Wednesday, February 11, 2015

Artistic Inheritance

In an earlier post I discussed overloading a method to handle changing it from a computation based on one measurement to having it be based on two. Another way to handle this is with inheritance: you create a new object, say "modernCar," that inherits from myCar and then implements the overload in its method. In this way developers using the old routine use myCar.getCurrentMiles, and developers using the new routine use modernCar.getCurrentMiles.

Using this approach makes more sense than a simple overload when the new way of invoking the method clearly applies to only a selected subset of the base class.

Yet another approach for handling change is to "propertize" the method call. Basically this means changing all of the arguments to the method into class properties instead. To be clear and consistent in this approach the method should place its result in a public property as well, so the sequence for using the new method becomes set miles1, date1, miles2, date2, invoke the method, and get currentMiles.

This approach has the distinct disadvantage that it causes a hard break to existing code. It also requires clearer technical documentation explaining its use. On the other hand this approach has the two distinct advantages that future properties (both set and get) can be added later without impacting the code base, and it also encourages future developers to actually review the target code before invoking the method.

So far then we've seen three approaches for managing change: overload, inheritance, and "propertizing". In a later post I'll discuss your fourth option, deprecation.