/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* 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
#pragma once
#include <functional>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <folly/Portability.h>
#define FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(classname, type_name) \
template <typename TTheClass_> \
struct classname##__folly_traits_impl__ { \
template <typename UTheClass_> \
static constexpr bool test(typename UTheClass_::type_name*) { \
return true; \
} \
template <typename> \
static constexpr bool test(...) { \
return false; \
} \
}; \
template <typename TTheClass_> \
using classname = typename std::conditional< \
classname##__folly_traits_impl__<TTheClass_>::template test<TTheClass_>( \
nullptr), \
std::true_type, \
std::false_type>::type
#define FOLLY_CREATE_HAS_MEMBER_FN_TRAITS_IMPL(classname, func_name, cv_qual) \
template <typename TTheClass_, typename RTheReturn_, typename... TTheArgs_> \
struct classname##__folly_traits_impl__< \
TTheClass_, \
RTheReturn_(TTheArgs_...) cv_qual> { \
template < \
typename UTheClass_, \
RTheReturn_ (UTheClass_::*)(TTheArgs_...) cv_qual> \
struct sfinae {}; \
template <typename UTheClass_> \
static std::true_type test(sfinae<UTheClass_, &UTheClass_::func_name>*); \
template <typename> \
static std::false_type test(...); \
}
/*
* 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> \
struct classname##__folly_traits_impl__; \
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); \
template <typename TTheClass_, typename TTheSignature_> \
using classname = \
decltype(classname##__folly_traits_impl__<TTheClass_, TTheSignature_>:: \
template test<TTheClass_>(nullptr))
namespace folly {
template <typename...>
struct tag_t {};
#if __cplusplus >= 201703L
template <typename... T>
inline constexpr tag_t<T...> tag;
#endif
#if __cpp_lib_bool_constant || _MSC_VER
using std::bool_constant;
#else
// mimic: std::bool_constant, C++17
template <bool B>
using bool_constant = std::integral_constant<bool, B>;
#endif
template <std::size_t I>
using index_constant = std::integral_constant<std::size_t, I>;
namespace detail {
/**
* A type trait to check if a given type is an instantiation of a class
* template.
*
* Note that this only works with template type parameters. It does not work
* with non-type template parameters, template template parameters, or alias
* templates.
*/
template <template <typename...> class, typename>
struct is_instantiation_of : std::false_type {};
template <template <typename...> class C, typename... T>
struct is_instantiation_of<C, C<T...>> : std::true_type {};
template <template <typename...> class C, typename T>
constexpr bool is_instantiation_of_v = is_instantiation_of<C, T>::value;
} // namespace detail
namespace detail {
template <bool, typename T>
struct is_constexpr_default_constructible_;
template <typename T>
struct is_constexpr_default_constructible_<false, T> {
using type = std::false_type;
};
template <typename T>
struct is_constexpr_default_constructible_<true, T> {
static constexpr int take(T) {
return 0;
}
template <int = take(T{})>
static std::true_type sfinae(int);
static std::false_type sfinae(...);
using type = decltype(sfinae(0));
};
} // namespace detail
// is_constexpr_default_constructible
// is_constexpr_default_constructible_v
//
// A type trait, with associated variable template, which determines whether
// its type parameter is constexpr default-constructible, that is, default-
// constructible in a constexpr context.
//
// Instantiations of is_constexpr_default_constructible unambiguously inherit
// std::integral_constant<bool, V> for some bool V.
template <typename T>
struct is_constexpr_default_constructible
: detail::is_constexpr_default_constructible_<
std::is_default_constructible<T>::value,
T>::type {};
template <typename T>
FOLLY_INLINE_VARIABLE constexpr bool is_constexpr_default_constructible_v =
is_constexpr_default_constructible<T>::value;
/***
* _t
*
* Instead of:
*
* using decayed = typename std::decay<T>::type;
*
* With the C++14 standard trait aliases, we could use:
*
* using decayed = std::decay_t<T>;
*
* Without them, we could use:
*
* using decayed = _t<std::decay<T>>;
*
* Also useful for any other library with template types having dependent
* member types named `type`, like the standard trait types.
*/
template <typename T>
using _t = typename T::type;
/**
* A type trait to remove all const volatile and reference qualifiers on a
* type T
*/
template <typename T>
struct remove_cvref {
using type =
typename std::remove_cv<typename std::remove_reference<T>::type>::type;
};
template <typename T>
using remove_cvref_t = typename remove_cvref<T>::type;
namespace detail {
template <typename Src>
struct like_ {
template <typename Dst>
using apply = Dst;
};
template <typename Src>
struct like_<Src const> {
template <typename Dst>
using apply = Dst const;
};
template <typename Src>
struct like_<Src volatile> {
template <typename Dst>
using apply = Dst volatile;
};
template <typename Src>
struct like_<Src const volatile> {
template <typename Dst>
using apply = Dst const volatile;
};
template <typename Src>
struct like_<Src&> {
template <typename Dst>
using apply = typename like_<Src>::template apply<Dst>&;
};
template <typename Src>
struct like_<Src&&> {
template <typename Dst>
using apply = typename like_<Src>::template apply<Dst>&&;
};
} // namespace detail
// mimic: like_t, p0847r0
template <typename Src, typename Dst>
using like_t = typename detail::like_<Src>::template apply<remove_cvref_t<Dst>>;
// mimic: like, p0847r0
template <typename Src, typename Dst>
struct like {
using type = like_t<Src, Dst>;
};
/**
* type_t
*
* A type alias for the first template type argument. `type_t` is useful for
* controlling class-template and function-template partial specialization.
*
* Example:
*
* template <typename Value>
* class Container {
* public:
* template <typename... Args>
* Container(
* type_t<in_place_t, decltype(Value(std::declval<Args>()...))>,
* Args&&...);
* };
*
* void_t
*
* A type alias for `void`. `void_t` is useful for controling class-template
* and function-template partial specialization.
*
* Example:
*
* // has_value_type<T>::value is true if T has a nested type `value_type`
* template <class T, class = void>
* struct has_value_type
* : std::false_type {};
*
* template <class T>
* struct has_value_type<T, folly::void_t<typename T::value_type>>
* : std::true_type {};
*/
/**
* There is a bug in libstdc++, libc++, and MSVC's STL that causes it to
* ignore unused template parameter arguments in template aliases and does not
* cause substitution failures. This defect has been recorded here:
* http://open-std.org/JTC1/SC22/WG21/docs/cwg_defects.html#1558.
*
* This causes the implementation of std::void_t to be buggy, as it is likely
* defined as something like the following:
*
* template <typename...>
* using void_t = void;
*
* This causes the compiler to ignore all the template arguments and does not
* help when one wants to cause substitution failures. Rather declarations
* which have void_t in orthogonal specializations are treated as the same.
* For example, assuming the possible `T` types are only allowed to have
* either the alias `one` or `two` and never both or none:
*
* template <typename T,
* typename std::void_t<std::decay_t<T>::one>* = nullptr>
* void foo(T&&) {}
* template <typename T,
* typename std::void_t<std::decay_t<T>::two>* = nullptr>
* void foo(T&&) {}
*
* The second foo() will be a redefinition because it conflicts with the first
* one; void_t does not cause substitution failures - the template types are
* just ignored.
*/
namespace traits_detail {
template <class T, class...>
struct type_t_ {
using type = T;
};
} // namespace traits_detail
template <class T, class... Ts>
using type_t = typename traits_detail::type_t_<T, Ts...>::type;
template <class... Ts>
using void_t = type_t<void, Ts...>;
template <typename T>
using aligned_storage_for_t =
typename std::aligned_storage<sizeof(T), alignof(T)>::type;
// Older versions of libstdc++ do not provide std::is_trivially_copyable
#if defined(__clang__) && !defined(_LIBCPP_VERSION)
template <class T>
struct is_trivially_copyable : bool_constant<__is_trivially_copyable(T)> {};
#else
template <class T>
using is_trivially_copyable = std::is_trivially_copyable<T>;
#endif
template <class T>
FOLLY_INLINE_VARIABLE constexpr bool is_trivially_copyable_v =
is_trivially_copyable<T>::value;
/**
* 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.
*/
/*
* 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) \
FOLLY_CREATE_HAS_MEMBER_TYPE_TRAITS(has_##name, 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);
#undef FOLLY_HAS_TRUE_XXX
} // namespace traits_detail
struct Ignore {
Ignore() = default;
template <class T>
constexpr /* implicit */ Ignore(const T&) {}
template <class T>
const Ignore& operator=(T const&) const {
return *this;
}
};
template <class...>
using Ignored = Ignore;
namespace traits_detail_IsEqualityComparable {
Ignore operator==(Ignore, Ignore);
template <class T, class U = T>
struct IsEqualityComparable
: std::is_convertible<
decltype(std::declval<T>() == std::declval<U>()),
bool> {};
} // namespace traits_detail_IsEqualityComparable
/* using override */ using traits_detail_IsEqualityComparable::
IsEqualityComparable;
namespace traits_detail_IsLessThanComparable {
Ignore operator<(Ignore, Ignore);
template <class T, class U = T>
struct IsLessThanComparable
: std::is_convertible<
decltype(std::declval<T>() < std::declval<U>()),
bool> {};
} // namespace traits_detail_IsLessThanComparable
/* using override */ using traits_detail_IsLessThanComparable::
IsLessThanComparable;
namespace traits_detail_IsNothrowSwappable {
#if defined(__cpp_lib_is_swappable) || (_CPPLIB_VER && _HAS_CXX17)
// MSVC already implements the C++17 P0185R1 proposal which adds
// std::is_nothrow_swappable, so use it instead if C++17 mode is
// enabled.
template <typename T>
using IsNothrowSwappable = std::is_nothrow_swappable<T>;
#elif _CPPLIB_VER
// MSVC defines the base even if C++17 is disabled, and MSVC has
// issues with our fallback implementation due to over-eager
// evaluation of noexcept.
template <typename T>
using IsNothrowSwappable = std::_Is_nothrow_swappable<T>;
#else
/* using override */ using std::swap;
template <class T>
struct IsNothrowSwappable
: bool_constant<std::is_nothrow_move_constructible<T>::value&& noexcept(
swap(std::declval<T&>(), std::declval<T&>()))> {};
#endif
} // namespace traits_detail_IsNothrowSwappable
/* using override */ using traits_detail_IsNothrowSwappable::IsNothrowSwappable;
template <class T>
struct IsRelocatable : std::conditional<
traits_detail::has_IsRelocatable<T>::value,
traits_detail::has_true_IsRelocatable<T>,
// TODO add this line (and some tests for it) when we
// upgrade to gcc 4.7
// std::is_trivially_move_constructible<T>::value ||
is_trivially_copyable<T>>::type {};
template <class T>
struct IsZeroInitializable
: std::conditional<
traits_detail::has_IsZeroInitializable<T>::value,
traits_detail::has_true_IsZeroInitializable<T>,
bool_constant<!std::is_class<T>::value>>::type {};
namespace detail {
template <bool>
struct conditional_;
template <>
struct conditional_<false> {
template <typename, typename T>
using apply = T;
};
template <>
struct conditional_<true> {
template <typename T, typename>
using apply = T;
};
} // namespace detail
// conditional_t
//
// Like std::conditional_t but with only two total class template instances,
// rather than as many class template instances as there are uses.
//
// As one effect, the result can be used in deducible contexts, allowing
// deduction of conditional_t<V, T, F> to work when T or F is a template param.
template <bool V, typename T, typename F>
using conditional_t = typename detail::conditional_<V>::template apply<T, F>;
template <typename...>
struct Conjunction : std::true_type {};
template <typename T>
struct Conjunction<T> : T {};
template <typename T, typename... TList>
struct Conjunction<T, TList...>
: std::conditional<T::value, Conjunction<TList...>, T>::type {};
template <typename...>
struct Disjunction : std::false_type {};
template <typename T>
struct Disjunction<T> : T {};
template <typename T, typename... TList>
struct Disjunction<T, TList...>
: std::conditional<T::value, T, Disjunction<TList...>>::type {};
template <typename T>
struct Negation : bool_constant<!T::value> {};
template <bool... Bs>
struct Bools {
using valid_type = bool;
static constexpr std::size_t size() {
return sizeof...(Bs);
}
};
// Lighter-weight than Conjunction, but evaluates all sub-conditions eagerly.
template <class... Ts>
struct StrictConjunction
: std::is_same<Bools<Ts::value...>, Bools<(Ts::value || true)...>> {};
template <class... Ts>
struct StrictDisjunction
: Negation<
std::is_same<Bools<Ts::value...>, Bools<(Ts::value && false)...>>> {};
namespace detail {
template <typename, typename>
struct is_transparent_ : std::false_type {};
template <typename T>
struct is_transparent_<void_t<typename T::is_transparent>, T> : std::true_type {
};
} // namespace detail
// is_transparent
//
// To test whether a less, equal-to, or hash type follows the is-transparent
// protocol used by containers with optional heterogeneous access.
template <typename T>
struct is_transparent : detail::is_transparent_<void, T> {};
} // 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 {}
/**
* The FOLLY_ASSUME_FBVECTOR_COMPATIBLE* macros below encode the
* assumption that the type is relocatable per IsRelocatable
* above. Many types can be assumed to satisfy this condition, but
* it is the responsibility of the user to state that assumption.
* User-defined classes will not be optimized for use with
* fbvector (see FBVector.h) unless they state that assumption.
*
* 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__); \
}
// 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>); \
}
// 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>); \
}
// 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>); \
}
// 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 folly {
// STL commonly-used types
template <class T, class U>
struct IsRelocatable<std::pair<T, U>>
: bool_constant<IsRelocatable<T>::value && IsRelocatable<U>::value> {};
// Is T one of T1, T2, ..., Tn?
template <typename T, typename... Ts>
using IsOneOf = StrictDisjunction<std::is_same<T, Ts>...>;
/*
* 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 {
// 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 and/or -Wbool-compare so suppress them
// in order to not prevent all calling code from using it.
FOLLY_PUSH_WARNING
FOLLY_GNU_DISABLE_WARNING("-Wsign-compare")
FOLLY_GCC_DISABLE_WARNING("-Wbool-compare")
FOLLY_MSVC_DISABLE_WARNING(4287) // unsigned/negative constant mismatch
FOLLY_MSVC_DISABLE_WARNING(4388) // sign-compare
FOLLY_MSVC_DISABLE_WARNING(4804) // bool-compare
template <typename RHS, RHS rhs, typename LHS>
bool less_than_impl(LHS const lhs) {
// clang-format off
return
rhs > std::numeric_limits<LHS>::max() ? true :
rhs <= std::numeric_limits<LHS>::min() ? false :
lhs < rhs;
// clang-format on
}
template <typename RHS, RHS rhs, typename LHS>
bool greater_than_impl(LHS const lhs) {
// clang-format off
return
rhs > std::numeric_limits<LHS>::max() ? false :
rhs < std::numeric_limits<LHS>::min() ? true :
lhs > rhs;
// clang-format on
}
FOLLY_POP_WARNING
} // namespace detail
// same as `x < 0`
template <typename T>
constexpr bool is_negative(T x) {
return std::is_signed<T>::value && x < T(0);
}
// 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
// Assume nothing when compiling with MSVC.
#ifndef _MSC_VER
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_2(std::unique_ptr)
FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(std::shared_ptr)
#endif
/* Some combinations of compilers and C++ libraries make __int128 and
* unsigned __int128 available but do not correctly define their standard type
* traits.
*
* If FOLLY_SUPPLY_MISSING_INT128_TRAITS is defined, we define these traits
* here.
*
* @author: Phil Willoughby <philwill@fb.com>
*/
#if FOLLY_SUPPLY_MISSING_INT128_TRAITS
FOLLY_NAMESPACE_STD_BEGIN
template <>
struct is_arithmetic<__int128> : ::std::true_type {};
template <>
struct is_arithmetic<unsigned __int128> : ::std::true_type {};
template <>
struct is_integral<__int128> : ::std::true_type {};
template <>
struct is_integral<unsigned __int128> : ::std::true_type {};
template <>
struct make_unsigned<__int128> {
typedef unsigned __int128 type;
};
template <>
struct make_signed<__int128> {
typedef __int128 type;
};
template <>
struct make_unsigned<unsigned __int128> {
typedef unsigned __int128 type;
};
template <>
struct make_signed<unsigned __int128> {
typedef __int128 type;
};
template <>
struct is_signed<__int128> : ::std::true_type {};
template <>
struct is_unsigned<unsigned __int128> : ::std::true_type {};
FOLLY_NAMESPACE_STD_END
#endif // FOLLY_SUPPLY_MISSING_INT128_TRAITS
namespace folly {
/**
* Extension point for containers to provide an order such that if entries are
* inserted into a new instance in that order, iteration order of the new
* instance matches the original's. This can be useful for containers that have
* defined but non-FIFO iteration order, such as F14Vector*.
*
* Should return an iterable view (a type that provides begin() and end()).
*
* Containers should provide overloads in their own namespace; resolution is
* expected to be done via ADL.
*/
template <typename Container>
const Container& order_preserving_reinsertion_view(const Container& container) {
return container;
}
} // namespace folly