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+// Copyright 2017 The Abseil Authors.
+//
+// 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.
+//
+// -----------------------------------------------------------------------------
+// File: memory.h
+// -----------------------------------------------------------------------------
+//
+// This header file contains utility functions for managing the creation and
+// conversion of smart pointers. This file is an extension to the C++
+// standard <memory> library header file.
+
+#ifndef ABSL_MEMORY_MEMORY_H_
+#define ABSL_MEMORY_MEMORY_H_
+
+#include <cstddef>
+#include <limits>
+#include <memory>
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+
+// -----------------------------------------------------------------------------
+// Function Template: WrapUnique()
+// -----------------------------------------------------------------------------
+//
+// Transfers ownership of a raw pointer to a `std::unique_ptr`. The returned
+// value is a `std::unique_ptr` of deduced type.
+//
+// Example:
+// X* NewX(int, int);
+// auto x = WrapUnique(NewX(1, 2)); // 'x' is std::unique_ptr<X>.
+//
+// `absl::WrapUnique` is useful for capturing the output of a raw pointer
+// factory. However, prefer 'absl::make_unique<T>(args...) over
+// 'absl::WrapUnique(new T(args...))'.
+//
+// auto x = WrapUnique(new X(1, 2)); // works, but nonideal.
+// auto x = make_unique<X>(1, 2); // safer, standard, avoids raw 'new'.
+//
+// Note that `absl::WrapUnique(p)` is valid only if `delete p` is a valid
+// expression. In particular, `absl::WrapUnique()` cannot wrap pointers to
+// arrays, functions or void, and it must not be used to capture pointers
+// obtained from array-new expressions (even though that would compile!).
+template <typename T>
+std::unique_ptr<T> WrapUnique(T* ptr) {
+ static_assert(!std::is_array<T>::value, "array types are unsupported");
+ static_assert(std::is_object<T>::value, "non-object types are unsupported");
+ return std::unique_ptr<T>(ptr);
+}
+
+namespace memory_internal {
+
+// Traits to select proper overload and return type for `absl::make_unique<>`.
+template <typename T>
+struct MakeUniqueResult {
+ using scalar = std::unique_ptr<T>;
+};
+template <typename T>
+struct MakeUniqueResult<T[]> {
+ using array = std::unique_ptr<T[]>;
+};
+template <typename T, size_t N>
+struct MakeUniqueResult<T[N]> {
+ using invalid = void;
+};
+
+} // namespace memory_internal
+
+// -----------------------------------------------------------------------------
+// Function Template: make_unique<T>()
+// -----------------------------------------------------------------------------
+//
+// Creates a `std::unique_ptr<>`, while avoiding issues creating temporaries
+// during the construction process. `absl::make_unique<>` also avoids redundant
+// type declarations, by avoiding the need to explicitly use the `new` operator.
+//
+// This implementation of `absl::make_unique<>` is designed for C++11 code and
+// will be replaced in C++14 by the equivalent `std::make_unique<>` abstraction.
+// `absl::make_unique<>` is designed to be 100% compatible with
+// `std::make_unique<>` so that the eventual migration will involve a simple
+// rename operation.
+//
+// For more background on why `std::unique_ptr<T>(new T(a,b))` is problematic,
+// see Herb Sutter's explanation on
+// (Exception-Safe Function Calls)[http://herbsutter.com/gotw/_102/].
+// (In general, reviewers should treat `new T(a,b)` with scrutiny.)
+//
+// Example usage:
+//
+// auto p = make_unique<X>(args...); // 'p' is a std::unique_ptr<X>
+// auto pa = make_unique<X[]>(5); // 'pa' is a std::unique_ptr<X[]>
+//
+// Three overloads of `absl::make_unique` are required:
+//
+// - For non-array T:
+//
+// Allocates a T with `new T(std::forward<Args> args...)`,
+// forwarding all `args` to T's constructor.
+// Returns a `std::unique_ptr<T>` owning that object.
+//
+// - For an array of unknown bounds T[]:
+//
+// `absl::make_unique<>` will allocate an array T of type U[] with
+// `new U[n]()` and return a `std::unique_ptr<U[]>` owning that array.
+//
+// Note that 'U[n]()' is different from 'U[n]', and elements will be
+// value-initialized. Note as well that `std::unique_ptr` will perform its
+// own destruction of the array elements upon leaving scope, even though
+// the array [] does not have a default destructor.
+//
+// NOTE: an array of unknown bounds T[] may still be (and often will be)
+// initialized to have a size, and will still use this overload. E.g:
+//
+// auto my_array = absl::make_unique<int[]>(10);
+//
+// - For an array of known bounds T[N]:
+//
+// `absl::make_unique<>` is deleted (like with `std::make_unique<>`) as
+// this overload is not useful.
+//
+// NOTE: an array of known bounds T[N] is not considered a useful
+// construction, and may cause undefined behavior in templates. E.g:
+//
+// auto my_array = absl::make_unique<int[10]>();
+//
+// In those cases, of course, you can still use the overload above and
+// simply initialize it to its desired size:
+//
+// auto my_array = absl::make_unique<int[]>(10);
+
+// `absl::make_unique` overload for non-array types.
+template <typename T, typename... Args>
+typename memory_internal::MakeUniqueResult<T>::scalar make_unique(
+ Args&&... args) {
+ return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
+}
+
+// `absl::make_unique` overload for an array T[] of unknown bounds.
+// The array allocation needs to use the `new T[size]` form and cannot take
+// element constructor arguments. The `std::unique_ptr` will manage destructing
+// these array elements.
+template <typename T>
+typename memory_internal::MakeUniqueResult<T>::array make_unique(size_t n) {
+ return std::unique_ptr<T>(new typename absl::remove_extent_t<T>[n]());
+}
+
+// `absl::make_unique` overload for an array T[N] of known bounds.
+// This construction will be rejected.
+template <typename T, typename... Args>
+typename memory_internal::MakeUniqueResult<T>::invalid make_unique(
+ Args&&... /* args */) = delete;
+
+// -----------------------------------------------------------------------------
+// Function Template: RawPtr()
+// -----------------------------------------------------------------------------
+//
+// Extracts the raw pointer from a pointer-like 'ptr'. `absl::RawPtr` is useful
+// within templates that need to handle a complement of raw pointers,
+// `std::nullptr_t`, and smart pointers.
+template <typename T>
+auto RawPtr(T&& ptr) -> decltype(&*ptr) {
+ // ptr is a forwarding reference to support Ts with non-const operators.
+ return (ptr != nullptr) ? &*ptr : nullptr;
+}
+inline std::nullptr_t RawPtr(std::nullptr_t) { return nullptr; }
+
+// -----------------------------------------------------------------------------
+// Function Template: ShareUniquePtr()
+// -----------------------------------------------------------------------------
+//
+// Transforms a `std::unique_ptr` rvalue into a `std::shared_ptr`. The returned
+// value is a `std::shared_ptr` of deduced type and ownership is transferred to
+// the shared pointer.
+//
+// Example:
+//
+// auto up = absl::make_unique<int>(10);
+// auto sp = absl::ShareUniquePtr(std::move(up)); // shared_ptr<int>
+// CHECK_EQ(*sp, 10);
+// CHECK(up == nullptr);
+//
+// Note that this conversion is correct even when T is an array type, although
+// the resulting shared pointer may not be very useful.
+//
+// Implements the resolution of [LWG 2415](http://wg21.link/lwg2415), by which a
+// null shared pointer does not attempt to call the deleter.
+template <typename T, typename D>
+std::shared_ptr<T> ShareUniquePtr(std::unique_ptr<T, D>&& ptr) {
+ return ptr ? std::shared_ptr<T>(std::move(ptr)) : std::shared_ptr<T>();
+}
+
+// -----------------------------------------------------------------------------
+// Function Template: WeakenPtr()
+// -----------------------------------------------------------------------------
+//
+// Creates a weak pointer associated with a given shared pointer. The returned
+// value is a `std::weak_ptr` of deduced type.
+//
+// Example:
+//
+// auto sp = std::make_shared<int>(10);
+// auto wp = absl::WeakenPtr(sp);
+// CHECK_EQ(sp.get(), wp.lock().get());
+// sp.reset();
+// CHECK(wp.lock() == nullptr);
+//
+template <typename T>
+std::weak_ptr<T> WeakenPtr(const std::shared_ptr<T>& ptr) {
+ return std::weak_ptr<T>(ptr);
+}
+
+namespace memory_internal {
+
+// ExtractOr<E, O, D>::type evaluates to E<O> if possible. Otherwise, D.
+template <template <typename> class Extract, typename Obj, typename Default,
+ typename>
+struct ExtractOr {
+ using type = Default;
+};
+
+template <template <typename> class Extract, typename Obj, typename Default>
+struct ExtractOr<Extract, Obj, Default, void_t<Extract<Obj>>> {
+ using type = Extract<Obj>;
+};
+
+template <template <typename> class Extract, typename Obj, typename Default>
+using ExtractOrT = typename ExtractOr<Extract, Obj, Default, void>::type;
+
+// Extractors for the features of allocators.
+template <typename T>
+using GetPointer = typename T::pointer;
+
+template <typename T>
+using GetConstPointer = typename T::const_pointer;
+
+template <typename T>
+using GetVoidPointer = typename T::void_pointer;
+
+template <typename T>
+using GetConstVoidPointer = typename T::const_void_pointer;
+
+template <typename T>
+using GetDifferenceType = typename T::difference_type;
+
+template <typename T>
+using GetSizeType = typename T::size_type;
+
+template <typename T>
+using GetPropagateOnContainerCopyAssignment =
+ typename T::propagate_on_container_copy_assignment;
+
+template <typename T>
+using GetPropagateOnContainerMoveAssignment =
+ typename T::propagate_on_container_move_assignment;
+
+template <typename T>
+using GetPropagateOnContainerSwap = typename T::propagate_on_container_swap;
+
+template <typename T>
+using GetIsAlwaysEqual = typename T::is_always_equal;
+
+template <typename T>
+struct GetFirstArg;
+
+template <template <typename...> class Class, typename T, typename... Args>
+struct GetFirstArg<Class<T, Args...>> {
+ using type = T;
+};
+
+template <typename Ptr, typename = void>
+struct ElementType {
+ using type = typename GetFirstArg<Ptr>::type;
+};
+
+template <typename T>
+struct ElementType<T, void_t<typename T::element_type>> {
+ using type = typename T::element_type;
+};
+
+template <typename T, typename U>
+struct RebindFirstArg;
+
+template <template <typename...> class Class, typename T, typename... Args,
+ typename U>
+struct RebindFirstArg<Class<T, Args...>, U> {
+ using type = Class<U, Args...>;
+};
+
+template <typename T, typename U, typename = void>
+struct RebindPtr {
+ using type = typename RebindFirstArg<T, U>::type;
+};
+
+template <typename T, typename U>
+struct RebindPtr<T, U, void_t<typename T::template rebind<U>>> {
+ using type = typename T::template rebind<U>;
+};
+
+template <typename T, typename U, typename = void>
+struct RebindAlloc {
+ using type = typename RebindFirstArg<T, U>::type;
+};
+
+template <typename T, typename U>
+struct RebindAlloc<T, U, void_t<typename T::template rebind<U>::other>> {
+ using type = typename T::template rebind<U>::other;
+};
+
+} // namespace memory_internal
+
+// -----------------------------------------------------------------------------
+// Class Template: pointer_traits
+// -----------------------------------------------------------------------------
+//
+// An implementation of C++11's std::pointer_traits.
+//
+// Provided for portability on toolchains that have a working C++11 compiler,
+// but the standard library is lacking in C++11 support. For example, some
+// version of the Android NDK.
+//
+
+template <typename Ptr>
+struct pointer_traits {
+ using pointer = Ptr;
+
+ // element_type:
+ // Ptr::element_type if present. Otherwise T if Ptr is a template
+ // instantiation Template<T, Args...>
+ using element_type = typename memory_internal::ElementType<Ptr>::type;
+
+ // difference_type:
+ // Ptr::difference_type if present, otherwise std::ptrdiff_t
+ using difference_type =
+ memory_internal::ExtractOrT<memory_internal::GetDifferenceType, Ptr,
+ std::ptrdiff_t>;
+
+ // rebind:
+ // Ptr::rebind<U> if exists, otherwise Template<U, Args...> if Ptr is a
+ // template instantiation Template<T, Args...>
+ template <typename U>
+ using rebind = typename memory_internal::RebindPtr<Ptr, U>::type;
+
+ // pointer_to:
+ // Calls Ptr::pointer_to(r)
+ static pointer pointer_to(element_type& r) { // NOLINT(runtime/references)
+ return Ptr::pointer_to(r);
+ }
+};
+
+// Specialization for T*.
+template <typename T>
+struct pointer_traits<T*> {
+ using pointer = T*;
+ using element_type = T;
+ using difference_type = std::ptrdiff_t;
+
+ template <typename U>
+ using rebind = U*;
+
+ // pointer_to:
+ // Calls std::addressof(r)
+ static pointer pointer_to(
+ element_type& r) noexcept { // NOLINT(runtime/references)
+ return std::addressof(r);
+ }
+};
+
+// -----------------------------------------------------------------------------
+// Class Template: allocator_traits
+// -----------------------------------------------------------------------------
+//
+// A C++11 compatible implementation of C++17's std::allocator_traits.
+//
+template <typename Alloc>
+struct allocator_traits {
+ using allocator_type = Alloc;
+
+ // value_type:
+ // Alloc::value_type
+ using value_type = typename Alloc::value_type;
+
+ // pointer:
+ // Alloc::pointer if present, otherwise value_type*
+ using pointer = memory_internal::ExtractOrT<memory_internal::GetPointer,
+ Alloc, value_type*>;
+
+ // const_pointer:
+ // Alloc::const_pointer if present, otherwise
+ // absl::pointer_traits<pointer>::rebind<const value_type>
+ using const_pointer =
+ memory_internal::ExtractOrT<memory_internal::GetConstPointer, Alloc,
+ typename absl::pointer_traits<pointer>::
+ template rebind<const value_type>>;
+
+ // void_pointer:
+ // Alloc::void_pointer if present, otherwise
+ // absl::pointer_traits<pointer>::rebind<void>
+ using void_pointer = memory_internal::ExtractOrT<
+ memory_internal::GetVoidPointer, Alloc,
+ typename absl::pointer_traits<pointer>::template rebind<void>>;
+
+ // const_void_pointer:
+ // Alloc::const_void_pointer if present, otherwise
+ // absl::pointer_traits<pointer>::rebind<const void>
+ using const_void_pointer = memory_internal::ExtractOrT<
+ memory_internal::GetConstVoidPointer, Alloc,
+ typename absl::pointer_traits<pointer>::template rebind<const void>>;
+
+ // difference_type:
+ // Alloc::difference_type if present, otherwise
+ // absl::pointer_traits<pointer>::difference_type
+ using difference_type = memory_internal::ExtractOrT<
+ memory_internal::GetDifferenceType, Alloc,
+ typename absl::pointer_traits<pointer>::difference_type>;
+
+ // size_type:
+ // Alloc::size_type if present, otherwise
+ // std::make_unsigned<difference_type>::type
+ using size_type = memory_internal::ExtractOrT<
+ memory_internal::GetSizeType, Alloc,
+ typename std::make_unsigned<difference_type>::type>;
+
+ // propagate_on_container_copy_assignment:
+ // Alloc::propagate_on_container_copy_assignment if present, otherwise
+ // std::false_type
+ using propagate_on_container_copy_assignment = memory_internal::ExtractOrT<
+ memory_internal::GetPropagateOnContainerCopyAssignment, Alloc,
+ std::false_type>;
+
+ // propagate_on_container_move_assignment:
+ // Alloc::propagate_on_container_move_assignment if present, otherwise
+ // std::false_type
+ using propagate_on_container_move_assignment = memory_internal::ExtractOrT<
+ memory_internal::GetPropagateOnContainerMoveAssignment, Alloc,
+ std::false_type>;
+
+ // propagate_on_container_swap:
+ // Alloc::propagate_on_container_swap if present, otherwise std::false_type
+ using propagate_on_container_swap =
+ memory_internal::ExtractOrT<memory_internal::GetPropagateOnContainerSwap,
+ Alloc, std::false_type>;
+
+ // is_always_equal:
+ // Alloc::is_always_equal if present, otherwise std::is_empty<Alloc>::type
+ using is_always_equal =
+ memory_internal::ExtractOrT<memory_internal::GetIsAlwaysEqual, Alloc,
+ typename std::is_empty<Alloc>::type>;
+
+ // rebind_alloc:
+ // Alloc::rebind<T>::other if present, otherwise Alloc<T, Args> if this Alloc
+ // is Alloc<U, Args>
+ template <typename T>
+ using rebind_alloc = typename memory_internal::RebindAlloc<Alloc, T>::type;
+
+ // rebind_traits:
+ // absl::allocator_traits<rebind_alloc<T>>
+ template <typename T>
+ using rebind_traits = absl::allocator_traits<rebind_alloc<T>>;
+
+ // allocate(Alloc& a, size_type n):
+ // Calls a.allocate(n)
+ static pointer allocate(Alloc& a, // NOLINT(runtime/references)
+ size_type n) {
+ return a.allocate(n);
+ }
+
+ // allocate(Alloc& a, size_type n, const_void_pointer hint):
+ // Calls a.allocate(n, hint) if possible.
+ // If not possible, calls a.allocate(n)
+ static pointer allocate(Alloc& a, size_type n, // NOLINT(runtime/references)
+ const_void_pointer hint) {
+ return allocate_impl(0, a, n, hint);
+ }
+
+ // deallocate(Alloc& a, pointer p, size_type n):
+ // Calls a.deallocate(p, n)
+ static void deallocate(Alloc& a, pointer p, // NOLINT(runtime/references)
+ size_type n) {
+ a.deallocate(p, n);
+ }
+
+ // construct(Alloc& a, T* p, Args&&... args):
+ // Calls a.construct(p, std::forward<Args>(args)...) if possible.
+ // If not possible, calls
+ // ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...)
+ template <typename T, typename... Args>
+ static void construct(Alloc& a, T* p, // NOLINT(runtime/references)
+ Args&&... args) {
+ construct_impl(0, a, p, std::forward<Args>(args)...);
+ }
+
+ // destroy(Alloc& a, T* p):
+ // Calls a.destroy(p) if possible. If not possible, calls p->~T().
+ template <typename T>
+ static void destroy(Alloc& a, T* p) { // NOLINT(runtime/references)
+ destroy_impl(0, a, p);
+ }
+
+ // max_size(const Alloc& a):
+ // Returns a.max_size() if possible. If not possible, returns
+ // std::numeric_limits<size_type>::max() / sizeof(value_type)
+ static size_type max_size(const Alloc& a) { return max_size_impl(0, a); }
+
+ // select_on_container_copy_construction(const Alloc& a):
+ // Returns a.select_on_container_copy_construction() if possible.
+ // If not possible, returns a.
+ static Alloc select_on_container_copy_construction(const Alloc& a) {
+ return select_on_container_copy_construction_impl(0, a);
+ }
+
+ private:
+ template <typename A>
+ static auto allocate_impl(int, A& a, // NOLINT(runtime/references)
+ size_type n, const_void_pointer hint)
+ -> decltype(a.allocate(n, hint)) {
+ return a.allocate(n, hint);
+ }
+ static pointer allocate_impl(char, Alloc& a, // NOLINT(runtime/references)
+ size_type n, const_void_pointer) {
+ return a.allocate(n);
+ }
+
+ template <typename A, typename... Args>
+ static auto construct_impl(int, A& a, // NOLINT(runtime/references)
+ Args&&... args)
+ -> decltype(a.construct(std::forward<Args>(args)...)) {
+ a.construct(std::forward<Args>(args)...);
+ }
+
+ template <typename T, typename... Args>
+ static void construct_impl(char, Alloc&, T* p, Args&&... args) {
+ ::new (static_cast<void*>(p)) T(std::forward<Args>(args)...);
+ }
+
+ template <typename A, typename T>
+ static auto destroy_impl(int, A& a, // NOLINT(runtime/references)
+ T* p) -> decltype(a.destroy(p)) {
+ a.destroy(p);
+ }
+ template <typename T>
+ static void destroy_impl(char, Alloc&, T* p) {
+ p->~T();
+ }
+
+ template <typename A>
+ static auto max_size_impl(int, const A& a) -> decltype(a.max_size()) {
+ return a.max_size();
+ }
+ static size_type max_size_impl(char, const Alloc&) {
+ return std::numeric_limits<size_type>::max() / sizeof(value_type);
+ }
+
+ template <typename A>
+ static auto select_on_container_copy_construction_impl(int, const A& a)
+ -> decltype(a.select_on_container_copy_construction()) {
+ return a.select_on_container_copy_construction();
+ }
+ static Alloc select_on_container_copy_construction_impl(char,
+ const Alloc& a) {
+ return a;
+ }
+};
+
+namespace memory_internal {
+
+// This template alias transforms Alloc::is_nothrow into a metafunction with
+// Alloc as a parameter so it can be used with ExtractOrT<>.
+template <typename Alloc>
+using GetIsNothrow = typename Alloc::is_nothrow;
+
+} // namespace memory_internal
+
+// ABSL_ALLOCATOR_NOTHROW is a build time configuration macro for user to
+// specify whether the default allocation function can throw or never throws.
+// If the allocation function never throws, user should define it to a non-zero
+// value (e.g. via `-DABSL_ALLOCATOR_NOTHROW`).
+// If the allocation function can throw, user should leave it undefined or
+// define it to zero.
+//
+// allocator_is_nothrow<Alloc> is a traits class that derives from
+// Alloc::is_nothrow if present, otherwise std::false_type. It's specialized
+// for Alloc = std::allocator<T> for any type T according to the state of
+// ABSL_ALLOCATOR_NOTHROW.
+//
+// default_allocator_is_nothrow is a class that derives from std::true_type
+// when the default allocator (global operator new) never throws, and
+// std::false_type when it can throw. It is a convenience shorthand for writing
+// allocator_is_nothrow<std::allocator<T>> (T can be any type).
+// NOTE: allocator_is_nothrow<std::allocator<T>> is guaranteed to derive from
+// the same type for all T, because users should specialize neither
+// allocator_is_nothrow nor std::allocator.
+template <typename Alloc>
+struct allocator_is_nothrow
+ : memory_internal::ExtractOrT<memory_internal::GetIsNothrow, Alloc,
+ std::false_type> {};
+
+#if ABSL_ALLOCATOR_NOTHROW
+template <typename T>
+struct allocator_is_nothrow<std::allocator<T>> : std::true_type {};
+struct default_allocator_is_nothrow : std::true_type {};
+#else
+struct default_allocator_is_nothrow : std::false_type {};
+#endif
+
+} // namespace absl
+
+#endif // ABSL_MEMORY_MEMORY_H_