Greetings,
The basic dependency example from "Smalltalk By Example" uses Visualworks changed:with and update:with:from: methods like this:
price: aPrice | oldPrice | oldPrice := self price. price := aPrice. self changed: #price with: oldPrice
update: aSymbol with: oldPrice from: aStock (aSymbol == #price) ifTrue: [Transcript cr; show: thisContext; tab; show: aSymbol; tab; nextPutAll: 'Price changed from: '; show: oldPrice; tab; nextPutAll: 'To: '; show: aStock price; flush]
The problem is that Squeak only implements update:with: so the aStock price messaging doesn't work. My solution was to follow VW's implementation by making the following changes:
Modified the changed:with: method to include from:.
changed: anAspect with: anObject self dependents do: [:aDependent | aDependent update: anAspect with: anObject from: self]
Added an update:with:from: method.
update: anAspect with: anObject from: aSender ^ self update: anAspect with: anObject
It took a while to see the problem and without looking at VW, I never would have been able to figure a way. Is my fix reasonable?
VW also implements expressInterestIn:for:sendBack: and onChangeSend:to: methods. Anyone familiar with them and care to provide pointers on the possibility of implementing something similar in Squeak?
Thanks, Chris