Rosyna Keller on Twitter: "@mjtsai As long as the 32-bit i386 runtime exists, they can't dump the ivars from the headers, sadly."

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Rosyna Keller ‏@rosyna 19 Aug 2015

@mpweiher @gte Objective-C 2.0 allowed new optimizations to take place that weren't possible before due a backward compatibility requirement
Michael Tsai ‏@mjtsai 19 Aug 2015

@rosyna Example?
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai Things like non-pointer isa (http://www.sealiesoftware.com/blog/archive/2013/09/24/objc_explain_Non-pointer_isa.html …) wouldn't be possible if Class hadn't become opaque.
Rosyna Keller ‏@rosyna 19 Aug 2015

@mjtsai Fast enumeration. non-fragile instance vars also means unused ivars can be removed from a class definition.
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.
1 like
Michael Tsai ‏@mjtsai 19 Aug 2015

@rosyna So why are they still using it now that we have Objective-C 2?

‏@rosyna

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

10:03 AM - 19 Aug 2015

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