Question

I am reading a book which says (if I am not getting it wrong) wrapping some code with @autoreleasepool statement enables the ARC. First of all is this the case ?

My second concern is when I am doing some iOS example programs, although I enable ARC when creating a new project, I never see this directive being used anywhere (in the automatically generated code). Does this mean that ARC is not being used ? Any ideas/pointers is appreciated.

Answer 1

@autoreleasepool doesn’t “enable” ARC. It’s just the ARC way to use autorelease pools.

Before ARC, you used the NSAutoreleasePool class to set up an autorelease pool like this:

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// Code benefitting from a local autorelease pool.
[pool release];

But you’re not allowed to call release when using ARC, so instead a new way to use autorelease pools was introduced:

@autoreleasepool {
    // Code benefitting from a local autorelease pool.
}

@autoreleasepool blocks are more efficient than using an instance of NSAutoreleasePool directly; you can also use them even if you do not use ARC.