A singleton class is ideal where you need a single instance to be generated, ensuring that when another object interacts with the class, it will use the same instance as another object. It acts as a better means of accessing data globally within your application, without the risks associated with using $_GLOBALS.

The idea behind using design patterns is to keep your libraries decoupled from one another, allowing you to utilize them in different implementations. A singleton has the same risk associated with it as using global variables in that it may end up tying your classes together, requiring the singleton to be defined across the implementation and making it more difficult to separate it from your application. This may be resolved through the implementation of other design patterns, such as a factory pattern that provides the singleton as an instance into an object, allowing you to replace what you are injecting into the object being instantiated through the factory.

Below is a simple example of how a singleton class is written: