Ruby can define classes within other classes.
These are called nested classes.
Here's an example:
class Drawing class Line end class Circle end end
Nested classes are defined in the same way as usual. However, they're used differently.
From within Drawing, you can access the Line and Circle classes directly.
From outside the Drawing class, you can only access Line and Circle as Drawing::Line and Drawing::Circle.
class Drawing def Drawing.give_me_a_circle Circle.new # from w w w . j a v a 2 s. c o m end class Line end class Circle def what_am_i "This is a circle" end end end a = Drawing.give_me_a_circle puts a.what_am_i a = Drawing::Circle.new puts a.what_am_i a = Circle.new puts a.what_am_i
a = Drawing.give_me_a_circle calls the give_me_a_circle class method, which returns a new instance of Drawing::Circle.
Next, a = Drawing::Circle.new gets a new instance of Drawing::Circle directly, which also works.