Make a protocol conform to another protocol : <p>I have two protocols: <em>Pen</em> and <em>InstrumentForProfessional</em>. I'd like to make any <em>Pen</em> to be an <em>InstrumentForProfessional</em>:</p>

<pre><code>protocol Pen {
  var title: String {get}
  var color: UIColor {get}
}

protocol Watch {} // Also Instrument for professional
protocol Tiger {} // Not an instrument

protocol InstrumentForProfessional {
  var title: String {get}
}

class ApplePen: Pen {
  var title: String = "CodePen"
  var color: UIColor = .blue
}

extension Pen: InstrumentForProfessional {} // Unable to make ApplePen an Instument for Professional: Extension of protocol Pen cannot have an inheritance clause

let pen = ApplePen() as InstrumentForProfessional
</code></pre>
