Apple Releases Xcode 4.2

Is this similar to Garbage Collection?

It's better than garbage collection. GC is run-time technology and can have a dramatic negative effect on performance. Furthermore, the performance cannot be relied upon to be constant (CPU usage can spike when the GC is sweeping), and since you don't know beforehand when the GC is doing its business, bugs can be harder to track down (objects may disappear at unknowable times).

ARC is a compile-time technology. It inserts retain, release, and autorelease messages just as you would, then optimizes out redundancies before the binary is built. It simply uses the same well-defined memory management rules that you would except it doesn't make mistakes as a human can. There is no run-time penalty.

The biggest disadvantage for ARC is it can't detect cyclical references like a GC can, and that's why it includes the __weak type identifier. So you need to be a little careful for those situations, but overall it's a better technology than GC, which is why GC in Xcode will be going away in favor of ARC, at some point.

ARC here I come! Good riddance manual memory management (for the most part)!

+1. I <3 ARC, but weak references are critical and the existence of incompatible code is irritating. Hopefully we'll get an SDK which is fully-compatible with ARC in Apple's next OS release, at which point we could make a clean break.

Actually, there are two kinds of weak references: "Safe" weak references that change to nil when the referenced object goes away, and "Unsafe" weak references that don't change to nil automatically. Both are "weak" technically weak references. Both work as "weak" references in 10.6, but the automatic change to nil doesn't happen in 10.6. So you can't rely on that if your code should run on 10.6.

Is this similar to Garbage Collection?

It's not a delta update. A hefty installer instead... (1.68 GB if you have 4.1)

No. It is the same old retain/release/autorelease thing, except that you don't write the statements anymore, but the compiler does it for you. The effects are: 1. Your code will be correct, because the compiler doesn't forget to retain or release an item when it should. 2. Your code may become faster, because the compiler optimizes unneeded retain/release away, implements autorelease pools faster, and uses specialized code instead of Objective-C methods. 3. If you have code that is so convoluted that the compiler can't figure out when to retain/release objects then it doesn't compile and you'll have to fix it. Most likely your code was broken anyway in that case.

Compared to Garbage Collection, your memory footprint will be lower.

just tried. seems the answer is no.

Damn, thanks for checking

*rages* :mad:

Should I continue to download from the Dev Center or grab the App Store version?

I'm not sure if the Lion version is available on on the dev center. I downloaded it from the App Store and it went along fine. My coworker is downloading the SL one from the dev center and it's taking forever.

Yes, ARC with Xcode 4.2 is HUGE for developers. If you are an iOS developer, look into ARC! It will save you from so many headaches from now on.

Yes, iOS 5.0 or greater is required for your binaries to use it.