Core PHP Programming, Third Edition

29.2. Singleton

Singleton is a design pattern that is useful when you want to create an object that should be accessible for different, distinct parts of your application. Especially if this object is supposed to contain large chunks of information, instantiating it over and over again may prove to be extremely inefficient. Instead, if you had a way of sharing the same instance between all of the different parts of the application, it would be ideal. Of course, global variables come to mind, but they require you to manage initialization. That is, you must make sure that nobody erases this variable by mistake, that nobody instantiates another instance of this class, and so forth. Relying on the application code to properly use the infrastructure ...