20 Memory management library [mem]

20.4 Memory resources [mem.res]

20.4.3 Class template polymorphic_allocator [mem.poly.allocator.class]

20.4.3.3 Member functions [mem.poly.allocator.mem]

[[nodiscard]] Tp* allocate(size_t n);

Effects: If numeric_limits<size_t>::max() / sizeof(Tp) < n, throws bad_array_new_length.

Otherwise equivalent to: return static_cast<Tp*>(memory_rsrc->allocate(n * sizeof(Tp), alignof(Tp)));

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void deallocate(Tp* p, size_t n);

Preconditions: p was allocated from a memory resource x, equal to *memory_rsrc, using x.allocate(n * sizeof(Tp), alignof(Tp)).

Effects: Equivalent to memory_rsrc->deallocate(p, n * sizeof(Tp), alignof(Tp)).

Throws: Nothing.

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[[nodiscard]] void* allocate_bytes(size_t nbytes, size_t alignment = alignof(max_align_t));

Effects: Equivalent to: return memory_rsrc->allocate(nbytes, alignment);

[Note 1:

The return type is void* (rather than, e.g., byte*) to support conversion to an arbitrary pointer type U* by static_cast<U*>, thus facilitating construction of a U object in the allocated memory.

— end note]

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void deallocate_bytes(void* p, size_t nbytes, size_t alignment = alignof(max_align_t));

Effects: Equivalent to memory_rsrc->deallocate(p, nbytes, alignment).

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template<class T>
  [[nodiscard]] T* allocate_object(size_t n = 1);

Effects: Allocates memory suitable for holding an array of n objects of type T, as follows:

(8.1)
if numeric_limits<size_t>::max() / sizeof(T) < n, throws bad_array_new_length,
(8.2)
otherwise equivalent to: return static_cast<T*>(allocate_bytes(n*sizeof(T), alignof(T)));

[Note 2:

T is not deduced and must therefore be provided as a template argument.

— end note]

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template<class T>
  void deallocate_object(T* p, size_t n = 1);

Effects: Equivalent to deallocate_bytes(p, n*sizeof(T), alignof(T)).

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template<class T, class... CtorArgs>
  [[nodiscard]] T* new_object(CtorArgs&&... ctor_args);

Effects: Allocates and constructs an object of type T, as follows.

Equivalent to: T* p = allocate_object<T>(); try { construct(p, std::forward<CtorArgs>(ctor_args)...); } catch (...) { deallocate_object(p); throw; } return p;

[Note 3:

T is not deduced and must therefore be provided as a template argument.

— end note]

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template<class T>
  void delete_object(T* p);

Effects: Equivalent to: allocator_traits<polymorphic_allocator>::destroy(*this, p); deallocate_object(p);

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template<class T, class... Args>
  void construct(T* p, Args&&... args);

Mandates: Uses-allocator construction of T with allocator *this (see [allocator.uses.construction]) and constructor arguments std::forward<Args>(args)... is well-formed.

Effects: Construct a T object in the storage whose address is represented by p by uses-allocator construction with allocator *this and constructor arguments std::forward<Args>(args)....

Throws: Nothing unless the constructor for T throws.

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polymorphic_allocator select_on_container_copy_construction() const;

Returns: polymorphic_allocator().

[Note 4:

The memory resource is not propagated.

— end note]

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memory_resource* resource() const;

Returns: memory_rsrc.