JOAQUIN LOPEZ MU?Z wrote:
I find inheriting without virtual functions quite useful. The main reason for the virtual destructor rule goes back to Scott Meyers Effective C++. He points out that if you have Base <-- Derived and you call delete Base* the destructor of Derived is not called. In general, it's hard to ensure your derived classes won't need the destructor called and hence the rule. However, if Derived happens to have a trivial/empty destructor then, really there's no reason to call it.
I agree and disagree with your previous exposition :)
That's usual ;-)
I think deriving without virtual constructors is fine in those contexts when the user is not expected to delete passed objects, which are by far the most usual. Almost every function of the form
void foo([const] T& t)
won't certainly try to delete t, so it's fine to pass an use here an object of some class derived from T (like in your super_string case.)
Sure, but in the general case you could easily create an interface like this: void foo(T* t) hence Scott's design rule.
...snip...
What I don't agree with you in is your claim that "if Derived happens to have a trivial/empty destructor then, really there's no reason to call it." If my memory serves me well, deleting a Derived object through its Base non-virtual dtor is illegal according to the standard, regardless of whether D's dtor is trivial or not. You're merely being lucky with the actual behavior exhibited by compilers.
By the standard I believe it is technically undefined behavior. But as a practical matter it's defined exactly the same on all compilers -- call the base class destructor. Jeff