Extending enum in derived classes

Question

I have a class hierarchy, and each class in it has an exception class, derived in a parallel hierarchy, thus...

class Base
{
};

class Derived : public Base
{
};         


        

Answer 1

I would like, in the DerivedException class, to extend the enumeration type to include a new value THE_OTHER_REASON, so that the DerivedException class could hold any of the three values.

Just assign the first value of a new enum. This works since you're just using the enum as a way of declaring constants.

class DerivedException : public BaseException
{
    enum {THE_OTHER_REASON = THAT_REASON + 1, THE_REALLY_OTHER_REASON, ETC};
};

The problem is that you can't really expect uniqueness of the enums between derived classes, without defining a "chain" of derived classes (i.e. one starts its enums after another's). However, if you only need uniqueness within a single branch of the exception class tree, it can work fine.