@autoreleasepool without ARC?

xcode xcode4.2 automatic-ref-counting
fieldtensor picture fieldtensor · Oct 31, 2011 · Viewed 19.7k times · Source

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

user557219 picture user557219 · Oct 31, 2011

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+.

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