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); \
95 template <class T> struct name ## _is_true \
96 : std::is_same<typename T::name, std::true_type> {}; \
97 template <class T> struct has_true_ ## name \
99 has_ ## name <T>::value, \
100 name ## _is_true<T>, \
104 FOLLY_HAS_TRUE_XXX(IsRelocatable)
105 FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
106 FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
108 #undef FOLLY_HAS_TRUE_XXX
111 template <class T> struct IsTriviallyCopyable
112 : std::integral_constant<bool,
113 !std::is_class<T>::value ||
114 // TODO: add alternate clause is_trivially_copyable, when available
115 traits_detail::has_true_IsTriviallyCopyable<T>::value
118 template <class T> struct IsRelocatable
119 : std::integral_constant<bool,
120 !std::is_class<T>::value ||
121 // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
122 //std::is_trivially_move_constructible<T>::value ||
123 IsTriviallyCopyable<T>::value ||
124 traits_detail::has_true_IsRelocatable<T>::value
127 template <class T> struct IsZeroInitializable
128 : std::integral_constant<bool,
129 !std::is_class<T>::value ||
130 traits_detail::has_true_IsZeroInitializable<T>::value
133 template <typename...>
134 struct Conjunction : std::true_type {};
135 template <typename T>
136 struct Conjunction<T> : T {};
137 template <typename T, typename... TList>
138 struct Conjunction<T, TList...>
139 : std::conditional<T::value, Conjunction<TList...>, T>::type {};
141 template <typename...>
142 struct Disjunction : std::false_type {};
143 template <typename T>
144 struct Disjunction<T> : T {};
145 template <typename T, typename... TList>
146 struct Disjunction<T, TList...>
147 : std::conditional<T::value, T, Disjunction<TList...>>::type {};
149 template <typename T>
150 struct Negation : std::integral_constant<bool, !T::value> {};
155 * Use this macro ONLY inside namespace folly. When using it with a
156 * regular type, use it like this:
158 * // Make sure you're at namespace ::folly scope
159 * template<> FOLLY_ASSUME_RELOCATABLE(MyType)
161 * When using it with a template type, use it like this:
163 * // Make sure you're at namespace ::folly scope
164 * template<class T1, class T2>
165 * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
167 #define FOLLY_ASSUME_RELOCATABLE(...) \
168 struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
171 * Use this macro ONLY inside namespace boost. When using it with a
172 * regular type, use it like this:
174 * // Make sure you're at namespace ::boost scope
175 * template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType)
177 * When using it with a template type, use it like this:
179 * // Make sure you're at namespace ::boost scope
180 * template<class T1, class T2>
181 * FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType<T1, T2>)
183 #define FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(...) \
184 struct has_nothrow_constructor< __VA_ARGS__ > : ::boost::true_type {};
187 * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode two
188 * assumptions: first, that the type is relocatable per IsRelocatable
189 * above, and that it has a nothrow constructor. Most types can be
190 * assumed to satisfy both conditions, but it is the responsibility of
191 * the user to state that assumption. User-defined classes will not
192 * work with fbvector (see FBVector.h) unless they state this
193 * combination of properties.
195 * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
197 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
199 * The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
200 * allow using the macro for describing templatized classes with 1, 2,
201 * 3, and 4 template parameters respectively. For template classes
202 * just use the macro with the appropriate number and pass the name of
203 * the template to it. Example:
205 * template <class T1, class T2> class MyType { ... };
207 * // Make sure you're at global scope
208 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
211 // Use this macro ONLY at global level (no namespace)
212 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
213 namespace folly { template<> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) } \
215 template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__) }
216 // Use this macro ONLY at global level (no namespace)
217 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
219 template <class T1> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) } \
221 template <class T1> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1>) }
222 // Use this macro ONLY at global level (no namespace)
223 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
225 template <class T1, class T2> \
226 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) } \
228 template <class T1, class T2> \
229 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2>) }
230 // Use this macro ONLY at global level (no namespace)
231 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
233 template <class T1, class T2, class T3> \
234 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) } \
236 template <class T1, class T2, class T3> \
237 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3>) }
238 // Use this macro ONLY at global level (no namespace)
239 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
241 template <class T1, class T2, class T3, class T4> \
242 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) } \
244 template <class T1, class T2, class T3, class T4> \
245 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3, T4>) }
248 * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
249 * safe to assume that pair is compatible if both of its components
250 * are. Furthermore, all STL containers can be assumed to comply,
251 * although that is not guaranteed by the standard.
254 FOLLY_NAMESPACE_STD_BEGIN
256 template <class T, class U>
258 #ifndef _GLIBCXX_USE_FB
259 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
260 template <class T, class R, class A>
262 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
264 template <class T, class R, class A, class S>
267 template <class T, class A>
269 template <class T, class A>
271 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
272 template <class T, class A>
274 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
275 template <class T, class C, class A>
277 template <class K, class V, class C, class A>
282 FOLLY_NAMESPACE_STD_END
286 template <class T> class shared_ptr;
288 template <class T, class U>
289 struct has_nothrow_constructor< std::pair<T, U> >
290 : std::integral_constant<bool,
291 has_nothrow_constructor<T>::value &&
292 has_nothrow_constructor<U>::value> {};
298 // STL commonly-used types
299 template <class T, class U>
300 struct IsRelocatable< std::pair<T, U> >
301 : std::integral_constant<bool,
302 IsRelocatable<T>::value &&
303 IsRelocatable<U>::value> {};
305 // Is T one of T1, T2, ..., Tn?
306 template <class T, class... Ts>
308 enum { value = false };
311 template <class T, class T1, class... Ts>
312 struct IsOneOf<T, T1, Ts...> {
313 enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
317 * Complementary type traits for integral comparisons.
319 * For instance, `if(x < 0)` yields an error in clang for unsigned types
320 * when -Werror is used due to -Wtautological-compare
323 * @author: Marcelo Juchem <marcelo@fb.com>
328 template <typename T, bool>
329 struct is_negative_impl {
330 constexpr static bool check(T x) { return x < 0; }
333 template <typename T>
334 struct is_negative_impl<T, false> {
335 constexpr static bool check(T) { return false; }
338 // folly::to integral specializations can end up generating code
339 // inside what are really static ifs (not executed because of the templated
340 // types) that violate -Wsign-compare and/or -Wbool-compare so suppress them
341 // in order to not prevent all calling code from using it.
342 #pragma GCC diagnostic push
343 #pragma GCC diagnostic ignored "-Wsign-compare"
344 #if __GNUC_PREREQ(5, 0)
345 #pragma GCC diagnostic ignored "-Wbool-compare"
348 template <typename RHS, RHS rhs, typename LHS>
349 bool less_than_impl(LHS const lhs) {
351 rhs > std::numeric_limits<LHS>::max() ? true :
352 rhs <= std::numeric_limits<LHS>::min() ? false :
356 template <typename RHS, RHS rhs, typename LHS>
357 bool greater_than_impl(LHS const lhs) {
359 rhs > std::numeric_limits<LHS>::max() ? false :
360 rhs < std::numeric_limits<LHS>::min() ? true :
364 #pragma GCC diagnostic pop
366 } // namespace detail {
369 template <typename T>
370 constexpr bool is_negative(T x) {
371 return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
375 template <typename T>
376 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
379 template <typename T>
380 constexpr bool is_positive(T x) { return !is_non_positive(x); }
383 template <typename T>
384 constexpr bool is_non_negative(T x) {
385 return !x || is_positive(x);
388 template <typename RHS, RHS rhs, typename LHS>
389 bool less_than(LHS const lhs) {
390 return detail::less_than_impl<
391 RHS, rhs, typename std::remove_reference<LHS>::type
395 template <typename RHS, RHS rhs, typename LHS>
396 bool greater_than(LHS const lhs) {
397 return detail::greater_than_impl<
398 RHS, rhs, typename std::remove_reference<LHS>::type
403 * Like std::piecewise_construct, a tag type & instance used for in-place
404 * construction of non-movable contained types, e.g. by Synchronized.
406 struct construct_in_place_t {};
407 constexpr construct_in_place_t construct_in_place{};
411 // gcc-5.0 changed string's implementation in libgcc to be non-relocatable
413 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string);
415 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector);
416 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list);
417 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque);
418 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr);
419 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr);
420 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function);
423 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(boost::shared_ptr);
425 #define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name) \
426 template <typename T> \
428 template <typename C> \
429 constexpr static bool test(typename C::type_name*) { return true; } \
430 template <typename> \
431 constexpr static bool test(...) { return false; } \
432 constexpr static bool value = test<T>(nullptr); \
435 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
436 template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
437 class classname<TTheClass_, RTheReturn_(TTheArgs_...) cv_qual> { \
439 typename UTheClass_, RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual \
440 > struct sfinae {}; \
441 template <typename UTheClass_> \
442 constexpr static bool test(sfinae<UTheClass_, &UTheClass_::func_name>*) \
444 template <typename> \
445 constexpr static bool test(...) { return false; } \
447 constexpr static bool value = test<TTheClass_>(nullptr); \
451 * The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
452 * classes that check for the existence of a member function with
453 * a given name and signature. It currently does not support
454 * checking for inherited members.
456 * Such classes receive two template parameters: the class to be checked
457 * and the signature of the member function. A static boolean field
458 * named `value` (which is also constexpr) tells whether such member
461 * Each traits class created is bound only to the member name, not to
462 * its signature nor to the type of the class containing it.
464 * Say you need to know if a given class has a member function named
465 * `test` with the following signature:
469 * You'd need this macro to create a traits class to check for a member
470 * named `test`, and then use this traits class to check for the signature:
474 * FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
476 * } // unnamed-namespace
479 * cout << "Does class Foo have a member int test() const? "
480 * << boolalpha << has_test_traits<Foo, int() const>::value;
483 * You can use the same traits class to test for a completely different
484 * signature, on a completely different class, as long as the member name
488 * cout << "Does class Foo have a member int test()? "
489 * << boolalpha << has_test_traits<Foo, int()>::value;
490 * cout << "Does class Foo have a member int test() const? "
491 * << boolalpha << has_test_traits<Foo, int() const>::value;
492 * cout << "Does class Bar have a member double test(const string&, long)? "
493 * << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
496 * @author: Marcelo Juchem <marcelo@fb.com>
498 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name) \
499 template <typename, typename> class classname; \
500 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, ); \
501 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const); \
502 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
503 classname, func_name, /* nolint */ volatile); \
504 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
505 classname, func_name, /* nolint */ volatile const)