xcode - @autoreleasepool without ARC?

Question

I'm new to Xcode 4.2, and I'm not yet fully up to speed on ARC. However, I did read that @autoreleasepool replaces the manual use of autorelease pools and does some special magic under the hood to play nice with ARC.

Yet, when I start a new project in Xcode 4.2 specifically with the ARC option turned off I still get @autoreleasepool statements in the template code.

What's the deal here?

Answer 1

From http://clang.llvm.org/docs/AutomaticReferenceCounting.html#autoreleasepool:

@autoreleasepool may be used in non-ARC translation units, with equivalent semantics.

and Greg Parker says [1] [2]:

LLVM 3.0's @autoreleasepool { ... } is much faster than NSAutoreleasePool if your deployment target is new enough. No ARC required. (…) always works, but it's faster with deployment target of OS X 10.7 or iOS 5.0.

So you may use @autoreleasepool regardless of ARC, and it’ll be faster than NSAutoreleasePool on OS X v10.7+ and iOS 5.0+.