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It is actually super easy, barely an inconvenience, as long as you know the actual dynamic type at construction time.

For example shared-ptr to base can correctly invoke the correct derived type destructor even if the destructor is not virtual.

Edit: accidentally a word.

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You always know the actual dynamic type at construction time, how would you otherwise construct it?

> For example shared-ptr to base can correctly invoke the correct derived type

Invoke what exactly? Im sorry I don't understand what you're trying to say here.

I guess you can force all derivied types to implement a clone() function, such that box<T> can do the deep copy, but Id consider that a fairly big inconvenience for such a simple pointer type.

No need for T to have a clone function. You can use standard type erasure techniques. Consider how std:: function or std::any is implemented.

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