Question

Let’s say that I have a loop that returns a bunch of autoreleased NSData objects…

NSData* bigData = ...
while(some condition) {
    NSData* smallData = [bigData subdataWithRange:...];
    //process smallData
}

Under ARC, should I still wrap an @autoreleasepool around the while condition?

NSData* bigData = ...
@autoreleasepool {
    while(some condition) {
        NSData* smallData = [bigData subdataWithRange:...];
        //process smallData
    }
}

The reason why I’m asking is I see the living allocation count in instruments going through the roof for my NSData objects that invoke a dataWith... method as opposed to an initWith... method. When I use initWith..., the living allocation count is much, much less.

Is it better to prefer the initWith... methods whenever possible?

Answer 1

Yes you should still use autorelease pools when using convenience methods in a tight loop. All the old memory management rules still apply under ARC, the compiler is merely injecting RRs for you. Checkout the great post by the awesome Mike Ash!

Link