2 * Copyright 2011-present 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
24 #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;
159 * A type trait to remove all const volatile and reference qualifiers on a
162 template <typename T>
163 struct remove_cvref {
165 typename std::remove_cv<typename std::remove_reference<T>::type>::type;
167 template <typename T>
168 using remove_cvref_t = typename remove_cvref<T>::type;
173 * A type alias for the first template type argument. `type_t` is useful for
174 * controlling class-template and function-template partial specialization.
178 * template <typename Value>
181 * template <typename... Args>
183 * type_t<in_place_t, decltype(Value(std::declval<Args>()...))>,
189 * A type alias for `void`. `void_t` is useful for controling class-template
190 * and function-template partial specialization.
194 * // has_value_type<T>::value is true if T has a nested type `value_type`
195 * template <class T, class = void>
196 * struct has_value_type
197 * : std::false_type {};
200 * struct has_value_type<T, folly::void_t<typename T::value_type>>
201 * : std::true_type {};
205 * There is a bug in libstdc++, libc++, and MSVC's STL that causes it to
206 * ignore unused template parameter arguments in template aliases and does not
207 * cause substitution failures. This defect has been recorded here:
208 * http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1558.
210 * This causes the implementation of std::void_t to be buggy, as it is likely
211 * defined as something like the following:
213 * template <typename...>
214 * using void_t = void;
216 * This causes the compiler to ignore all the template arguments and does not
217 * help when one wants to cause substitution failures. Rather declarations
218 * which have void_t in orthogonal specializations are treated as the same.
219 * For example, assuming the possible `T` types are only allowed to have
220 * either the alias `one` or `two` and never both or none:
222 * template <typename T,
223 * typename std::void_t<std::decay_t<T>::one>* = nullptr>
225 * template <typename T,
226 * typename std::void_t<std::decay_t<T>::two>* = nullptr>
229 * The second foo() will be a redefinition because it conflicts with the first
230 * one; void_t does not cause substitution failures - the template types are
234 namespace traits_detail {
235 template <class T, class...>
239 } // namespace traits_detail
241 template <class T, class... Ts>
242 using type_t = typename traits_detail::type_t_<T, Ts...>::type;
243 template <class... Ts>
244 using void_t = type_t<void, Ts...>;
247 * IsRelocatable<T>::value describes the ability of moving around
248 * memory a value of type T by using memcpy (as opposed to the
249 * conservative approach of calling the copy constructor and then
250 * destroying the old temporary. Essentially for a relocatable type,
251 * the following two sequences of code should be semantically
254 * void move1(T * from, T * to) {
259 * void move2(T * from, T * to) {
260 * memcpy(to, from, sizeof(T));
263 * Most C++ types are relocatable; the ones that aren't would include
264 * internal pointers or (very rarely) would need to update remote
265 * pointers to pointers tracking them. All C++ primitive types and
266 * type constructors are relocatable.
268 * This property can be used in a variety of optimizations. Currently
269 * fbvector uses this property intensively.
271 * The default conservatively assumes the type is not
272 * relocatable. Several specializations are defined for known
273 * types. You may want to add your own specializations. Do so in
274 * namespace folly and make sure you keep the specialization of
275 * IsRelocatable<SomeStruct> in the same header as SomeStruct.
277 * You may also declare a type to be relocatable by including
278 * `typedef std::true_type IsRelocatable;`
279 * in the class header.
281 * It may be unset in a base class by overriding the typedef to false_type.
284 * IsTriviallyCopyable describes the value semantics property. C++11 contains
285 * the type trait is_trivially_copyable; however, it is not yet implemented
286 * in gcc (as of 4.7.1), and the user may wish to specify otherwise.
289 * IsZeroInitializable describes the property that default construction is the
290 * same as memset(dst, 0, sizeof(T)).
293 namespace traits_detail {
295 #define FOLLY_HAS_TRUE_XXX(name) \
296 FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(has_##name, name); \
298 struct name##_is_true : std::is_same<typename T::name, std::true_type> {}; \
300 struct has_true_##name : std::conditional< \
301 has_##name<T>::value, \
303 std::false_type>::type {};
305 FOLLY_HAS_TRUE_XXX(IsRelocatable)
306 FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
307 FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
309 #undef FOLLY_HAS_TRUE_XXX
311 // Older versions of libstdc++ do not provide std::is_trivially_copyable
312 #if defined(__clang__) && !defined(_LIBCPP_VERSION)
314 struct is_trivially_copyable
315 : std::integral_constant<bool, __is_trivially_copyable(T)> {};
316 #elif defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
318 struct is_trivially_copyable : std::is_trivial<T> {};
321 using is_trivially_copyable = std::is_trivially_copyable<T>;
323 } // namespace traits_detail
328 constexpr /* implicit */ Ignore(const T&) {}
330 const Ignore& operator=(T const&) const { return *this; }
334 using Ignored = Ignore;
336 namespace traits_detail_IsEqualityComparable {
337 Ignore operator==(Ignore, Ignore);
339 template <class T, class U = T>
340 struct IsEqualityComparable
341 : std::is_convertible<
342 decltype(std::declval<T>() == std::declval<U>()),
345 } // namespace traits_detail_IsEqualityComparable
347 /* using override */ using traits_detail_IsEqualityComparable::
348 IsEqualityComparable;
350 namespace traits_detail_IsLessThanComparable {
351 Ignore operator<(Ignore, Ignore);
353 template <class T, class U = T>
354 struct IsLessThanComparable
355 : std::is_convertible<
356 decltype(std::declval<T>() < std::declval<U>()),
359 } // namespace traits_detail_IsLessThanComparable
361 /* using override */ using traits_detail_IsLessThanComparable::
362 IsLessThanComparable;
364 namespace traits_detail_IsNothrowSwappable {
365 #if defined(__cpp_lib_is_swappable) || (_CPPLIB_VER && _HAS_CXX17)
366 // MSVC 2015+ already implements the C++17 P0185R1 proposal which
367 // adds std::is_nothrow_swappable, so use it instead if C++17 mode
369 template <typename T>
370 using IsNothrowSwappable = std::is_nothrow_swappable<T>;
372 // MSVC 2015+ defines the base even if C++17 is disabled, and
373 // MSVC 2015 has issues with our fallback implementation due to
374 // over-eager evaluation of noexcept.
375 template <typename T>
376 using IsNothrowSwappable = std::_Is_nothrow_swappable<T>;
378 /* using override */ using std::swap;
381 struct IsNothrowSwappable
382 : std::integral_constant<bool,
383 std::is_nothrow_move_constructible<T>::value &&
384 noexcept(swap(std::declval<T&>(), std::declval<T&>()))
387 } // namespace traits_detail_IsNothrowSwappable
389 /* using override */ using traits_detail_IsNothrowSwappable::IsNothrowSwappable;
391 template <class T> struct IsTriviallyCopyable
393 traits_detail::has_IsTriviallyCopyable<T>::value,
394 traits_detail::has_true_IsTriviallyCopyable<T>,
395 traits_detail::is_trivially_copyable<T>
398 template <class T> struct IsRelocatable
400 traits_detail::has_IsRelocatable<T>::value,
401 traits_detail::has_true_IsRelocatable<T>,
402 // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
403 //std::is_trivially_move_constructible<T>::value ||
404 IsTriviallyCopyable<T>
407 template <class T> struct IsZeroInitializable
409 traits_detail::has_IsZeroInitializable<T>::value,
410 traits_detail::has_true_IsZeroInitializable<T>,
411 std::integral_constant<bool, !std::is_class<T>::value>
414 template <typename...>
415 struct Conjunction : std::true_type {};
416 template <typename T>
417 struct Conjunction<T> : T {};
418 template <typename T, typename... TList>
419 struct Conjunction<T, TList...>
420 : std::conditional<T::value, Conjunction<TList...>, T>::type {};
422 template <typename...>
423 struct Disjunction : std::false_type {};
424 template <typename T>
425 struct Disjunction<T> : T {};
426 template <typename T, typename... TList>
427 struct Disjunction<T, TList...>
428 : std::conditional<T::value, T, Disjunction<TList...>>::type {};
430 template <typename T>
431 struct Negation : std::integral_constant<bool, !T::value> {};
433 template <bool... Bs>
435 using valid_type = bool;
436 static constexpr std::size_t size() {
437 return sizeof...(Bs);
441 // Lighter-weight than Conjunction, but evaluates all sub-conditions eagerly.
442 template <class... Ts>
443 struct StrictConjunction
444 : std::is_same<Bools<Ts::value...>, Bools<(Ts::value || true)...>> {};
446 template <class... Ts>
447 struct StrictDisjunction
449 std::is_same<Bools<Ts::value...>, Bools<(Ts::value && false)...>>
455 * Use this macro ONLY inside namespace folly. When using it with a
456 * regular type, use it like this:
458 * // Make sure you're at namespace ::folly scope
459 * template <> FOLLY_ASSUME_RELOCATABLE(MyType)
461 * When using it with a template type, use it like this:
463 * // Make sure you're at namespace ::folly scope
464 * template <class T1, class T2>
465 * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
467 #define FOLLY_ASSUME_RELOCATABLE(...) \
468 struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
471 * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode the
472 * assumption that the type is relocatable per IsRelocatable
473 * above. Many types can be assumed to satisfy this condition, but
474 * it is the responsibility of the user to state that assumption.
475 * User-defined classes will not be optimized for use with
476 * fbvector (see FBVector.h) unless they state that assumption.
478 * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
480 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
482 * The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
483 * allow using the macro for describing templatized classes with 1, 2,
484 * 3, and 4 template parameters respectively. For template classes
485 * just use the macro with the appropriate number and pass the name of
486 * the template to it. Example:
488 * template <class T1, class T2> class MyType { ... };
490 * // Make sure you're at global scope
491 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
494 // Use this macro ONLY at global level (no namespace)
495 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
498 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) \
500 // Use this macro ONLY at global level (no namespace)
501 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
503 template <class T1> \
504 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) \
506 // Use this macro ONLY at global level (no namespace)
507 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
509 template <class T1, class T2> \
510 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) \
512 // Use this macro ONLY at global level (no namespace)
513 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
515 template <class T1, class T2, class T3> \
516 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) \
518 // Use this macro ONLY at global level (no namespace)
519 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
521 template <class T1, class T2, class T3, class T4> \
522 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) \
526 * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
527 * safe to assume that pair is compatible if both of its components
528 * are. Furthermore, all STL containers can be assumed to comply,
529 * although that is not guaranteed by the standard.
532 FOLLY_NAMESPACE_STD_BEGIN
534 template <class T, class U>
536 #ifndef _GLIBCXX_USE_FB
537 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
538 template <class T, class R, class A>
540 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
542 template <class T, class R, class A, class S>
545 template <class T, class A>
547 template <class T, class A>
549 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
550 template <class T, class A>
552 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
553 template <class T, class C, class A>
555 template <class K, class V, class C, class A>
560 FOLLY_NAMESPACE_STD_END
564 // STL commonly-used types
565 template <class T, class U>
566 struct IsRelocatable< std::pair<T, U> >
567 : std::integral_constant<bool,
568 IsRelocatable<T>::value &&
569 IsRelocatable<U>::value> {};
571 // Is T one of T1, T2, ..., Tn?
572 template <typename T, typename... Ts>
573 using IsOneOf = StrictDisjunction<std::is_same<T, Ts>...>;
576 * Complementary type traits for integral comparisons.
578 * For instance, `if(x < 0)` yields an error in clang for unsigned types
579 * when -Werror is used due to -Wtautological-compare
582 * @author: Marcelo Juchem <marcelo@fb.com>
587 template <typename T, bool>
588 struct is_negative_impl {
589 constexpr static bool check(T x) { return x < 0; }
592 template <typename T>
593 struct is_negative_impl<T, false> {
594 constexpr static bool check(T) { return false; }
597 // folly::to integral specializations can end up generating code
598 // inside what are really static ifs (not executed because of the templated
599 // types) that violate -Wsign-compare and/or -Wbool-compare so suppress them
600 // in order to not prevent all calling code from using it.
602 FOLLY_GCC_DISABLE_WARNING("-Wsign-compare")
603 #if __GNUC_PREREQ(5, 0)
604 FOLLY_GCC_DISABLE_WARNING("-Wbool-compare")
606 FOLLY_MSVC_DISABLE_WARNING(4388) // sign-compare
607 FOLLY_MSVC_DISABLE_WARNING(4804) // bool-compare
609 template <typename RHS, RHS rhs, typename LHS>
610 bool less_than_impl(LHS const lhs) {
612 rhs > std::numeric_limits<LHS>::max() ? true :
613 rhs <= std::numeric_limits<LHS>::min() ? false :
617 template <typename RHS, RHS rhs, typename LHS>
618 bool greater_than_impl(LHS const lhs) {
620 rhs > std::numeric_limits<LHS>::max() ? false :
621 rhs < std::numeric_limits<LHS>::min() ? true :
627 } // namespace detail
630 template <typename T>
631 constexpr bool is_negative(T x) {
632 return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
636 template <typename T>
637 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
640 template <typename T>
641 constexpr bool is_positive(T x) { return !is_non_positive(x); }
644 template <typename T>
645 constexpr bool is_non_negative(T x) {
646 return !x || is_positive(x);
649 template <typename RHS, RHS rhs, typename LHS>
650 bool less_than(LHS const lhs) {
651 return detail::less_than_impl<
652 RHS, rhs, typename std::remove_reference<LHS>::type
656 template <typename RHS, RHS rhs, typename LHS>
657 bool greater_than(LHS const lhs) {
658 return detail::greater_than_impl<
659 RHS, rhs, typename std::remove_reference<LHS>::type
664 // Assume nothing when compiling with MSVC.
666 // gcc-5.0 changed string's implementation in libstdc++ to be non-relocatable
667 #if !_GLIBCXX_USE_CXX11_ABI
668 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string)
670 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector)
671 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list)
672 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque)
673 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr)
674 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr)
675 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function)
678 /* Some combinations of compilers and C++ libraries make __int128 and
679 * unsigned __int128 available but do not correctly define their standard type
682 * If FOLLY_SUPPLY_MISSING_INT128_TRAITS is defined, we define these traits
685 * @author: Phil Willoughby <philwill@fb.com>
687 #if FOLLY_SUPPLY_MISSING_INT128_TRAITS
688 FOLLY_NAMESPACE_STD_BEGIN
690 struct is_arithmetic<__int128> : ::std::true_type {};
692 struct is_arithmetic<unsigned __int128> : ::std::true_type {};
694 struct is_integral<__int128> : ::std::true_type {};
696 struct is_integral<unsigned __int128> : ::std::true_type {};
698 struct make_unsigned<__int128> {
699 typedef unsigned __int128 type;
702 struct make_signed<__int128> {
703 typedef __int128 type;
706 struct make_unsigned<unsigned __int128> {
707 typedef unsigned __int128 type;
710 struct make_signed<unsigned __int128> {
711 typedef __int128 type;
714 struct is_signed<__int128> : ::std::true_type {};
716 struct is_unsigned<unsigned __int128> : ::std::true_type {};
717 FOLLY_NAMESPACE_STD_END
718 #endif // FOLLY_SUPPLY_MISSING_INT128_TRAITS