeStruct> in the same header as SomeStruct.
224 * You may also declare a type to be relocatable by including
225 * `typedef std::true_type IsRelocatable;`
226 * in the class header.
228 * It may be unset in a base class by overriding the typedef to false_type.
231 * IsTriviallyCopyable describes the value semantics property. C++11 contains
232 * the type trait is_trivially_copyable; however, it is not yet implemented
233 * in gcc (as of 4.7.1), and the user may wish to specify otherwise.
236 * IsZeroInitializable describes the property that default construction is the
237 * same as memset(dst, 0, sizeof(T)).
240 namespace traits_detail {
242 #define FOLLY_HAS_TRUE_XXX(name) \
243 FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(has_##name, name); \
245 struct name##_is_true : std::is_same<typename T::name, std::true_type> {}; \
247 struct has_true_##name : std::conditional< \
248 has_##name<T>::value, \
250 std::false_type>::type {};
252 FOLLY_HAS_TRUE_XXX(IsRelocatable)
253 FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
254 FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
256 #undef FOLLY_HAS_TRUE_XXX
258 // Older versions of libstdc++ do not provide std::is_trivially_copyable
259 #if defined(__clang__) && !defined(_LIBCPP_VERSION)
261 struct is_trivially_copyable
262 : std::integral_constant<bool, __is_trivially_copyable(T)> {};
263 #elif defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
265 struct is_trivially_copyable : std::is_trivial<T> {};
268 using is_trivially_copyable = std::is_trivially_copyable<T>;
274 /* implicit */ Ignore(const T&) {}
276 const Ignore& operator=(T const&) const { return *this; }
280 using Ignored = Ignore;
282 namespace traits_detail_IsEqualityComparable {
283 Ignore operator==(Ignore, Ignore);
285 template <class T, class U = T>
286 struct IsEqualityComparable
287 : std::is_convertible<
288 decltype(std::declval<T>() == std::declval<U>()),
293 /* using override */ using traits_detail_IsEqualityComparable::
294 IsEqualityComparable;
296 namespace traits_detail_IsLessThanComparable {
297 Ignore operator<(Ignore, Ignore);
299 template <class T, class U = T>
300 struct IsLessThanComparable
301 : std::is_convertible<
302 decltype(std::declval<T>() < std::declval<U>()),
307 /* using override */ using traits_detail_IsLessThanComparable::
308 IsLessThanComparable;
310 namespace traits_detail_IsNothrowSwappable {
311 #if defined(__cpp_lib_is_swappable) || (_CPPLIB_VER && _HAS_CXX17)
312 // MSVC 2015+ already implements the C++17 P0185R1 proposal which
313 // adds std::is_nothrow_swappable, so use it instead if C++17 mode
315 template <typename T>
316 using IsNothrowSwappable = std::is_nothrow_swappable<T>;
318 // MSVC 2015+ defines the base even if C++17 is disabled, and
319 // MSVC 2015 has issues with our fallback implementation due to
320 // over-eager evaluation of noexcept.
321 template <typename T>
322 using IsNothrowSwappable = std::_Is_nothrow_swappable<T>;
324 /* using override */ using std::swap;
327 struct IsNothrowSwappable
328 : std::integral_constant<bool,
329 std::is_nothrow_move_constructible<T>::value &&
330 noexcept(swap(std::declval<T&>(), std::declval<T&>()))
335 /* using override */ using traits_detail_IsNothrowSwappable::IsNothrowSwappable;
337 template <class T> struct IsTriviallyCopyable
339 traits_detail::has_IsTriviallyCopyable<T>::value,
340 traits_detail::has_true_IsTriviallyCopyable<T>,
341 traits_detail::is_trivially_copyable<T>
344 template <class T> struct IsRelocatable
346 traits_detail::has_IsRelocatable<T>::value,
347 traits_detail::has_true_IsRelocatable<T>,
348 // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
349 //std::is_trivially_move_constructible<T>::value ||
350 IsTriviallyCopyable<T>
353 template <class T> struct IsZeroInitializable
355 traits_detail::has_IsZeroInitializable<T>::value,
356 traits_detail::has_true_IsZeroInitializable<T>,
357 std::integral_constant<bool, !std::is_class<T>::value>
360 template <typename...>
361 struct Conjunction : std::true_type {};
362 template <typename T>
363 struct Conjunction<T> : T {};
364 template <typename T, typename... TList>
365 struct Conjunction<T, TList...>
366 : std::conditional<T::value, Conjunction<TList...>, T>::type {};
368 template <typename...>
369 struct Disjunction : std::false_type {};
370 template <typename T>
371 struct Disjunction<T> : T {};
372 template <typename T, typename... TList>
373 struct Disjunction<T, TList...>
374 : std::conditional<T::value, T, Disjunction<TList...>>::type {};
376 template <typename T>
377 struct Negation : std::integral_constant<bool, !T::value> {};
379 template <bool... Bs>
381 using valid_type = bool;
382 static constexpr std::size_t size() {
383 return sizeof...(Bs);
387 // Lighter-weight than Conjunction, but evaluates all sub-conditions eagerly.
388 template <class... Ts>
389 struct StrictConjunction
390 : std::is_same<Bools<Ts::value..., true>, Bools<true, Ts::value...>> {};
395 * Use this macro ONLY inside namespace folly. When using it with a
396 * regular type, use it like this:
398 * // Make sure you're at namespace ::folly scope
399 * template<> FOLLY_ASSUME_RELOCATABLE(MyType)
401 * When using it with a template type, use it like this:
403 * // Make sure you're at namespace ::folly scope
404 * template<class T1, class T2>
405 * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
407 #define FOLLY_ASSUME_RELOCATABLE(...) \
408 struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
411 * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode the
412 * assumption that the type is relocatable per IsRelocatable
413 * above. Many types can be assumed to satisfy this condition, but
414 * it is the responsibility of the user to state that assumption.
415 * User-defined classes will not be optimized for use with
416 * fbvector (see FBVector.h) unless they state that assumption.
418 * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
420 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
422 * The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
423 * allow using the macro for describing templatized classes with 1, 2,
424 * 3, and 4 template parameters respectively. For template classes
425 * just use the macro with the appropriate number and pass the name of
426 * the template to it. Example:
428 * template <class T1, class T2> class MyType { ... };
430 * // Make sure you're at global scope
431 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
434 // Use this macro ONLY at global level (no namespace)
435 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
438 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) \
440 // Use this macro ONLY at global level (no namespace)
441 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
443 template <class T1> \
444 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) \
446 // Use this macro ONLY at global level (no namespace)
447 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
449 template <class T1, class T2> \
450 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) \
452 // Use this macro ONLY at global level (no namespace)
453 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
455 template <class T1, class T2, class T3> \
456 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) \
458 // Use this macro ONLY at global level (no namespace)
459 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
461 template <class T1, class T2, class T3, class T4> \
462 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) \
466 * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
467 * safe to assume that pair is compatible if both of its components
468 * are. Furthermore, all STL containers can be assumed to comply,
469 * although that is not guaranteed by the standard.
472 FOLLY_NAMESPACE_STD_BEGIN
474 template <class T, class U>
476 #ifndef _GLIBCXX_USE_FB
477 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
478 template <class T, class R, class A>
480 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
482 template <class T, class R, class A, class S>
485 template <class T, class A>
487 template <class T, class A>
489 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
490 template <class T, class A>
492 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
493 template <class T, class C, class A>
495 template <class K, class V, class C, class A>
500 FOLLY_NAMESPACE_STD_END
504 // STL commonly-used types
505 template <class T, class U>
506 struct IsRelocatable< std::pair<T, U> >
507 : std::integral_constant<bool,
508 IsRelocatable<T>::value &&
509 IsRelocatable<U>::value> {};
511 // Is T one of T1, T2, ..., Tn?
512 template <class T, class... Ts>
514 enum { value = false };
517 template <class T, class T1, class... Ts>
518 struct IsOneOf<T, T1, Ts...> {
519 enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
523 * Complementary type traits for integral comparisons.
525 * For instance, `if(x < 0)` yields an error in clang for unsigned types
526 * when -Werror is used due to -Wtautological-compare
529 * @author: Marcelo Juchem <marcelo@fb.com>
534 template <typename T, bool>
535 struct is_negative_impl {
536 constexpr static bool check(T x) { return x < 0; }
539 template <typename T>
540 struct is_negative_impl<T, false> {
541 constexpr static bool check(T) { return false; }
544 // folly::to integral specializations can end up generating code
545 // inside what are really static ifs (not executed because of the templated
546 // types) that violate -Wsign-compare and/or -Wbool-compare so suppress them
547 // in order to not prevent all calling code from using it.
549 FOLLY_GCC_DISABLE_WARNING("-Wsign-compare")
550 #if __GNUC_PREREQ(5, 0)
551 FOLLY_GCC_DISABLE_WARNING("-Wbool-compare")
553 FOLLY_MSVC_DISABLE_WARNING(4388) // sign-compare
554 FOLLY_MSVC_DISABLE_WARNING(4804) // bool-compare
556 template <typename RHS, RHS rhs, typename LHS>
557 bool less_than_impl(LHS const lhs) {
559 rhs > std::numeric_limits<LHS>::max() ? true :
560 rhs <= std::numeric_limits<LHS>::min() ? false :
564 template <typename RHS, RHS rhs, typename LHS>
565 bool greater_than_impl(LHS const lhs) {
567 rhs > std::numeric_limits<LHS>::max() ? false :
568 rhs < std::numeric_limits<LHS>::min() ? true :
574 } // namespace detail {
577 template <typename T>
578 constexpr bool is_negative(T x) {
579 return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
583 template <typename T>
584 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
587 template <typename T>
588 constexpr bool is_positive(T x) { return !is_non_positive(x); }
591 template <typename T>
592 constexpr bool is_non_negative(T x) {
593 return !x || is_positive(x);
596 template <typename RHS, RHS rhs, typename LHS>
597 bool less_than(LHS const lhs) {
598 return detail::less_than_impl<
599 RHS, rhs, typename std::remove_reference<LHS>::type
603 template <typename RHS, RHS rhs, typename LHS>
604 bool greater_than(LHS const lhs) {
605 return detail::greater_than_impl<
606 RHS, rhs, typename std::remove_reference<LHS>::type
610 namespace traits_detail {
611 struct InPlaceTag {};
613 struct InPlaceTypeTag {};
614 template <std::size_t>
615 struct InPlaceIndexTag {};
619 * Like std::piecewise_construct, a tag type & instance used for in-place
620 * construction of non-movable contained types, e.g. by Synchronized.
621 * Follows the naming and design of std::in_place suggested in
622 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0032r2.pdf
624 using in_place_t = traits_detail::InPlaceTag (&)(traits_detail::InPlaceTag);
627 using in_place_type_t =
628 traits_detail::InPlaceTypeTag<T> (&)(traits_detail::InPlaceTypeTag<T>);
630 template <std::size_t I>
631 using in_place_index_t =
632 traits_detail::InPlaceIndexTag<I> (&)(traits_detail::InPlaceIndexTag<I>);
634 inline traits_detail::InPlaceTag in_place(traits_detail::InPlaceTag = {}) {
639 inline traits_detail::InPlaceTypeTag<T> in_place(
640 traits_detail::InPlaceTypeTag<T> = {}) {
644 template <std::size_t I>
645 inline traits_detail::InPlaceIndexTag<I> in_place(
646 traits_detail::InPlaceIndexTag<I> = {}) {
650 // For backwards compatibility:
651 using construct_in_place_t = in_place_t;
653 inline traits_detail::InPlaceTag construct_in_place(
654 traits_detail::InPlaceTag = {}) {
659 * Initializer lists are a powerful compile time syntax introduced in C++11
660 * but due to their often conflicting syntax they are not used by APIs for
663 * Further standard conforming compilers *strongly* favor an
664 * std::initalizer_list overload for construction if one exists. The
665 * following is a simple tag used to disambiguate construction with
666 * initializer lists and regular uniform initialization.
668 * For example consider the following case
672 * explicit Something(int);
673 * Something(std::intiializer_list<int>);
679 * Something something{1}; // SURPRISE!!
681 * The last call to instantiate the Something object will go to the
682 * initializer_list overload. Which may be surprising to users.
684 * If however this tag was used to disambiguate such construction it would be
685 * easy for users to see which construction overload their code was referring
690 * explicit Something(int);
691 * Something(folly::initlist_construct_t, std::initializer_list<int>);
697 * Something something_one{1}; // not the initializer_list overload
698 * Something something_two{folly::initlist_construct, {1}}; // correct
700 struct initlist_construct_t {};
701 constexpr initlist_construct_t initlist_construct{};
705 // Assume nothing when compiling with MSVC.
707 // gcc-5.0 changed string's implementation in libstdc++ to be non-relocatable
708 #if !_GLIBCXX_USE_CXX11_ABI
709 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string)
711 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector)
712 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list)
713 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque)
714 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr)
715 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr)
716 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function)
719 /* Some combinations of compilers and C++ libraries make __int128 and
720 * unsigned __int128 available but do not correctly define their standard type
723 * If FOLLY_SUPPLY_MISSING_INT128_TRAITS is defined, we define these traits
726 * @author: Phil Willoughby <philwill@fb.com>
728 #if FOLLY_SUPPLY_MISSING_INT128_TRAITS
729 FOLLY_NAMESPACE_STD_BEGIN
731 struct is_arithmetic<__int128> : ::std::true_type {};
733 struct is_arithmetic<unsigned __int128> : ::std::true_type {};
735 struct is_integral<__int128> : ::std::true_type {};
737 struct is_integral<unsigned __int128> : ::std::true_type {};
739 struct make_unsigned<__int128> {
740 typedef unsigned __int128 type;
743 struct make_signed<__int128> {
744 typedef __int128 type;
747 struct make_unsigned<unsigned __int128> {
748 typedef unsigned __int128 type;
751 struct make_signed<unsigned __int128> {
752 typedef __int128 type;
755 struct is_signed<__int128> : ::std::true_type {};
757 struct is_unsigned<unsigned __int128> : ::std::true_type {};
758 FOLLY_NAMESPACE_STD_END
759 #endif // FOLLY_SUPPLY_MISSING_INT128_TRAITS