title: What happened to the Rx Switch() operator?
body: <p>I am working my way through the Hands-On-Labs for reactive extensions (Rx HOL .NET.pdf) which I downloaded from the data developer center (<a href="http://go.microsoft.com/fwlink/?LinkId=208528" rel="noreferrer">here</a>) a few days ago.</p>
  
  <p>I added these references to my project, using NuGet:</p>
  
  <pre><code>System.Reactive 1.0.10621.0
  
  System.Reactive.Windows.Forms 1.0.10621.0
  </code></pre>
  
  <p>I'm almost done with the labs, but I've hit a snag trying to implement the .Switch() example, Visual Studio can't locate the extension method:</p>
  
  <blockquote>
    <p>'System.IObservable'
    does not contain a definition for
    'Switch' and no extension method
    'Switch' accepting a first argument of
    type
    'System.IObservable'
    could be found (are you missing a
    using directive or an assembly
    reference?)</p>
  </blockquote>
  
  <p>Now I know this Hands On Labs document is out of date, because certain things have been renamed (<code>FromEvent</code> became <code>FromEventPattern</code>) and certain things were removed (<code>RemoveTimeStamp</code>) and this document does not reflect that.  For the life of me I cannot guess what they renamed <code>Switch</code> to be, or figure out what assembly they might have moved it to, or find a comprehensive list of release notes that indicate it was removed.</p>
  
  <p>Anyone know where I can find <code>Switch</code> and what it's current name is?</p>