We can create class variables by starting a variable name with two @ symbols. Class variables are attached to entire classes, not just instances of classes, like so:

class MyClass
  @@class_variable
end

Because there’s only one copy of a class variable shared by all instances of a class, we can use them to pull off some cool Ruby tricks. For example, we can use a class variable to keep track of the number of instances of that class we’ve created. Let’s do that now!