weak.m

- (void)main {
  __weak id obj;

  // Wrong:
  dispatch_async(queue, ^() {
    [obj doSomething];
    [obj doSomethingElse]; // can turn to nil at any point, should store in strong at beggining of block
    [obj doSomethingElse2];
  });
  
  // Ok:
  __weak id obj;
  dispatch_async(queue, ^() {
    [obj doSomethingAbstract]; // either everything or nothing will execute, no need for strong storage
  });
}

- (void)doSomethingAbstract {
  [self doSomething];
  [self doSomethingElse];
  [self doSomethingElse2];
}