801: Mainline

Next, you can redefine the update: method such that it responds only to update: messages with specified aspect arguments:

ViewSubclass method definition • instance 
update: aspect 
  aspect = #x 
    ifTrue: 
      [Transcript show: 
        'Sample viewer responding to '  
        , aspect printString 
        , ' update message'; cr.]. 
Workspace
M setX: 0. 
M setY: 1. 
Transcript 
Sample viewer responding to #x update message