Question

I fired up irb, and typed:

class Point
end

and then I typed that again, but added some other things.

Irb didn’t complain that I was defining a class that already exists.

Answer 1

In Ruby, you can always add methods to an existing class, even if its a core one:

class String
  def bar
    "bar"
  end
end

"foo".bar # => "bar"

This feature is called “Open Classes.” It’s a great feature, but you should be careful: use it carelessly and you will be patching like a monkey.