Professional PHP Design Patterns

16.1. Problem and Solution

The Singleton Design Pattern is one of the most used Design Patterns I've seen. This particular architecture type provides leverage to object-oriented design that exists normally only in global and procedural programming. Objects created from the Singleton Design Pattern will normally only allow one instance of themselves to be created. On the initial instantiation, the object stores itself internally. Then, it provides a reference to that stored instance. On each new request for a new object, it simply checks its storage. If it already has an instance of itself, it returns that reference. Otherwise, it follows the new object request detailed previously.

Singletons that allow only one instance of themselves are the most common. They are considered exclusive to the one runtime. They should not be allowed to generate clones of themselves.

Design Patterns are great base blueprints for architecting objects. However, as I keep reiterating, they do provide flexibility. Another type of object that exists restricts the number of copies of itself allowed at any one time. The initial architecture is based on the Singleton Design Pattern but is slightly modified. For example, this object may store up to five instances of itself. If a sixth is requested, it may have to wait or just provide a reference to one of the initial five that was created. This type of architecture is especially useful in queued requests.

Regardless of the type of Singleton being designed, ...