On Nov 4, 2011, at 10:32 PM, Preston Sumner wrote: > Not if the functions end up sending the message through the runtime anyway, > which is apparently the case._______________________________________________
Since part of the ARC spec requires objects to respond to -retain, -release, and -autorelease (http://clang.llvm.org/docs/AutomaticReferenceCounting.html#objects.retains), this is expected. However, there are still speed gains. For example, in the example posted earlier: Foo *foo = [self foo]; [self doSomethingElse]; [foo bar]; the -foo method will in many cases return an autoreleased object. Under normal memory management, non-ARC, this would end up looking like this: - (Foo *)foo { return [[fooIvar retain] autorelease]; } - (void)bar { Foo *foo = [self foo]; [self doSomethingElse]; [foo bar]; } Upon calling the accessor, retain and autorelease are sent to foo. Sometime later on, foo is sent a release when the autorelease pool is drained, for a total of three message sends. The way I understand it with ARC, though, is that it can peek at the stack to see what will happen to a pointer after it’s returned, and cut out some of the unnecessary message sends, so while it’s actually generating something like this: - (Foo *)foo { return objc_retainAutoreleaseReturnValue(fooIvar); } - (void)bar { Foo *foo = objc_retainAutoreleasedReturnValue([self foo]); [self doSomethingElse]; [foo bar]; objc_release(foo); } in practice, it’s effectively doing something equivalent to this: - (Foo *)foo { return [fooIvar retain]; } - (void)bar { Foo *foo = [self foo]; // -autorelease and -retain cancel each other out here, so they’re both eliminated at runtime [self doSomethingElse]; [foo bar]; [foo release]; } The messages actually sent to foo are retain and release, a total of two message sends; plus, the autorelease pool doesn’t get involved. That’s a win if you ask me. Charles_______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
