Constructing Independent Objects

The theme running through this is that sufficiency is sufficient. When an object has been identified as part of the solution to a problem and contributes to that solution to the extent needed (even if for now that extent is “demonstrate that a solution is viable”), then it is ready to use. There is no need to situate the object in a taxonomy of inherited classes, but if that helps to solve the problem, then by all means do it. There is no need to show that various objects demonstrate a strict subtype relationship and can be used interchangeably, unless solving your problem requires that they be used interchangeably. There is no need for an object to make its data available to the rest of the program, unless the problem can be better solved (or cheaper solved, or some other desirable property) by doing so.

I made quite a big deal earlier of the Open-Closed Principle, and its suggestion that the objects we build be “open to modification...