Delete virtual function from a derived class

Question

I have a virtual base class function which should never be used in a particular derived class. Is there a way to \'delete\' it? I can of course just give it an empty definitio

Answer 1

What you can do is simply throwing an exception in the derived implementation. For example, the Java Collections framework does this quite excessively: When an update operation is performed on a collection that is immutable, the corresponding method simply throws an UnsupportedOperationException. You can do the same in C++.

Of course, this will show a malicious use of the function only at runtime; not at compile time. However, with virtual methods, you are unable to catch such errors at compile time anyway because of polymorphism. E.g.:

B* b = new D();
b.f();

Here, you store a D in a B* variable. So, even if there was a way to tell the compiler that you are not allowed to call f on a D, the compiler would be unable to report this error here, because it only sees B.