In VFP, if I needed to instaniate classes of different types I would do something like this:

define class Myclass as session
  worker = null

  proc init(cworker)
     do case
       case cworker = "A"
         this.worker = createobject("ClassA")
       case cworker = "B"
         this.worker = createobject("ClassB")
      endcase
   endproc
enddefine

My problem is that because C# is strongly typed, I don't know how to make worker be an instance of one of several different classes. Any suggestions?