I have read a few times that people sometimes wish that std::vector (or other containers) had a virtual destructor. [snip] This allows one to write something like:
struct person { string first_name; string last_name; }; class people : public virtual_vector<person> { public: //extra methods };
Is this useful?
unless I mis-read (or mis-understood...far more likely) a lot of books on how C++ works, I don't believe there is any reason for what _you've_ shown to need a virtual destructor.
You have mis-read or mis-understood (or you need better books). Consider: virtual_vector<person>* p = new people;
I guees I wasn't clear.. I was suggesting that virtual_vector has no need for existence.
delete p; That invokes undefined behaviour unless virtual_vector<person> has a virtual destructor.
are you suggesting that if it were class people: public std::vector<person> {.....}; as above the same would be true? not "in practice", "in theory".
Absolutely. See 5.3.5/1 of the standard where this is explicitly called out as undefined behaviour.
Yes, it you are trying to delete pointers to 'people' through base class you do need virtual destructor. But: 1. In general in bad idea to inherit from STL container. Most probably you need a different relatationship (hint: containment) 2. If you insist on inheritance you still in most cases wouldn't need virtual destructor: don't delete through pointers on vector. To reinforce this you could employ either private inheritance or protected destructor in wrapper around vector. In any case this is not a type of idiom anyone need to promote. Gennadiy