One goal for the SOLID design principles is to limit the effects of change or extension on a design. Making a change to established software is a bit like casting a pebble into the sea: there will be an initial splash, followed by ripples of change spreading outward. When trying to fix or extend badly designed software, the initial splash radius covers everything; the ripples are large and lead to numerous problems. In well-designed software, the splash radius is tiny.
As a concrete example, consider a class to represent dominoes. Each tile has 2 numbers, from 0 to 6, leading to 28 distinct tiles. The class design looks more or less like a two-tuple. The overall collection of 28 tiles can be generated with a nested pair of for statements, or a generator expression with two for clauses.
In some games, however, the tiles could have an upper limit of 9...
