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/and.hpp>
41 #include <boost/mpl/has_xxx.hpp>
42 #include <boost/mpl/not.hpp>
47 * IsRelocatable<T>::value describes the ability of moving around
48 * memory a value of type T by using memcpy (as opposed to the
49 * conservative approach of calling the copy constructor and then
50 * destroying the old temporary. Essentially for a relocatable type,
51 * the following two sequences of code should be semantically
54 * void move1(T * from, T * to) {
59 * void move2(T * from, T * to) {
60 * memcpy(to, from, sizeof(T));
63 * Most C++ types are relocatable; the ones that aren't would include
64 * internal pointers or (very rarely) would need to update remote
65 * pointers to pointers tracking them. All C++ primitive types and
66 * type constructors are relocatable.
68 * This property can be used in a variety of optimizations. Currently
69 * fbvector uses this property intensively.
71 * The default conservatively assumes the type is not
72 * relocatable. Several specializations are defined for known
73 * types. You may want to add your own specializations. Do so in
74 * namespace folly and make sure you keep the specialization of
75 * IsRelocatable<SomeStruct> in the same header as SomeStruct.
77 * You may also declare a type to be relocatable by including
78 * `typedef std::true_type IsRelocatable;`
79 * in the class header.
81 * It may be unset in a base class by overriding the typedef to false_type.
84 * IsTriviallyCopyable describes the value semantics property. C++11 contains
85 * the type trait is_trivially_copyable; however, it is not yet implemented
86 * in gcc (as of 4.7.1), and the user may wish to specify otherwise.
89 * IsZeroInitializable describes the property that default construction is the
90 * same as memset(dst, 0, sizeof(T)).
93 namespace traits_detail {
95 #define FOLLY_HAS_TRUE_XXX(name) \
96 BOOST_MPL_HAS_XXX_TRAIT_DEF(name); \
97 template <class T> struct name ## _is_true \
98 : std::is_same<typename T::name, std::true_type> {}; \
99 template <class T> struct has_true_ ## name \
100 : std::conditional< \
101 has_ ## name <T>::value, \
102 name ## _is_true<T>, \
106 FOLLY_HAS_TRUE_XXX(IsRelocatable)
107 FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
108 FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
110 #undef FOLLY_HAS_TRUE_XXX
113 template <class T> struct IsTriviallyCopyable
114 : std::integral_constant<bool,
115 !std::is_class<T>::value ||
116 // TODO: add alternate clause is_trivially_copyable, when available
117 traits_detail::has_true_IsTriviallyCopyable<T>::value
120 template <class T> struct IsRelocatable
121 : std::integral_constant<bool,
122 !std::is_class<T>::value ||
123 // TODO add this line (and some tests for it) when we upgrade to gcc 4.7
124 //std::is_trivially_move_constructible<T>::value ||
125 IsTriviallyCopyable<T>::value ||
126 traits_detail::has_true_IsRelocatable<T>::value
129 template <class T> struct IsZeroInitializable
130 : std::integral_constant<bool,
131 !std::is_class<T>::value ||
132 traits_detail::has_true_IsZeroInitializable<T>::value
135 template <typename...>
136 struct Conjunction : std::true_type {};
137 template <typename T>
138 struct Conjunction<T> : T {};
139 template <typename T, typename... TList>
140 struct Conjunction<T, TList...>
141 : std::conditional<T::value, Conjunction<TList...>, T>::type {};
143 template <typename...>
144 struct Disjunction : std::false_type {};
145 template <typename T>
146 struct Disjunction<T> : T {};
147 template <typename T, typename... TList>
148 struct Disjunction<T, TList...>
149 : std::conditional<T::value, T, Disjunction<TList...>>::type {};
151 template <typename T>
152 struct Negation : std::integral_constant<bool, !T::value> {};
157 * Use this macro ONLY inside namespace folly. When using it with a
158 * regular type, use it like this:
160 * // Make sure you're at namespace ::folly scope
161 * template<> FOLLY_ASSUME_RELOCATABLE(MyType)
163 * When using it with a template type, use it like this:
165 * // Make sure you're at namespace ::folly scope
166 * template<class T1, class T2>
167 * FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
169 #define FOLLY_ASSUME_RELOCATABLE(...) \
170 struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
173 * Use this macro ONLY inside namespace boost. When using it with a
174 * regular type, use it like this:
176 * // Make sure you're at namespace ::boost scope
177 * template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType)
179 * When using it with a template type, use it like this:
181 * // Make sure you're at namespace ::boost scope
182 * template<class T1, class T2>
183 * FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType<T1, T2>)
185 #define FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(...) \
186 struct has_nothrow_constructor< __VA_ARGS__ > : ::boost::true_type {};
189 * The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode two
190 * assumptions: first, that the type is relocatable per IsRelocatable
191 * above, and that it has a nothrow constructor. Most types can be
192 * assumed to satisfy both conditions, but it is the responsibility of
193 * the user to state that assumption. User-defined classes will not
194 * work with fbvector (see FBVector.h) unless they state this
195 * combination of properties.
197 * Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
199 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
201 * The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
202 * allow using the macro for describing templatized classes with 1, 2,
203 * 3, and 4 template parameters respectively. For template classes
204 * just use the macro with the appropriate number and pass the name of
205 * the template to it. Example:
207 * template <class T1, class T2> class MyType { ... };
209 * // Make sure you're at global scope
210 * FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
213 // Use this macro ONLY at global level (no namespace)
214 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
215 namespace folly { template<> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) } \
217 template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__) }
218 // Use this macro ONLY at global level (no namespace)
219 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
221 template <class T1> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) } \
223 template <class T1> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1>) }
224 // Use this macro ONLY at global level (no namespace)
225 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
227 template <class T1, class T2> \
228 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) } \
230 template <class T1, class T2> \
231 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2>) }
232 // Use this macro ONLY at global level (no namespace)
233 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
235 template <class T1, class T2, class T3> \
236 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) } \
238 template <class T1, class T2, class T3> \
239 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3>) }
240 // Use this macro ONLY at global level (no namespace)
241 #define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
243 template <class T1, class T2, class T3, class T4> \
244 FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) } \
246 template <class T1, class T2, class T3, class T4> \
247 FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3, T4>) }
250 * Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
251 * safe to assume that pair is compatible if both of its components
252 * are. Furthermore, all STL containers can be assumed to comply,
253 * although that is not guaranteed by the standard.
256 FOLLY_NAMESPACE_STD_BEGIN
258 template <class T, class U>
260 #ifndef _GLIBCXX_USE_FB
261 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
262 template <class T, class R, class A>
264 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
266 template <class T, class R, class A, class S>
269 template <class T, class A>
271 template <class T, class A>
273 FOLLY_GLIBCXX_NAMESPACE_CXX11_BEGIN
274 template <class T, class A>
276 FOLLY_GLIBCXX_NAMESPACE_CXX11_END
277 template <class T, class C, class A>
279 template <class K, class V, class C, class A>
284 FOLLY_NAMESPACE_STD_END
288 template <class T> class shared_ptr;
290 template <class T, class U>
291 struct has_nothrow_constructor< std::pair<T, U> >
292 : ::boost::mpl::and_< has_nothrow_constructor<T>,
293 has_nothrow_constructor<U> > {};
299 // STL commonly-used types
300 template <class T, class U>
301 struct IsRelocatable< std::pair<T, U> >
302 : ::boost::mpl::and_< IsRelocatable<T>, IsRelocatable<U> > {};
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 so suppress them in order to not prevent
340 // all calling code from using it.
341 #pragma GCC diagnostic push
342 #pragma GCC diagnostic ignored "-Wsign-compare"
344 template <typename RHS, RHS rhs, typename LHS>
345 bool less_than_impl(LHS const lhs) {
347 rhs > std::numeric_limits<LHS>::max() ? true :
348 rhs <= std::numeric_limits<LHS>::min() ? false :
352 #pragma GCC diagnostic pop
354 template <typename RHS, RHS rhs, typename LHS>
355 bool greater_than_impl(LHS const lhs) {
357 rhs > std::numeric_limits<LHS>::max() ? false :
358 rhs < std::numeric_limits<LHS>::min() ? true :
362 } // namespace detail {
365 template <typename T>
366 constexpr bool is_negative(T x) {
367 return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
371 template <typename T>
372 constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
375 template <typename T>
376 constexpr bool is_positive(T x) { return !is_non_positive(x); }
379 template <typename T>
380 constexpr bool is_non_negative(T x) {
381 return !x || is_positive(x);
384 template <typename RHS, RHS rhs, typename LHS>
385 bool less_than(LHS const lhs) {
386 return detail::less_than_impl<
387 RHS, rhs, typename std::remove_reference<LHS>::type
391 template <typename RHS, RHS rhs, typename LHS>
392 bool greater_than(LHS const lhs) {
393 return detail::greater_than_impl<
394 RHS, rhs, typename std::remove_reference<LHS>::type
399 * Like std::piecewise_construct, a tag type & instance used for in-place
400 * construction of non-movable contained types, e.g. by Synchronized.
402 struct construct_in_place_t {};
403 constexpr construct_in_place_t construct_in_place{};
407 // gcc-5.0 changed string's implementation in libgcc to be non-relocatable
409 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string);
411 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector);
412 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list);
413 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque);
414 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr);
415 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr);
416 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function);
419 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(boost::shared_ptr);
421 #define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name) \
422 template <typename T> \
424 template <typename C> \
425 constexpr static bool test(typename C::type_name*) { return true; } \
426 template <typename> \
427 constexpr static bool test(...) { return false; } \
428 constexpr static bool value = test<T>(nullptr); \
431 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
432 template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
433 class classname<TTheClass_, RTheReturn_(TTheArgs_...) cv_qual> { \
435 typename UTheClass_, RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual \
436 > struct sfinae {}; \
437 template <typename UTheClass_> \
438 constexpr static bool test(sfinae<UTheClass_, &UTheClass_::func_name>*) \
440 template <typename> \
441 constexpr static bool test(...) { return false; } \
443 constexpr static bool value = test<TTheClass_>(nullptr); \
447 * The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
448 * classes that check for the existence of a member function with
449 * a given name and signature. It currently does not support
450 * checking for inherited members.
452 * Such classes receive two template parameters: the class to be checked
453 * and the signature of the member function. A static boolean field
454 * named `value` (which is also constexpr) tells whether such member
457 * Each traits class created is bound only to the member name, not to
458 * its signature nor to the type of the class containing it.
460 * Say you need to know if a given class has a member function named
461 * `test` with the following signature:
465 * You'd need this macro to create a traits class to check for a member
466 * named `test`, and then use this traits class to check for the signature:
470 * FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
472 * } // unnamed-namespace
475 * cout << "Does class Foo have a member int test() const? "
476 * << boolalpha << has_test_traits<Foo, int() const>::value;
479 * You can use the same traits class to test for a completely different
480 * signature, on a completely different class, as long as the member name
484 * cout << "Does class Foo have a member int test()? "
485 * << boolalpha << has_test_traits<Foo, int()>::value;
486 * cout << "Does class Foo have a member int test() const? "
487 * << boolalpha << has_test_traits<Foo, int() const>::value;
488 * cout << "Does class Bar have a member double test(const string&, long)? "
489 * << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
492 * @author: Marcelo Juchem <marcelo@fb.com>
494 #define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name) \
495 template <typename, typename> class classname; \
496 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, ); \
497 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const); \
498 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
499 classname, func_name, /* nolint */ volatile); \
500 FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
501 classname, func_name, /* nolint */ volatile const)