title: How to make an IDisposable object a class variable?
body: <p>I am working with Active Directory using C#. Instantiating the <code>PrincipalContext</code> object seems to be expensive, so I'd like to store one in a class variable.</p>
  
  <p>When using <code>PrincipalContext</code> as a local variable, I can use the convenient <code>using</code> syntax. When storing an <code>IDisposable</code> object in a static variable, how do I ensure the object is properly disposed of?</p>