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/*
* Copyright 2015 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// @author: Andrei Alexandrescu
#ifndef FOLLY_BASE_TRAITS_H_
#define FOLLY_BASE_TRAITS_H_
#include <memory>
#include <limits>
#include <type_traits>
#include <functional>
#include <folly/Portability.h>
// libc++ doesn't provide this header, nor does msvc
#ifdef FOLLY_HAVE_BITS_CXXCONFIG_H
// This file appears in two locations: inside fbcode and in the
// libstdc++ source code (when embedding fbstring as std::string).
// To aid in this schizophrenic use, two macros are defined in
// c++config.h:
// _LIBSTDCXX_FBSTRING - Set inside libstdc++. This is useful to
// gate use inside fbcode v. libstdc++
#include <bits/c++config.h>
#endif
#include <boost/type_traits.hpp>
#include <boost/mpl/and.hpp>
#include <boost/mpl/has_xxx.hpp>
#include <boost/mpl/not.hpp>
namespace folly {
/**
* IsRelocatable<T>::value describes the ability of moving around
* memory a value of type T by using memcpy (as opposed to the
* conservative approach of calling the copy constructor and then
* destroying the old temporary. Essentially for a relocatable type,
* the following two sequences of code should be semantically
* equivalent:
*
* void move1(T * from, T * to) {
* new(to) T(from);
* (*from).~T();
* }
*
* void move2(T * from, T * to) {
* memcpy(to, from, sizeof(T));
* }
*
* Most C++ types are relocatable; the ones that aren't would include
* internal pointers or (very rarely) would need to update remote
* pointers to pointers tracking them. All C++ primitive types and
* type constructors are relocatable.
*
* This property can be used in a variety of optimizations. Currently
* fbvector uses this property intensively.
*
* The default conservatively assumes the type is not
* relocatable. Several specializations are defined for known
* types. You may want to add your own specializations. Do so in
* namespace folly and make sure you keep the specialization of
* IsRelocatable<SomeStruct> in the same header as SomeStruct.
*
* You may also declare a type to be relocatable by including
* `typedef std::true_type IsRelocatable;`
* in the class header.
*
* It may be unset in a base class by overriding the typedef to false_type.
*/
/*
* IsTriviallyCopyable describes the value semantics property. C++11 contains
* the type trait is_trivially_copyable; however, it is not yet implemented
* in gcc (as of 4.7.1), and the user may wish to specify otherwise.
*/
/*
* IsZeroInitializable describes the property that default construction is the
* same as memset(dst, 0, sizeof(T)).
*/
namespace traits_detail {
#define FOLLY_HAS_TRUE_XXX(name) \
BOOST_MPL_HAS_XXX_TRAIT_DEF(name); \
template <class T> struct name ## _is_true \
: std::is_same<typename T::name, std::true_type> {}; \
template <class T> struct has_true_ ## name \
: std::conditional< \
has_ ## name <T>::value, \
name ## _is_true<T>, \
std::false_type \
>:: type {};
FOLLY_HAS_TRUE_XXX(IsRelocatable)
FOLLY_HAS_TRUE_XXX(IsZeroInitializable)
FOLLY_HAS_TRUE_XXX(IsTriviallyCopyable)
#undef FOLLY_HAS_TRUE_XXX
}
template <class T> struct IsTriviallyCopyable
: std::integral_constant<bool,
!std::is_class<T>::value ||
// TODO: add alternate clause is_trivially_copyable, when available
traits_detail::has_true_IsTriviallyCopyable<T>::value
> {};
template <class T> struct IsRelocatable
: std::integral_constant<bool,
!std::is_class<T>::value ||
// TODO add this line (and some tests for it) when we upgrade to gcc 4.7
//std::is_trivially_move_constructible<T>::value ||
IsTriviallyCopyable<T>::value ||
traits_detail::has_true_IsRelocatable<T>::value
> {};
template <class T> struct IsZeroInitializable
: std::integral_constant<bool,
!std::is_class<T>::value ||
traits_detail::has_true_IsZeroInitializable<T>::value
> {};
} // namespace folly
/**
* Use this macro ONLY inside namespace folly. When using it with a
* regular type, use it like this:
*
* // Make sure you're at namespace ::folly scope
* template<> FOLLY_ASSUME_RELOCATABLE(MyType)
*
* When using it with a template type, use it like this:
*
* // Make sure you're at namespace ::folly scope
* template<class T1, class T2>
* FOLLY_ASSUME_RELOCATABLE(MyType<T1, T2>)
*/
#define FOLLY_ASSUME_RELOCATABLE(...) \
struct IsRelocatable< __VA_ARGS__ > : std::true_type {};
/**
* Use this macro ONLY inside namespace boost. When using it with a
* regular type, use it like this:
*
* // Make sure you're at namespace ::boost scope
* template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType)
*
* When using it with a template type, use it like this:
*
* // Make sure you're at namespace ::boost scope
* template<class T1, class T2>
* FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(MyType<T1, T2>)
*/
#define FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(...) \
struct has_nothrow_constructor< __VA_ARGS__ > : ::boost::true_type {};
/**
* The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode two
* assumptions: first, that the type is relocatable per IsRelocatable
* above, and that it has a nothrow constructor. Most types can be
* assumed to satisfy both conditions, but it is the responsibility of
* the user to state that assumption. User-defined classes will not
* work with fbvector (see FBVector.h) unless they state this
* combination of properties.
*
* Use FOLLY_ASSUME_FBVECTOR_COMPATIBLE with regular types like this:
*
* FOLLY_ASSUME_FBVECTOR_COMPATIBLE(MyType)
*
* The versions FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1, _2, _3, and _4
* allow using the macro for describing templatized classes with 1, 2,
* 3, and 4 template parameters respectively. For template classes
* just use the macro with the appropriate number and pass the name of
* the template to it. Example:
*
* template <class T1, class T2> class MyType { ... };
* ...
* // Make sure you're at global scope
* FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(MyType)
*/
// Use this macro ONLY at global level (no namespace)
#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE(...) \
namespace folly { template<> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__) } \
namespace boost { \
template<> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__) }
// Use this macro ONLY at global level (no namespace)
#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(...) \
namespace folly { \
template <class T1> FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1>) } \
namespace boost { \
template <class T1> FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1>) }
// Use this macro ONLY at global level (no namespace)
#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(...) \
namespace folly { \
template <class T1, class T2> \
FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2>) } \
namespace boost { \
template <class T1, class T2> \
FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2>) }
// Use this macro ONLY at global level (no namespace)
#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(...) \
namespace folly { \
template <class T1, class T2, class T3> \
FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3>) } \
namespace boost { \
template <class T1, class T2, class T3> \
FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3>) }
// Use this macro ONLY at global level (no namespace)
#define FOLLY_ASSUME_FBVECTOR_COMPATIBLE_4(...) \
namespace folly { \
template <class T1, class T2, class T3, class T4> \
FOLLY_ASSUME_RELOCATABLE(__VA_ARGS__<T1, T2, T3, T4>) } \
namespace boost { \
template <class T1, class T2, class T3, class T4> \
FOLLY_ASSUME_HAS_NOTHROW_CONSTRUCTOR(__VA_ARGS__<T1, T2, T3, T4>) }
/**
* Instantiate FOLLY_ASSUME_FBVECTOR_COMPATIBLE for a few types. It is
* safe to assume that pair is compatible if both of its components
* are. Furthermore, all STL containers can be assumed to comply,
* although that is not guaranteed by the standard.
*/
FOLLY_NAMESPACE_STD_BEGIN
template <class T, class U>
struct pair;
#ifndef _GLIBCXX_USE_FB
template <class T, class R, class A>
class basic_string;
#else
template <class T, class R, class A, class S>
class basic_string;
#endif
template <class T, class A>
class vector;
template <class T, class A>
class deque;
template <class T, class A>
class list;
template <class T, class C, class A>
class set;
template <class K, class V, class C, class A>
class map;
template <class T>
class shared_ptr;
FOLLY_NAMESPACE_STD_END
namespace boost {
template <class T> class shared_ptr;
template <class T, class U>
struct has_nothrow_constructor< std::pair<T, U> >
: ::boost::mpl::and_< has_nothrow_constructor<T>,
has_nothrow_constructor<U> > {};
} // namespace boost
namespace folly {
// STL commonly-used types
template <class T, class U>
struct IsRelocatable< std::pair<T, U> >
: ::boost::mpl::and_< IsRelocatable<T>, IsRelocatable<U> > {};
// Is T one of T1, T2, ..., Tn?
template <class T, class... Ts>
struct IsOneOf {
enum { value = false };
};
template <class T, class T1, class... Ts>
struct IsOneOf<T, T1, Ts...> {
enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
};
/*
* Complementary type traits for integral comparisons.
*
* For instance, `if(x < 0)` yields an error in clang for unsigned types
* when -Werror is used due to -Wtautological-compare
*
*
* @author: Marcelo Juchem <marcelo@fb.com>
*/
namespace detail {
template <typename T, bool>
struct is_negative_impl {
constexpr static bool check(T x) { return x < 0; }
};
template <typename T>
struct is_negative_impl<T, false> {
constexpr static bool check(T) { return false; }
};
// folly::to integral specializations can end up generating code
// inside what are really static ifs (not executed because of the templated
// types) that violate -Wsign-compare so suppress them in order to not prevent
// all calling code from using it.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wsign-compare"
template <typename RHS, RHS rhs, typename LHS>
bool less_than_impl(
typename std::enable_if<
(rhs <= std::numeric_limits<LHS>::max()
&& rhs > std::numeric_limits<LHS>::min()),
LHS
>::type const lhs
) {
return lhs < rhs;
}
template <typename RHS, RHS rhs, typename LHS>
bool less_than_impl(
typename std::enable_if<
(rhs > std::numeric_limits<LHS>::max()),
LHS
>::type const
) {
return true;
}
template <typename RHS, RHS rhs, typename LHS>
bool less_than_impl(
typename std::enable_if<
(rhs <= std::numeric_limits<LHS>::min()),
LHS
>::type const
) {
return false;
}
#pragma GCC diagnostic pop
template <typename RHS, RHS rhs, typename LHS>
bool greater_than_impl(
typename std::enable_if<
(rhs <= std::numeric_limits<LHS>::max()
&& rhs >= std::numeric_limits<LHS>::min()),
LHS
>::type const lhs
) {
return lhs > rhs;
}
template <typename RHS, RHS rhs, typename LHS>
bool greater_than_impl(
typename std::enable_if<
(rhs > std::numeric_limits<LHS>::max()),
LHS
>::type const
) {
return false;
}
template <typename RHS, RHS rhs, typename LHS>
bool greater_than_impl(
typename std::enable_if<
(rhs < std::numeric_limits<LHS>::min()),
LHS
>::type const
) {
return true;
}
} // namespace detail {
// same as `x < 0`
template <typename T>
constexpr bool is_negative(T x) {
return folly::detail::is_negative_impl<T, std::is_signed<T>::value>::check(x);
}
// same as `x <= 0`
template <typename T>
constexpr bool is_non_positive(T x) { return !x || folly::is_negative(x); }
// same as `x > 0`
template <typename T>
constexpr bool is_positive(T x) { return !is_non_positive(x); }
// same as `x >= 0`
template <typename T>
constexpr bool is_non_negative(T x) {
return !x || is_positive(x);
}
template <typename RHS, RHS rhs, typename LHS>
bool less_than(LHS const lhs) {
return detail::less_than_impl<
RHS, rhs, typename std::remove_reference<LHS>::type
>(lhs);
}
template <typename RHS, RHS rhs, typename LHS>
bool greater_than(LHS const lhs) {
return detail::greater_than_impl<
RHS, rhs, typename std::remove_reference<LHS>::type
>(lhs);
}
} // namespace folly
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_3(std::basic_string);
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::vector);
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::list);
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::deque);
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr);
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr);
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::function);
// Boost
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(boost::shared_ptr);
#define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name) \
template <typename T> \
struct classname { \
template <typename C> \
constexpr static bool test(typename C::type_name*) { return true; } \
template <typename> \
constexpr static bool test(...) { return false; } \
constexpr static bool value = test<T>(nullptr); \
}
#define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
class classname<TTheClass_, RTheReturn_(TTheArgs_...) cv_qual> { \
template < \
typename UTheClass_, RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual \
> struct sfinae {}; \
template <typename UTheClass_> \
constexpr static bool test(sfinae<UTheClass_, &UTheClass_::func_name>*) \
{ return true; } \
template <typename> \
constexpr static bool test(...) { return false; } \
public: \
constexpr static bool value = test<TTheClass_>(nullptr); \
}
/*
* The FOLLY_CREATE_HAS_MEMBER_FN_TRAITS is used to create traits
* classes that check for the existence of a member function with
* a given name and signature. It currently does not support
* checking for inherited members.
*
* Such classes receive two template parameters: the class to be checked
* and the signature of the member function. A static boolean field
* named `value` (which is also constexpr) tells whether such member
* function exists.
*
* Each traits class created is bound only to the member name, not to
* its signature nor to the type of the class containing it.
*
* Say you need to know if a given class has a member function named
* `test` with the following signature:
*
* int test() const;
*
* You'd need this macro to create a traits class to check for a member
* named `test`, and then use this traits class to check for the signature:
*
* namespace {
*
* FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(has_test_traits, test);
*
* } // unnamed-namespace
*
* void some_func() {
* cout << "Does class Foo have a member int test() const? "
* << boolalpha << has_test_traits<Foo, int() const>::value;
* }
*
* You can use the same traits class to test for a completely different
* signature, on a completely different class, as long as the member name
* is the same:
*
* void some_func() {
* cout << "Does class Foo have a member int test()? "
* << boolalpha << has_test_traits<Foo, int()>::value;
* cout << "Does class Foo have a member int test() const? "
* << boolalpha << has_test_traits<Foo, int() const>::value;
* cout << "Does class Bar have a member double test(const string&, long)? "
* << boolalpha << has_test_traits<Bar, double(const string&, long)>::value;
* }
*
* @author: Marcelo Juchem <marcelo@fb.com>
*/
#define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS(classname, func_name) \
template <typename, typename> class classname; \
FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, ); \
FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, const); \
FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
classname, func_name, /* nolint */ volatile); \
FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL( \
classname, func_name, /* nolint */ volatile const)
#endif //FOLLY_BASE_TRAITS_H_