OOP Open/Closed principal in Ruby?

Question

Often heard about the Open/Closed principal that says a class should be Open for extension and Closed for modification. Sounds great at the abstract level.

But is there any real-world use-cased example applied in the Ruby OOP land?

Answer 1

Ruby classes are all open. There is no closed class.

Example:

class String
  def foo
    puts "bar"
  end
end

'anything'.foo

#bar