Template pattern

When you want to vary part of an algorithm then the template pattern might be for you.

You inherit from a base class which provides default behaviour or simply delegate all methods to the child object (i.e. effectively you're creating an virtual interface (if Ruby had them). Simply provide stub methods with raise UnimplmentedMethod or equivalent.

The template method (i.e. the shared method which calls out to subclassed methods) provides the overall procecessing.

disadvantage it's inheritence based.