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Document number: N3974

Date: 2014-05-28

Polymorphic Deleter for Unique Pointers

by Marco Arena, Davide di Gennaro and Peter Sommerlad

Excerpt:

... However, with heap-allocated polymorphic types in C++11 code this means one needs to use shared_ptr<Base> and make_shared<Derived> to avoid the need to define a virtual destructor for Base. There is no standard deleter for unique_ptr that will allow to safely use unique_ptr<Base> if Base doesn't define a virtual destructor. Such a misuse is not even detectable easily. However, always using shared_ptr to get its desired deleter magic would also incur the overhead of the atomic reference counter and the overhead of full type erasure.

This proposal tries to ease the burden for programmers of heap allocated polymorphic classes and gives them the option to use unique_ptr with a standard provided deleter classes that either check correct provisioning of a virtual destructor in the base class or provide a slight overhead infrastructure for safe deletes through base type pointers, even if the base class doesn't define a virtual destructor.