20 General utilities library [utilities]

20.12 Memory resources [mem.res]

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

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

[[nodiscard]] Tp* allocate(size_t n);
Effects: If SIZE_­MAX / sizeof(Tp) < n, throws length_­error.
Otherwise equivalent to:
return static_cast<Tp*>(memory_rsrc->allocate(n * sizeof(Tp), alignof(Tp)));
void deallocate(Tp* p, size_t n);
Requires: 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.
void* allocate_bytes(size_t nbytes, size_t alignment = alignof(max_align_t));
Effects: Equivalent to: return memory_­rsrc->allocate(nbytes, alignment);
[Note
:
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.
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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).
template<class T> T* allocate_object(size_t n = 1);
Effects: Allocates memory suitable for holding an array of n objects of type T, as follows:
  • if SIZE_­MAX / sizeof(T) < n, throws length_­error,
  • otherwise equivalent to:
    return static_cast<T*>(allocate_bytes(n*sizeof(T), alignof(T)));
    
[Note
:
T is not deduced and must therefore be provided as a template argument.
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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)).
template<class T, class CtorArgs...> 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
:
T is not deduced and must therefore be provided as a template argument.
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]
template<class T> void delete_object(T* p);
Effects: Equivalent to:
destroy(p);
deallocate_object(p);
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.
template<class T> void destroy(T* p);
Effects: As if by p->~T().
polymorphic_allocator select_on_container_copy_construction() const;
Returns: polymorphic_­allocator().
[Note
:
The memory resource is not propagated.
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memory_resource* resource() const;
Returns: memory_­rsrc.