20 General utilities library [utilities]

20.12 Memory resources [mem.res]

20.12.2 Class memory_­resource [mem.res.class]

20.12.2.1 General [mem.res.class.general]

The memory_­resource class is an abstract interface to an unbounded set of classes encapsulating memory resources.
namespace std::pmr { class memory_resource { static constexpr size_t max_align = alignof(max_align_t); // exposition only public: memory_resource() = default; memory_resource(const memory_resource&) = default; virtual ~memory_resource(); memory_resource& operator=(const memory_resource&) = default; [[nodiscard]] void* allocate(size_t bytes, size_t alignment = max_align); void deallocate(void* p, size_t bytes, size_t alignment = max_align); bool is_equal(const memory_resource& other) const noexcept; private: virtual void* do_allocate(size_t bytes, size_t alignment) = 0; virtual void do_deallocate(void* p, size_t bytes, size_t alignment) = 0; virtual bool do_is_equal(const memory_resource& other) const noexcept = 0; }; }

20.12.2.2 Public member functions [mem.res.public]

~memory_resource();
Effects: Destroys this memory_­resource.
[[nodiscard]] void* allocate(size_t bytes, size_t alignment = max_align);
Effects: Equivalent to: return do_­allocate(bytes, alignment);
void deallocate(void* p, size_t bytes, size_t alignment = max_align);
Effects: Equivalent to do_­deallocate(p, bytes, alignment).
bool is_equal(const memory_resource& other) const noexcept;
Effects: Equivalent to: return do_­is_­equal(other);

20.12.2.3 Private virtual member functions [mem.res.private]

virtual void* do_allocate(size_t bytes, size_t alignment) = 0;
Preconditions: alignment is a power of two.
Returns: A derived class shall implement this function to return a pointer to allocated storage ([basic.stc.dynamic.allocation]) with a size of at least bytes, aligned to the specified alignment.
Throws: A derived class implementation shall throw an appropriate exception if it is unable to allocate memory with the requested size and alignment.
virtual void do_deallocate(void* p, size_t bytes, size_t alignment) = 0;
Preconditions: p was returned from a prior call to allocate(bytes, alignment) on a memory resource equal to *this, and the storage at p has not yet been deallocated.
Effects: A derived class shall implement this function to dispose of allocated storage.
Throws: Nothing.
virtual bool do_is_equal(const memory_resource& other) const noexcept = 0;
Returns: A derived class shall implement this function to return true if memory allocated from this can be deallocated from other and vice-versa, otherwise false.
[Note 1:
It is possible that the most-derived type of other does not match the type of this.
For a derived class D, an implementation of this function can immediately return false if dynamic_­cast<const D*>(&other) == nullptr.
— end note]

20.12.2.4 Equality [mem.res.eq]

bool operator==(const memory_resource& a, const memory_resource& b) noexcept;
Returns: &a == &b || a.is_­equal(b).