Member functions for derived information in a class

Question

While designing an interface for a class I normally get caught in two minds whether should I provide member functions which can be calculated / derived by using combinations of

Answer 1

The answer is proabably "it depends"...

If the class is part of a public interface to a library that will be used by many different callers then there's a good argument for providing a multitude of functionality to make it easy to use, including some duplication and/or crossover. However, if the class is only being used by a single upstream caller then it probably doesn't make sense to provide multiple ways to achieve the same thing. Remember that all the code in the interface has to be tested and documented, so there is always a cost to adding that one last bit of functionality.