PHP in Action

Chapter 6. Object-oriented principles

6.1	Principles and patterns	103
6.2	The open-closed principle (OCP)	105
6.3	The single-responsibility principle (SRP)	109
6.4	The dependency-inversion principle (DIP)	115
6.5	Layered designs	119
6.6	Summary	122

Once there was a large, heavy, complex web application with lots of modules, bells and whistles, or even timpani and trumpets. It was reasonably successful, but needed to be adapted to a new customer’s needs. The customer needed something with fewer features but with a specific look and feel. The look and feel was well defined: There was an HTML file containing all the styling and layout that was needed.

The existing application had flexibility built in so that a web designer could change the layout ...