std::pmr::polymorphic_allocator<T>:: select_on_container_copy_construction
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                    < cpp | memory | polymorphic allocator
                    
                                                            
                    |   polymorphic_allocator select_on_container_copy_construction() const;  | 
(since C++17) | |
Returns a default-constructed polymorphic_allocator object. 
Parameters
(none)
Return value
A default-constructed polymorphic_allocator object.
Notes
polymorphic_allocators do not propagate on container copy construction.
See also
|    obtains the allocator to use after copying a standard container  (public static member function of std::allocator_traits<Alloc>)  |