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
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;
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 {};
177 * There is a bug in libstdc++, libc++, and MSVC's STL that causes it to
178 * ignore unused template parameter arguments in template aliases and does not
179 * cause substitution failures. This defect has been recorded here:
180 * http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1558.
182 * This causes the implementation of std::void_t to be buggy, as it is likely
183 * defined as something like the following:
185 * template <typename...>
186 * using void_t = void;
188 * This causes the compiler to ignore all the template arguments and does not
189 * help when one wants to cause substitution failures. Rather declarations
190 * which have void_t in orthogonal specializations are treated as the same.
191 * For example, assuming the possible `T` types are only allowed to have
192 * either the alias `one` or `two` and never both or none:
194 * template <typename T,
195 * typename std::void_t<std::decay_t<T>::one>* = nullptr>
197 * template <typename T,
198 * typename std::void_t<std::decay_t<T>::two>* = nullptr>
201 * The second foo() will be a redefinition because it conflicts with the first
202 * one; void_t does not cause substitution failures - the template types are
206 namespace traits_detail {
211 } // namespace traits_detail
213 template <class... Ts>
214 using void_t = _t<traits_detail::void_t_<Ts...>>;
217 * IsRelocatable<T>::value describes the ability of moving around
218 * memory a value of type T by using memcpy (as opposed to the
219 * conservative approach of calling the copy constructor and then
220 * destroying the old temporary. Essentially for a relocatable type,
221 * the following two sequences of code should be semantically
224 * void move1(T * from, T * to) {
229 * void move2(T * from, T * to) {
230 * memcpy(to, from, sizeof(T));
233 * Most C++ types are relocatable; the ones that aren't would include
234 * internal pointers or (very rarely) would need to update remote
235 * pointers to pointers tracking them. All C++ primitive types and
236 * type constructors are relocatable.
238 * This property can be used in a variety of optimizations. Currently
239 * fbvector uses this property intensively.
241 * The default conservatively assumes the type is not
242 * relocatable. Several specializations are defined for known
243 * types. You may want to add your own specializations. Do so in
244 * namespace folly and make sure you keep the specialization of
245 * IsRelocatable<SomeStruct> in the same header as SomeStruct.
247 * You may also declare a type to be relocatable by including
248 * `typedef std::true_type IsRelocatable;`
249 * in the class header.
251 * It may be unset in a base class by overriding the typedef to false_type.
254 * IsTriviallyCopyable describes the value semantics property. C++11 contains
255 * the type trait is_trivially_copyable; however, it is not yet implemented
256 * in gcc (as of 4.7.1), and the user may wish to specify otherwise.
259 * IsZeroInitializable describes the property that default construction is the
260 * same as memset(dst, 0, sizeof(T)).
263 namespace traits_detail {
265 #define FOLLY_HAS_TRUE_XXX(name) \
266 FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(has_##name, name); \
268 struct name##_is_true : std::is_same<typename T::name, std::true_type> {}; \
270 struct has_true_##name : std::conditional< \
271 has_##name<T>::value, \
273 std::false_type>::type {};
275 FOLLY_HAS_TRUE_XXX(IsRelocatable)
276 FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
277 FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
279 #undef FOLLY_HAS_TRUE_XXX
281 // Older versions of libstdc++ do not provide std::is_trivially_copyable
282 #if defined(__clang__) && !defined(_LIBCPP_VERSION)
284 struct is_trivially_copyable
285 : std::integral_constant<bool, __is_trivially_copyable(T)> {};
286 #elif defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
288 struct is_trivially_copyable : std::is_trivial<T> {};
291 using is_trivially_copyable = std::is_trivially_copyable<T>;
297 /* implicit */ Ignore(const T&) {}
299 const Ignore& operator=(T const&) const { return *this; }
303 using Ignored = Ignore;
305 namespace traits_detail_IsEqualityComparable {
306 Ignore operator==(Ignore, Ignore);
308 template <class T, class U = T>
309 struct IsEqualityComparable
310 : std::is_convertible<
311 decltype(std::declval<T>() == std::declval<U>()),
316 /* using override */ using traits_detail_IsEqualityComparable::
317 IsEqualityComparable;
319 namespace traits_detail_IsLessThanComparable {
320 Ignore operator<(Ignore, Ignore);
322 template <class T, class U = T>
323 struct IsLessThanComparable
324 : std::is_convertible<
325 decltype(std::declval<T>() < std::declval<U>()),
330 /* using override */ using traits_detail_IsLessThanComparable::
331 IsLessThanComparable;
333 namespace traits_detail_IsNothrowSwappable {
334 #if defined(__cpp_lib_is_swappable) || (_CPPLIB_VER && _HAS_CXX17)
335 // MSVC 2015+ already implements the C++17 P0185R1 proposal which
336 // adds std::is_nothrow_swappable, so use it instead if C++17 mode
338 template <typename T>
339 using IsNothrowSwappable = std::is_nothrow_swappable<T>;
341 // MSVC 2015+ defines the base even if C++17 is disabled, and
342 // MSVC 2015 has issues with our fallback implementation due to
343 // over-eager evaluation of noexcept.
344 template <typename T>
345 using IsNothrowSwappable = std::_Is_nothrow_swappable<T>;
347 /* using override */ using std::swap;
350 struct IsNothrowSwappable
351 : std::integral_constant<bool,
352 std::is_nothrow_move_constructible<T>::value &&
353 noexcept(swap(std::declval<T&>(), std::declval<T&>()))
358 /* using override */ using traits_detail_IsNothrowSwappable::IsNothrowSwappable;
360 template <class T> struct IsTriviallyCopyable
362 traits_detail::has_IsTriviallyCopyable<T>::value,
363 traits_detail::has_true_IsTriviallyCopyable<T>,
364 traits_detail::is_trivially_copyable<T>
367 template <class T> struct IsRelocatable
369 traits_detail::has_IsRelocatable<T>::value,
370 traits_detail::has_true_IsRelocatable<T>,
371 // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
372 //std::is_trivially_move_constructible<T>::value ||
373 IsTriviallyCopyable<T>
376 template <class T> struct IsZeroInitializable
378 traits_detail::has_IsZeroInitializable<T>::value,
379 traits_detail::has_true_IsZeroInitializable<T>,
380 std::integral_constant<bool, !std::is_class<T>::value>
383 template <typename...>
384 struct Conjunction : std::true_type {};
385 template <typename T>
386 struct Conjunction<T> : T {};
387 template <typename T, typename... TList>
388 struct Conjunction<T, TList...>
389 : std::conditional<T::value, Conjunction<TList...>, T>::type {};
391 template <typename...>
392 struct Disjunction : std::false_type {};
393 template <typename T>
394 struct Disjunction<T> : T {};
395 template <typename T, typename... TList>
396 struct Disjunction<T, TList...>
397 : std::conditional<T::value, T, Disjunction<TList...>>::type {};
399 template <typename T>
400 struct Negation : std::integral_constant<bool, !T::value> {};
402 template <bool... Bs>
404 using valid_type = bool;
405 static constexpr std::size_t size() {
406 return sizeof...(Bs);
410 // Lighter-weight than Conjunction, but evaluates all sub-conditions eagerly.
411 template <class... Ts>
412 struct StrictConjunction
413 : std::is_same<Bools<Ts::value...>, Bools<(Ts::value || true)...>> {};
415 template <class... Ts>
416 struct StrictDisjunction
418 std::is_same<Bools<Ts::value...>, Bools<(Ts::value && false)...>>
424 * Use this macro ONLY inside namespace folly. When using it with a
425 * regular type, use it like this:
427 * // Make sure you're at namespace ::folly scope
428 * template <> FOLLY_ASSUME_RELOCATABLE(MyType)
430 * When using it with a template type, use it like this:
432 * // Make sure you're at namespace ::folly scope
433 * template <class T1, class T2>
434 * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
436 #define FOLLY_ASSUME_RELOCATABLE(...) \
437 struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
440 * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode the
441 * assumption that the type is relocatable per IsRelocatable
442 * above. Many types can be assumed to satisfy this condition, but
443 * it is the responsibility of the user to state that assumption.
444 * User-defined classes will not be optimized for use with
445 * fbvector (see FBVector.h) unless they state that assumption.
447 * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
449 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
451 * The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
452 * allow using the macro for describing templatized classes with 1, 2,
453 * 3, and 4 template parameters respectively. For template classes
454 * just use the macro with the appropriate number and pass the name of
455 * the template to it. Example:
457 * template <class T1, class T2> class MyType { ... };
459 * // Make sure you're at global scope
460 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
463 // Use this macro ONLY at global level (no namespace)
464 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
467 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) \
469 // Use this macro ONLY at global level (no namespace)
470 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
472 template <class T1> \
473 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) \
475 // Use this macro ONLY at global level (no namespace)
476 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
478 template <class T1, class T2> \
479 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) \
481 // Use this macro ONLY at global level (no namespace)
482 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
484 template <class T1, class T2, class T3> \
485 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) \
487 // Use this macro ONLY at global level (no namespace)
488 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
490 template <class T1, class T2, class T3, class T4> \
491 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) \
495 * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
496 * safe to assume that pair is compatible if both of its components
497 * are. Furthermore, all STL containers can be assumed to comply,
498 * although that is not guaranteed by the standard.
501 FOLLY_NAMESPACE_STD_BEGIN
503 template <class T, class U>
505 #ifndef _GLIBCXX_USE_FB
506 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
507 template <class T, class R, class A>
509 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
511 template <class T, class R, class A, class S>
514 template <class T, class A>
516 template <class T, class A>
518 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
519 template <class T, class A>
521 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
522 template <class T, class C, class A>
524 template <class K, class V, class C, class A>
529 FOLLY_NAMESPACE_STD_END
533 // STL commonly-used types
534 template <class T, class U>
535 struct IsRelocatable< std::pair<T, U> >
536 : std::integral_constant<bool,
537 IsRelocatable<T>::value &&
538 IsRelocatable<U>::value> {};
540 // Is T one of T1, T2, ..., Tn?
541 template <typename T, typename... Ts>
542 using IsOneOf = StrictDisjunction<std::is_same<T, Ts>...>;
545 * Complementary type traits for integral comparisons.
547 * For instance, `if(x < 0)` yields an error in clang for unsigned types
548 * when -Werror is used due to -Wtautological-compare
551 * @author: Marcelo Juchem <marcelo@fb.com>
556 template <typename T, bool>
557 struct is_negative_impl {
558 constexpr static bool check(T x) { return x < 0; }
561 template <typename T>
562 struct is_negative_impl<T, false> {
563 constexpr static bool check(T) { return false; }
566 // folly::to integral specializations can end up generating code
567 // inside what are really static ifs (not executed because of the templated
568 // types) that violate -Wsign-compare and/or -Wbool-compare so suppress them
569 // in order to not prevent all calling code from using it.
571 FOLLY_GCC_DISABLE_WARNING("-Wsign-compare")
572 #if __GNUC_PREREQ(5, 0)
573 FOLLY_GCC_DISABLE_WARNING("-Wbool-compare")
575 FOLLY_MSVC_DISABLE_WARNING(4388) // sign-compare
576 FOLLY_MSVC_DISABLE_WARNING(4804) // bool-compare
578 template <typename RHS, RHS rhs, typename LHS>
579 bool less_than_impl(LHS const lhs) {
581 rhs > std::numeric_limits<LHS>::max() ? true :
582 rhs <= std::numeric_limits<LHS>::min() ? false :
586 template <typename RHS, RHS rhs, typename LHS>
587 bool greater_than_impl(LHS const lhs) {
589 rhs > std::numeric_limits<LHS>::max() ? false :
590 rhs < std::numeric_limits<LHS>::min() ? true :
596 } // namespace detail
599 template <typename T>
600 constexpr bool is_negative(T x) {
601 return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
605 template <typename T>
606 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
609 template <typename T>
610 constexpr bool is_positive(T x) { return !is_non_positive(x); }
613 template <typename T>
614 constexpr bool is_non_negative(T x) {
615 return !x || is_positive(x);
618 template <typename RHS, RHS rhs, typename LHS>
619 bool less_than(LHS const lhs) {
620 return detail::less_than_impl<
621 RHS, rhs, typename std::remove_reference<LHS>::type
625 template <typename RHS, RHS rhs, typename LHS>
626 bool greater_than(LHS const lhs) {
627 return detail::greater_than_impl<
628 RHS, rhs, typename std::remove_reference<LHS>::type
633 // Assume nothing when compiling with MSVC.
635 // gcc-5.0 changed string's implementation in libstdc++ to be non-relocatable
636 #if !_GLIBCXX_USE_CXX11_ABI
637 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string)
639 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector)
640 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list)
641 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque)
642 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr)
643 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr)
644 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function)
647 /* Some combinations of compilers and C++ libraries make __int128 and
648 * unsigned __int128 available but do not correctly define their standard type
651 * If FOLLY_SUPPLY_MISSING_INT128_TRAITS is defined, we define these traits
654 * @author: Phil Willoughby <philwill@fb.com>
656 #if FOLLY_SUPPLY_MISSING_INT128_TRAITS
657 FOLLY_NAMESPACE_STD_BEGIN
659 struct is_arithmetic<__int128> : ::std::true_type {};
661 struct is_arithmetic<unsigned __int128> : ::std::true_type {};
663 struct is_integral<__int128> : ::std::true_type {};
665 struct is_integral<unsigned __int128> : ::std::true_type {};
667 struct make_unsigned<__int128> {
668 typedef unsigned __int128 type;
671 struct make_signed<__int128> {
672 typedef __int128 type;
675 struct make_unsigned<unsigned __int128> {
676 typedef unsigned __int128 type;
679 struct make_signed<unsigned __int128> {
680 typedef __int128 type;
683 struct is_signed<__int128> : ::std::true_type {};
685 struct is_unsigned<unsigned __int128> : ::std::true_type {};
686 FOLLY_NAMESPACE_STD_END
687 #endif // FOLLY_SUPPLY_MISSING_INT128_TRAITS