title: Using __block and __weak
body: <p>I've read over this thread: <a href="https://stackoverflow.com/questions/7080927/what-does-the-block-keyword-mean">What does the &quot;__block&quot; keyword mean?</a> which discusses what <code>__block</code> is used for but I'm confused about one of the answers. It says <code>__block</code> is used to avoid retain cycles, but the comments underneath it leave me unsure.</p>
  
  <p>I'm using it something like this:</p>
  
  <pre><code> self.someProperty = x; //where x is some object (id)
   __block __weak VP_User *this = self;
  
   //begin a callback-style block
       this.someProperty = nil;
  </code></pre>
  
  <p>Do I need to use both <code>__block</code> and <code>__weak</code>? Any glaring problems with this way this looks?</p>