// 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
//
// https://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/base/macros.h"
#include "absl/meta/type_traits.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
// -----------------------------------------------------------------------------
// Function Template: WrapUnique()
// -----------------------------------------------------------------------------
//
// Adopts ownership from a raw pointer and transfers it to the returned
// `std::unique_ptr`, whose type is deduced. Because of this deduction, *do not*
// specify the template type `T` when calling `WrapUnique`.
//
// Example:
// X* NewX(int, int);
// auto x = WrapUnique(NewX(1, 2)); // 'x' is std::unique_ptr<X>.
//
// Do not call WrapUnique with an explicit type, as in
// `WrapUnique<X>(NewX(1, 2))`. The purpose of WrapUnique is to automatically
// deduce the pointer type. If you wish to make the type explicit, just use
// `std::unique_ptr` directly.
//
// auto x = std::unique_ptr<X>(NewX(1, 2));
// - or -
// std::unique_ptr<X> x(NewX(1, 2));
//
// While `absl::WrapUnique` is useful for capturing the output of a raw
// pointer factory, 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
// gcc 4.8 has __cplusplus at 201301 but the libstdc++ shipped with it doesn't
// define make_unique. Other supported compilers either just define __cplusplus
// as 201103 but have make_unique (msvc), or have make_unique whenever
// __cplusplus > 201103 (clang).
#if (__cplusplus > 201103L || defined(_MSC_VER)) && \
!(defined(__GLIBCXX__) && !defined(__cpp_lib_make_unique))
using std::make_unique;
#else
// -----------------------------------------------------------------------------
// 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)[https://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;
#endif
// -----------------------------------------------------------------------------
// Function Template: RawPtr()
// -----------------------------------------------------------------------------
//
// Extracts the raw pointer from a pointer-like value `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(std::addressof(*ptr)) {
// ptr is a forwarding reference to support Ts with non-const operators.
return (ptr != nullptr) ? std::addressof(*ptr) : nullptr;
}
inline std::nullptr_t RawPtr(std::nullptr_t) { return nullptr; }
// -----------------------------------------------------------------------------
// Function Template: ShareUniquePtr()
// -----------------------------------------------------------------------------
//
// Adopts a `std::unique_ptr` rvalue and returns a `std::shared_ptr` of deduced
// type. Ownership (if any) of the held value is transferred to the returned
// 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, and more
// generally it works for *any* deleter of the `unique_ptr` (single-object
// deleter, array deleter, or any custom deleter), since the deleter is adopted
// by the shared pointer as well. The deleter is copied (unless it is a
// reference).
//
// 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>
constexpr bool HasRebindAlloc(...) {
return false;
}
template <typename T, typename U>
constexpr bool HasRebindAlloc(typename T::template rebind<U>::other*) {
return true;
}
template <typename T, typename U, bool = HasRebindAlloc<T, U>(nullptr)>
struct RebindAlloc {
using type = typename RebindFirstArg<T, U>::type;
};
template <typename T, typename U>
struct RebindAlloc<T, U, true> {
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 defined(ABSL_ALLOCATOR_NOTHROW) && 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 memory_internal {
template <typename Allocator, typename Iterator, typename... Args>
void ConstructRange(Allocator& alloc, Iterator first, Iterator last,
const Args&... args) {
for (Iterator cur = first; cur != last; ++cur) {
ABSL_INTERNAL_TRY {
std::allocator_traits<Allocator>::construct(alloc, std::addressof(*cur),
args...);
}
ABSL_INTERNAL_CATCH_ANY {
while (cur != first) {
--cur;
std::allocator_traits<Allocator>::destroy(alloc, std::addressof(*cur));
}
ABSL_INTERNAL_RETHROW;
}
}
}
template <typename Allocator, typename Iterator, typename InputIterator>
void CopyRange(Allocator& alloc, Iterator destination, InputIterator first,
InputIterator last) {
for (Iterator cur = destination; first != last;
static_cast<void>(++cur), static_cast<void>(++first)) {
ABSL_INTERNAL_TRY {
std::allocator_traits<Allocator>::construct(alloc, std::addressof(*cur),
*first);
}
ABSL_INTERNAL_CATCH_ANY {
while (cur != destination) {
--cur;
std::allocator_traits<Allocator>::destroy(alloc, std::addressof(*cur));
}
ABSL_INTERNAL_RETHROW;
}
}
}
} // namespace memory_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_MEMORY_MEMORY_H_
