Question

In wikipedia example author has released the object stats, when it has not been allocated, copied, or retained. Is this an error or something I don’t understood?

- (IBAction)analyzeDocument:(NSButton *)sender
{
  dispatch_async(dispatch_get_global_queue(0, 0), ^{
    NSDictionary *stats = [myDoc analyze];
    dispatch_async(dispatch_get_main_queue(), ^{
      [myModel setDict:stats];
      [myStatsView setNeedsDisplay:YES];
      [stats release];
    });
  });
}

Answer 1

It is either an error or it is properly documented that analyze returns ownership of the object to the caller. If it is not an error that stats is released then that codes example is using a convention that goes against Apple’s memory management rules for ownership.

Memory-management rules, sometimes referred to as the ownership
policy, help you to explicitly manage memory in Objective-C code.

You own any object you create by allocating memory for it or copying
it.
Related methods: alloc, allocWithZone:, copy, copyWithZone:,
mutableCopy, mutableCopyWithZone:

Another prefix that should return ownership is the class method +new. E.g. [MyDocClass newAnalysis];