Question

Which inheritance makes more sense :

class SequentialIterator{ 
  SequentialIterator next(); 
};
class RandomAccessIterator : public SequentialIterator{
  RandomAccessIterator shift( int del );
};

or

class RandomAccessIterator {
  RandomAccessIterator shift( int del );
};
class SequentialIterator : public RandomAccessIterator{ 
  SequentialIterator next(); 
};

If I say “the derived class gives more complicated functionality than the base class” (first of all does this statement even make sense here), which is the more basic operation : next or shift?

EDIT : I’m actually designing interfaces for number sequences.

Answer 1

I think you’re looking at this from the wrong direction. In your first code-snippet, you essentially have three methods:

SequentialIterator.next()
RandomAccessIterator.next() // same as SequentialIterator.next()
RandomAccessIterator.shift(int)

In your second, you also have three methods, but they’re not the same ones:

RandomAccessIterator.shift(int)
SequentialIterator.shift(int) // same as RandomAccessIterator.shift(int)
SequentialIterator.next()

Looked at in this way, I think it should be clear that only the first version makes sense: a RandomAccessIterator class can reasonably offer a next() method, but a SequentialIterator class cannot reasonably offer a shift(int) method.

(This is assuming, of course, that there’s some reason to have one of them inherit from the other to begin with.)