Michael Tsai on Twitter: "@rosyna I kind of doubt removing old ivars from view classes makes up for slowing down every ivar access with extra indirection."

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Marcel Weiher ‏@mpweiher 19 Aug 2015

@rosyna In my experience, low-level optimizations add up less than one might hope. @gte
Rosyna Keller ‏@rosyna 19 Aug 2015

@mpweiher @gte I disagree and point to cfprefsd, Objective-C 2.0, pretty much all Foundation/CoreFoundation classes, and Metal as evidence.
Marcel Weiher ‏@mpweiher 19 Aug 2015

@rosyna I don't recall Objective-C 2.0 improving performance much, if at all. Can you refresh my memory? @gte
2 likes
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.

‏@mjtsai

@rosyna I kind of doubt removing old ivars from view classes makes up for slowing down every ivar access with extra indirection.

9:52 AM - 19 Aug 2015

Michael TsaiVerified account

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