PHP:Dealing with Dependencies
Monday, June 30th, 2008Compositional programming style
In the object oriented programming style, it’s preferable to split functionality out to multiple objects, that can work together to solve a single task. Taken to the extreme, this results in more, but smaller, classes and generally relies less on inheritance and more on composition. In lack of better words, I’ll call this compositional programming style. It’s a style which is usually more prevalent with experienced programmers.
For someone coming from an imperative style of programming, this style can appear abstract and confusing, but the benefits are in the flexibility of the code. If different objects are related through composition, parts can be replaced, without changing the code. This makes it easier to reuse components, and to hook into the code, by providing a wrapper here or there. This is especially useful during testing, since it becomes easier to mock out external dependencies (Such as a database or an smtp server).
There is, however, a dark side to composition — dependencies.
So what is a dependency?
For the sake of this post, I’ll use a rather naïve example. Assume, that we were building an addressbook application. This would feature an entity of type Person. In our code, we might have a class …