Question

I was just reading some source code of https://github.com/MugunthKumar/MKNetworkKit, and saw this

    +(void) initialize {

  if(!_sharedNetworkQueue) {
    static dispatch_once_t oncePredicate;
    dispatch_once(&oncePredicate, ^{
      _sharedNetworkQueue = [[NSOperationQueue alloc] init];
      [_sharedNetworkQueue addObserver:[self self] forKeyPath:@"operationCount" options:0 context:NULL];
      [_sharedNetworkQueue setMaxConcurrentOperationCount:6];

    });
  }            
}

what does that [self self] mean here?

Answer 1

-self is a method defined in the NSObject protocol. It returns the receiver, that is, the object you send the message self to. If you do [a self], you get a back, and yes, if you do [self self] (or self.self), you indeed get self back.

It may be useful in key-value paths where you are supposed to append a new component, but intend to observe the entire object, like in Cocoa Bindings. I don’t see any application of this in the code you posted, but it may be the case that proxies adopt self differently, to point to the proxy itself, rather than the remote/forwarded object.