how to loop over instances of a class

fulko.hew_at_sita.aero
Date: 01/30/04 

Date: 30 Jan 2004 11:57:22 -0800

There has got to be a built in way to loop over all instances of a class.
But I can't find it.

ie.

foreach $y (MYCLASS::) {
  $y->mymethod();
}