title: Is there some sort of CacheDependency in System.Runtime.Caching?
body: <p>I heard that .NET 4 has a new caching API.</p>
  
  <p>Okay, so the good old <code>System.Web.Caching.Cache</code> (which is, by the way, still there in .NET 4) has the ability to set so-called <code>CacheDependency</code> objects to determine whether a cached item is expired or not.</p>
  
  <p>One can also specify custom logic for determining whether a cached item is still useable or not by deriving a custom subclass from <code>CacheDependency</code>.</p>
  
  <p>I'm curious, is there a way to provide such a logic in the new API?</p>