Michael TsaiVerified account

@rosyna Example?

@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.

@mjtsai Fast enumeration. non-fragile instance vars also means unused ivars can be removed from a class definition.

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

@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 …

@mjtsai And many of the older classes (NSMenu, NSView, NSWindow, et cetera) have ivars no longer in use.

@mjtsai In fact, NSWindow got so insane that a new class, NSWindowAuxiliary, was created to hold the additional ivars.

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