class Base
{
protected:
   virtual ~Base() {}
   virtual void MethodThatDoesAThing() = 0;
};

class Derived : public Base
{
public:
   virtual void MethodThatDoesAThing() override;
};

void Callee(Base* base)
{
   base->MethodThatDoesAThing();
}

void Caller()
{
    static Derived derived;
    Callee(&derived);
}

C++ allows overriding your parent's privates.

[edit] Wait... How does Callee not generate an error when it calls a protected function??

[edit2] how are you passing a Derived& to a function that takes a Base*? :P

I've run into similar problems with some programming projects for school.

i had one project where I had to build a basic ATM and couldn't figure out why the balance for the second person was showing the first person's balance and why the withdraw amount was adding to the balance. I swear it took me longer than it should have to realize that when I duplicated the code for my deposit function and for the second customer I forgot to go in and change the computation signs even though I changed the variable from deposit to withdraw and forgot to change my customer variable form customer1 to customer2. I felt so dumb when I realized it.