title: How in Swift specify type constraint to be enum?
body: <p>I want to specify a type constraint that the type should be a raw value enum:</p>
  
  <pre><code>enum SomeEnum: Int {
    case One, Two, Three
  }
  
  class SomeProtocol&lt;E: enum&lt;Int&gt;&gt; { // &lt;- won't compile
      func doSomething(e: E) {
          compute(e.toRaw())
      }
  }
  </code></pre>
  
  <p>How can I do it in Swift? (I used the F# syntax for example)</p>