title: How do I get my IEnumerable<T> extension methods on an IEnumerable?
body: <p>I really love using the IEnumerable extension methods. </p>
  
  <p>But sometimes I end up with some collection that only implements IEnumerable and so they aren't available. What is the easiest way to convert the collection to a form where I can use these methods? </p>
  
  <p>And more generally, could someone explain to me exactly what the difference is between these two types and the history behind why these methods exist for the newer IEnumerable?</p>