title: Is there a way to use ConcurrentDictionary.TryUpdate with a lambda expression?
body: <p>I have a simple scenario where I want to update the value of an existing item. Only <a href="http://msdn.microsoft.com/en-us/library/ee378664.aspx">AddOrUpdate</a> method offers a delegate where I can update the old value. However I don't want to  add anything if the key does not exist. Also <a href="http://msdn.microsoft.com/en-us/library/dd287117.aspx">TryUpdate</a> method has no overloads that I can get the old value. Is there a way to do it with current API?</p>
  
  <p>Here's the signature I am looking for:</p>
  
  <pre><code>bool TryUpdate(TKey key, Func&lt;TValue,TValue&gt; updateValueFactory)
  </code></pre>