title: Increment number in Dictionary
body: <p>I have a Dictionary <code>[String:AnyObject]</code> which contains some keys and values.</p>
  
  <p>I want to increment a key to which value is of type Double.</p>
  
  <p>I can do it this way:</p>
  
  <pre><code>let nr = dict["number"] as! Double
  dict["number"] = nr + 10
  </code></pre>
  
  <p>But I dont like that way so Im wondering if there is another way</p>
  
  <p>I tried this:</p>
  
  <pre><code>(dict["number"] as! Double) += 10
  </code></pre>
  
  <p>But that gives me an error:</p>
  
  <blockquote>
    <p>Binary operator '+=' cannot be applied to operands of type '(Double)' and 'Double'</p>
  </blockquote>
  
  <p>Why isn't this working?</p>