title: Swift cannot determine switch clauses being exhaustive
body: <p>This is an artificial problem because I want to learn about swift in more detail.
  The swift compiler complains about the following not being exhaustive.  Surely in the general case, it cannot determine if the case statements are exhaustive.  How best should I
  tell the compiler my list is exhaustive, such as in the following case?</p>
  
  <pre><code>let point = (2, 2) 
  
  switch point {    
      case let (x, y) where x == y:
          println("on the x=y line")
      case let (x, y) where x != y:
          println("somewhere else off x=y line") 
  }
  </code></pre>
  
  <p>Is the only option to add empty default: cases?</p>