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
110 template <class T> struct IsTriviallyCopyable
111 : std::integral_constant<bool,
112 !std::is_class<T>::value ||
113 // TODO: add alternate clause is_trivially_copyable, when available
114 traits_detail::has_true_IsTriviallyCopyable<T>::value
117 template <class T> struct IsRelocatable
118 : std::integral_constant<bool,
119 !std::is_class<T>::value ||
120 // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
121 //std::is_trivially_move_constructible<T>::value ||
122 IsTriviallyCopyable<T>::value ||
123 traits_detail::has_true_IsRelocatable<T>::value
126 template <class T> struct IsZeroInitializable
127 : std::integral_constant<bool,
128 !std::is_class<T>::value ||
129 traits_detail::has_true_IsZeroInitializable<T>::value
132 template <typename...>
133 struct Conjunction : std::true_type {};
134 template <typename T>
135 struct Conjunction<T> : T {};
136 template <typename T, typename... TList>
137 struct Conjunction<T, TList...>
138 : std::conditional<T::value, Conjunction<TList...>, T>::type {};
140 template <typename...>
141 struct Disjunction : std::false_type {};
142 template <typename T>
143 struct Disjunction<T> : T {};
144 template <typename T, typename... TList>
145 struct Disjunction<T, TList...>
146 : std::conditional<T::value, T, Disjunction<TList...>>::type {};
148 template <typename T>
149 struct Negation : std::integral_constant<bool, !T::value> {};
154 * Use this macro ONLY inside namespace folly. When using it with a
155 * regular type, use it like this:
157 * // Make sure you're at namespace ::folly scope
158 * template<> FOLLY_ASSUME_RELOCATABLE(MyType)
160 * When using it with a template type, use it like this:
162 * // Make sure you're at namespace ::folly scope
163 * template<class T1, class T2>
164 * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
166 #define FOLLY_ASSUME_RELOCATABLE(...) \
167 struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
170 * Use this macro ONLY inside namespace boost. When using it with a
171 * regular type, use it like this:
173 * // Make sure you're at namespace ::boost scope
174 * template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType)
176 * When using it with a template type, use it like this:
178 * // Make sure you're at namespace ::boost scope
179 * template<class T1, class T2>
180 * FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType<T1, T2>)
182 #define FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(...) \
183 struct has_nothrow_constructor< __VA_ARGS__ > : ::boost::true_type {};
186 * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode two
187 * assumptions: first, that the type is relocatable per IsRelocatable
188 * above, and that it has a nothrow constructor. Most types can be
189 * assumed to satisfy both conditions, but it is the responsibility of
190 * the user to state that assumption. User-defined classes will not
191 * work with fbvector (see FBVector.h) unless they state this
192 * combination of properties.
194 * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
196 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
198 * The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
199 * allow using the macro for describing templatized classes with 1, 2,
200 * 3, and 4 template parameters respectively. For template classes
201 * just use the macro with the appropriate number and pass the name of
202 * the template to it. Example:
204 * template <class T1, class T2> class MyType { ... };
206 * // Make sure you're at global scope
207 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
210 // Use this macro ONLY at global level (no namespace)
211 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
212 namespace folly { template<> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) } \
214 template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__) }
215 // Use this macro ONLY at global level (no namespace)
216 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
218 template <class T1> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) } \
220 template <class T1> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1>) }
221 // Use this macro ONLY at global level (no namespace)
222 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
224 template <class T1, class T2> \
225 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) } \
227 template <class T1, class T2> \
228 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2>) }
229 // Use this macro ONLY at global level (no namespace)
230 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
232 template <class T1, class T2, class T3> \
233 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) } \
235 template <class T1, class T2, class T3> \
236 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3>) }
237 // Use this macro ONLY at global level (no namespace)
238 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
240 template <class T1, class T2, class T3, class T4> \
241 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) } \
243 template <class T1, class T2, class T3, class T4> \
244 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3, T4>) }
247 * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
248 * safe to assume that pair is compatible if both of its components
249 * are. Furthermore, all STL containers can be assumed to comply,
250 * although that is not guaranteed by the standard.
253 FOLLY_NAMESPACE_STD_BEGIN
255 template <class T, class U>
257 #ifndef _GLIBCXX_USE_FB
258 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
259 template <class T, class R, class A>
261 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
263 template <class T, class R, class A, class S>
266 template <class T, class A>
268 template <class T, class A>
270 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
271 template <class T, class A>
273 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
274 template <class T, class C, class A>
276 template <class K, class V, class C, class A>
281 FOLLY_NAMESPACE_STD_END
285 template <class T> class shared_ptr;
287 template <class T, class U>
288 struct has_nothrow_constructor< std::pair<T, U> >
289 : std::integral_constant<bool,
290 has_nothrow_constructor<T>::value &&
291 has_nothrow_constructor<U>::value> {};
297 // STL commonly-used types
298 template <class T, class U>
299 struct IsRelocatable< std::pair<T, U> >
300 : std::integral_constant<bool,
301 IsRelocatable<T>::value &&
302 IsRelocatable<U>::value> {};
304 // Is T one of T1, T2, ..., Tn?
305 template <class T, class... Ts>
307 enum { value = false };
310 template <class T, class T1, class... Ts>
311 struct IsOneOf<T, T1, Ts...> {
312 enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
316 * Complementary type traits for integral comparisons.
318 * For instance, `if(x < 0)` yields an error in clang for unsigned types
319 * when -Werror is used due to -Wtautological-compare
322 * @author: Marcelo Juchem <marcelo@fb.com>
327 template <typename T, bool>
328 struct is_negative_impl {
329 constexpr static bool check(T x) { return x < 0; }
332 template <typename T>
333 struct is_negative_impl<T, false> {
334 constexpr static bool check(T) { return false; }
337 // folly::to integral specializations can end up generating code
338 // inside what are really static ifs (not executed because of the templated
339 // types) that violate -Wsign-compare and/or -Wbool-compare so suppress them
340 // in order to not prevent all calling code from using it.
341 #pragma GCC diagnostic push
342 #pragma GCC diagnostic ignored "-Wsign-compare"
343 #if __GNUC_PREREQ(5, 0)
344 #pragma GCC diagnostic ignored "-Wbool-compare"
347 template <typename RHS, RHS rhs, typename LHS>
348 bool less_than_impl(LHS const lhs) {
350 rhs > std::numeric_limits<LHS>::max() ? true :
351 rhs <= std::numeric_limits<LHS>::min() ? false :
355 template <typename RHS, RHS rhs, typename LHS>
356 bool greater_than_impl(LHS const lhs) {
358 rhs > std::numeric_limits<LHS>::max() ? false :
359 rhs < std::numeric_limits<LHS>::min() ? true :
363 #pragma GCC diagnostic pop
365 } // namespace detail {
368 template <typename T>
369 constexpr bool is_negative(T x) {
370 return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
374 template <typename T>
375 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
378 template <typename T>
379 constexpr bool is_positive(T x) { return !is_non_positive(x); }
382 template <typename T>
383 constexpr bool is_non_negative(T x) {
384 return !x || is_positive(x);
387 template <typename RHS, RHS rhs, typename LHS>
388 bool less_than(LHS const lhs) {
389 return detail::less_than_impl<
390 RHS, rhs, typename std::remove_reference<LHS>::type
394 template <typename RHS, RHS rhs, typename LHS>
395 bool greater_than(LHS const lhs) {
396 return detail::greater_than_impl<
397 RHS, rhs, typename std::remove_reference<LHS>::type
402 * Like std::piecewise_construct, a tag type & instance used for in-place
403 * construction of non-movable contained types, e.g. by Synchronized.
405 struct construct_in_place_t {};
406 constexpr construct_in_place_t construct_in_place{};
409 * Initializer lists are a powerful compile time syntax introduced in C++11
410 * but due to their often conflicting syntax they are not used by APIs for
413 * Further standard conforming compilers *strongly* favor an
414 * std::initalizer_list overload for construction if one exists. The
415 * following is a simple tag used to disambiguate construction with
416 * initializer lists and regular uniform initialization.
418 * For example consider the following case
422 * explicit Something(int);
423 * Something(std::intiializer_list<int>);
429 * Something something{1}; // SURPRISE!!
431 * The last call to instantiate the Something object will go to the
432 * initializer_list overload. Which may be surprising to users.
434 * If however this tag was used to disambiguate such construction it would be
435 * easy for users to see which construction overload their code was referring
440 * explicit Something(int);
441 * Something(folly::initlist_construct_t, std::initializer_list<int>);
447 * Something something_one{1}; // not the initializer_list overload
448 * Something something_two{folly::initlist_construct, {1}}; // correct
450 struct initlist_construct_t {};
451 constexpr initlist_construct_t initlist_construct{};
455 // gcc-5.0 changed string's implementation in libgcc to be non-relocatable
457 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string)
459 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector)
460 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list)
461 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque)
462 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr)
463 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr)
464 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function)
467 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(boost::shared_ptr)
469 #define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name) \
470 template <typename T> \
472 template <typename C> \
473 constexpr static bool test(typename C::type_name*) { return true; } \
474 template <typename> \
475 constexpr static bool test(...) { return false; } \
476 constexpr static bool value = test<T>(nullptr); \
479 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
480 template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
481 class classname<TTheClass_, RTheReturn_(TTheArgs_...) cv_qual> { \
483 typename UTheClass_, RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual \
484 > struct sfinae {}; \
485 template <typename UTheClass_> \
486 constexpr static bool test(sfinae<UTheClass_, &UTheClass_::func_name>*) \
488 template <typename> \
489 constexpr static bool test(...) { return false; } \
491 constexpr static bool value = test<TTheClass_>(nullptr); \
495 * The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
496 * classes that check for the existence of a member function with
497 * a given name and signature. It currently does not support
498 * checking for inherited members.
500 * Such classes receive two template parameters: the class to be checked
501 * and the signature of the member function. A static boolean field
502 * named `value` (which is also constexpr) tells whether such member
505 * Each traits class created is bound only to the member name, not to
506 * its signature nor to the type of the class containing it.
508 * Say you need to know if a given class has a member function named
509 * `test` with the following signature:
513 * You'd need this macro to create a traits class to check for a member
514 * named `test`, and then use this traits class to check for the signature:
518 * FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
520 * } // unnamed-namespace
523 * cout << "Does class Foo have a member int test() const? "
524 * << boolalpha << has_test_traits<Foo, int() const>::value;
527 * You can use the same traits class to test for a completely different
528 * signature, on a completely different class, as long as the member name
532 * cout << "Does class Foo have a member int test()? "
533 * << boolalpha << has_test_traits<Foo, int()>::value;
534 * cout << "Does class Foo have a member int test() const? "
535 * << boolalpha << has_test_traits<Foo, int() const>::value;
536 * cout << "Does class Bar have a member double test(const string&, long)? "
537 * << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
540 * @author: Marcelo Juchem <marcelo@fb.com>
542 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name) \
543 template <typename, typename> class classname; \
544 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, ); \
545 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const); \
546 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
547 classname, func_name, /* nolint */ volatile); \
548 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
549 classname, func_name, /* nolint */ volatile const)