class DRb::DRbIdConv

and DRbNameIdConv in sample/name.rb in the full drb distribution.
For alternative mechanisms, see DRb::TimerIdConv in drb/timeridconv.rb
within the server runtime.
drb remains valid only while that object instance remains alive
__id__ as its id. This means that an object’s identification over
This, the default implementation, uses an object’s local ObjectSpace
Class responsible for converting between an object and its id.

def to_id(obj)

object space.
This implementation returns the object's __id__ in the local

Convert an object into a reference id. 
def to_id(obj)
  case obj
  when Object
    obj.nil? ? nil : obj.__id__
  when BasicObject
    obj.__id__
  end
end

def to_obj(ref)

space and returns the object it refers to.
This implementation looks up the reference id in the local object

Convert an object reference id to an object. 
def to_obj(ref)
  ObjectSpace._id2ref(ref)
end