I have a class that represents an airplane.  This class has a bunch of data
members: x/y/z positions, x/y/z velocities, pitches, rolls, etc.  What I did
is let the user configure what different attributes the airplane had in a
YAML config file, then have the airplane class read in that file and setup
attr_accessors for each attribute in the file.

I have another object (call it airplane_drawing) that is responsible for
drawing this airplane on the screen.  It needs to have access to some of the
attributes of the airplane, and it needs have some of its own attributes
changed whenever airplane's attributes changes.

What is the best way to get airplane_drawing to be notified whenever some
attribute of airplane is changed?  Should I have a thread (or similar) that
checks the airplane object to see if anything's changed?

I hope I've explained this well enough for people to understand... I feel
like this is a fairly common thing to do, but I'm not sure of the best way
to do it.

Thanks,
Joe