Michael Tsai on Twitter: "@rosyna Interesting that they added hash ivar for NSIndexPath. NSStringDrawing is a category so not sure what you are referring to there."

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Michael Tsai ‏@mjtsai 19 Aug 2015

@rosyna Why wouldn't fast enumeration have been possible before? Were there really a lot of unused ivars removed?
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai Fast enumeration requires a lot of compiler support and it just happened to be an Objective-C 2.0 feature. https://www.mikeash.com/pyblog/friday-qa-2010-04-16-implementing-fast-enumeration.html …
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai And many of the older classes (NSMenu, NSView, NSWindow, et cetera) have ivars no longer in use.
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai In fact, NSWindow got so insane that a new class, NSWindowAuxiliary, was created to hold the additional ivars.
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai As NSWindowAuxilary isn't public, Apple can add and remove ivars as needed without having the fragile base class problem.
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Michael Tsai ‏@mjtsai 19 Aug 2015

@rosyna So why are they still using it now that we have Objective-C 2?
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai As long as the 32-bit i386 runtime exists, they can't dump the ivars from the headers, sadly.
Michael Tsai ‏@mjtsai 19 Aug 2015

@rosyna So, again, this is not (yet) an actual performance improvement resulting from Objective-C 2.
1 like
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai While NSWindow may have been good to show the pain of fragile base classes, it may have been bad for an optimization example
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai a better example would be NSStringDrawing, all the Gesture Recognizer classes, NSIndexPath, various NSCollectionView classes

‏@mjtsai

@rosyna Interesting that they added hash ivar for NSIndexPath. NSStringDrawing is a category so not sure what you are referring to there.

10:25 AM - 19 Aug 2015

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