How to Implement Instance Counters with Class-Level Variables in Ruby?

In Ruby, each class should maintain its own instance count, which can be achieved using class-level instance variables. Class-level instance variables allow different layers of a class hierarchy to maintain their own counters. Class variables, on the other hand, are shared across all instances and subclasses, leading to unexpected results. To implement an instance counter, a class-level instance variable is initialized, and a private setter is defined to ensure it cannot be modified from outside the class hierarchy. A class method is created to increment the instance count safely without exposing the private setter. When an instance of a class is created, it increments the counter for that class only, keeping the counters of other classes independent. Using class-level instance variables and encapsulating their setters privately allows each class to maintain its own instance count without interference from subclasses or external calls. This approach enables the design of clean and efficient class hierarchies. It is not recommended to use class variables instead of class-level instance variables as they share state across the hierarchy, leading to bugs. Private setters are typical when controlling how certain values are manipulated within a class or module.