Question

I am trying to understand the working of ruby open classes. In particular how does a method gets added to an existing class?

There must be some logic applied to identify if the class already exists.

Can someone please explain the concept.

Thanks in advance.

Answer 1

Class names are constants, so it’s fairly easy to see if a class name already exists:

Object.constants.grep(/Array/) #=> ["Array"]

So if a class is already defined (Object.const_get('Array').is_a? Class) the methods get added to it, otherwise a new class gets defined. To be a bit more precise this happens on the C side of Ruby, but is more or less what it boils down to.