Question

I’m trying to understand the difference between the Decorator and Singleton Pattern. For example, in Ruby if I wanted to implement a Singleton Pattern I can use the singleton class. But when I read about the Decorator Pattern in Wikipedia I feel like I would use a singleton class in that case as well.

Answer 1

The Singleton pattern ensures that only one instance (or a limited number of instances) of a class exists at any given time. On the other hand, the Decorator pattern is a mechanism for dynamically adding functionality (responsibilities) to an object, by changing its “skin”. Singleton is a creational pattern, whereas Decorator is a structural pattern.

There really isn’t much in common between the two of them, what’s the source of your confusion? Wait a bit before using Ruby’s Singleton module, better go straight to the original book and understand the fundamental concepts, before thinking about implementation details.