Singleton in Ruby
Singleton is a creational design pattern, which ensures that only one object of its kind exists and provides a single point of access to it for any other code.
Singleton has almost the same pros and cons as global variables. Although they’re super-handy, they break the modularity of your code.
You can’t just use a class that depends on a Singleton in some other context, without carrying over the Singleton to the other context. Most of the time, this limitation comes up during the creation of unit tests.
Usage examples: A lot of developers consider the Singleton pattern an antipattern. That’s why its usage is on the decline in Ruby code.
Identification: Singleton can be recognized by a static creation method, which returns the same cached object.