title: F# Set using custom class
body: <p>I'm trying to use Set operations with a class that I have.  Every instance of this class has a unique ID.  Do I need to implement the System.IComparable interface and if so how would I?</p>
  
  <pre><code>type SomeClass(id : int) =
      member this.ID = id
  
  let someSet = Set.of_list [SomeClass(1); SomeClass(2)]
  let test = someSet.Contains(SomeClass(2))    
  </code></pre>