polymorphic_allocator() noexcept;
polymorphic_allocator( const polymorphic_allocator& other ) noexcept = default;
template< class U >
polymorphic_allocator( const polymorphic_allocator<U>& other ) noexcept;
polymorphic_allocator( memory_resource* r);

Constructs a new polymorphic_allocator.

1) Constructs a polymorphic_allocator using the return value of std::experimental::pmr::get_default_resource() as the underlying memory resource.
2-3) Constructs a polymorphic_allocator using other.resource() as the underlying memory resource.
4) Constructs a polymorphic_allocator using r as the underlying memory resource. This constructor provides an implicit conversion from memory_resource*.


other - another polymorphic_allocator to copy from
r - pointer to the memory resource to use. May not be null.


4) Throws nothing.