title: what will happen if assign a weak property to a strong property?
body: <p>In old term, it's about assign a autoreleased property to a retain property. What will happen if do that, something like the following does.</p>
  
  <pre><code>@property(strong, nonatomic) NSString *new;
  
  ... 
  
  NSString *old = [NSString stringWithFormat:@"%@ %@"), @"hello", @"world"];
  new = old;
  </code></pre>