Question

Does ARC ever inject retain and release calls that you generally wouldn’t see in a non-ARC environment?

For example, explicitly releasing an object from a getter:

- (NSArray *)dummyArray {
     return [[NSArray alloc]init];
}

- (void)useDummyArray {
    NSArray * arr = [self dummyArray];
    //do something with arr
    [arr release]; //unconventional injection of release.
}

Would ARC ever generate a release statement like the code above or would it autorelease the array returned by [self dummyArray];

Answer 1

The beauty of ARC is that you don’t know, or need to know. However, you can give hints to the ARC static analyzer:

 -(NSArray *) dummyArray NS_RETURNS_RETAINED { // this tells ARC that this function returns a retained value that should be released by the callee
      return [[NSArray alloc] init]; 
 } 

 -(NSArray *) otherDummyArray NS_RETURNS_NOT_RETAINED { // this tells ARC that the function returns a non-retained (autoreleased) value, which should NOT be released by the callee.
      return [[NSArray alloc] init];
 }

However, NS_RETURNS_NOT_RETAINED is the default, as long as your function name doesn’t begin with init, in which NS_RETURNS_RETAINED becomes default.

So, in your specific scenario, it will almost always return an autorelease‘d value. One major reason for this is support for interpolation with non-ARC code, which could result in leaks.