cppdraft_translate/cppdraft/mem/poly/allocator/class/general.md

[mem.poly.allocator.class.general]

20 Memory management library [mem]

20.5 Memory resources [mem.res]

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

20.5.3.1 General [mem.poly.allocator.class.general]

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A specialization of class template pmr​::​polymorphic_allocator meets the Cpp17Allocator requirements ([allocator.requirements.general]) if its template argument is a cv-unqualified object type.

Constructed with different memory resources, different instances of the same specialization of pmr​::​polymorphic_allocator can exhibit entirely different allocation behavior.

This runtime polymorphism allows objects that use polymorphic_allocator to behave as if they used different allocator types at run time even though they use the same static allocator type.

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A specialization of class template pmr​::​polymorphic_allocator meets the allocator completeness requirements ([allocator.requirements.completeness]) if its template argument is a cv-unqualified object type.

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namespace std::pmr {template class polymorphic_allocator { memory_resource* memory_rsrc; // exposition onlypublic:using value_type = Tp; // [mem.poly.allocator.ctor], constructors polymorphic_allocator() noexcept; polymorphic_allocator(memory_resource* r);

polymorphic_allocator(const polymorphic_allocator& other) = default; template polymorphic_allocator(const polymorphic_allocator& other) noexcept;

polymorphic_allocator& operator=(const polymorphic_allocator&) = delete; // [mem.poly.allocator.mem], member functions Tp* allocate(size_t n); void deallocate(Tp* p, size_t n); void* allocate_bytes(size_t nbytes, size_t alignment = alignof(max_align_t)); void deallocate_bytes(void* p, size_t nbytes, size_t alignment = alignof(max_align_t)); template T* allocate_object(size_t n = 1); template void deallocate_object(T* p, size_t n = 1); template<class T, class... CtorArgs> T* new_object(CtorArgs&&... ctor_args); template void delete_object(T* p); template<class T, class... Args>void construct(T* p, Args&&... args); templatevoid destroy(T* p);

polymorphic_allocator select_on_container_copy_construction() const;

memory_resource* resource() const; // friendsfriend bool operator==(const polymorphic_allocator& a, const polymorphic_allocator& b) noexcept {return *a.resource() == *b.resource(); }};}