title: Cannot convert value of type 'Int' to expected argument type 'Index' (aka 'String.CharacterView.Index')
body: <p>Code:</p>
  
  <pre><code>let x: String = ("abc".substringFromIndex(1))
  print(x)
  //func tail(s: String) -&gt; String {
  //    return s.substringFromIndex(1)
  //}
  //print(tail("abcd"))
  </code></pre>
  
  <p>This works as expected. </p>
  
  <p>But if I uncomment the last 4 lines, then I get:</p>
  
  <pre><code>Error: cannot convert value of type 'Int' to expected argument type 'Index' (aka 'String.CharacterView.Index')
  </code></pre>
  
  <p>Really weird. </p>