The WriteBarrier class-comment states:

- any methods that potentially modify instance variables will be overriden in this new class. The overridden method stores the original values of the instance variable in temps, then calls the super method, and then compares the current inst var values with the originals. - If the instance variable values have changed, the WriteBarrier will be notified with a send to #modified:, with the object that was modified as the single argument. - For variably-sized classes, #at:put: is also overridden to provide the same notification.

While integrating WriteBarrier into Magma, I noticed my Array test was actually slower than without WriteBarrier. The problem is in WBClassBuilder>>installAtPutOverrides, which do not check whether the value is changed, it signals #modified no matter what.

To demonstrate this:

| a wb | a _ Array with: true. wb _ DirtySetWriteBarrier new. wb add: a. a at: 1 put: true. wb dirtySet includes: a

This script should return false. After loading the attached fix, it will.

Also, I have a question. Are there any caveats to overriding instVarAt:put: to check for a new value as well? The same class-comment says:

- The WriteBarrier is semi-permeable: if you want to modify an object directly without triggering notifications, you can use #instVarAt:put: and #basicAt:put:.

This reduces transparency albeit just a little; and this same permeability could be achieved by temporarily removing from the WriteBarrier. Is there any reason not to do it?

Regards, Chris