title: init CBCentralManager: Type of expression is ambiguous without more context
body: <p>Trying to initialize a CBCentralManager in a Swift 4.2 project.
  Get the error shown in comment:</p>
  
  <pre><code>import CoreBluetooth
  
  class SomeClass: NSObject, CBCentralManagerDelegate {
  
      // Type of expression is ambiguous without more context
      let manager: CBCentralManager = CBCentralManager(delegate: self, queue: nil)
  
      // MARK: - Functions: CBCentralManagerDelegate
  
      func centralManagerDidUpdateState(_ central: CBCentralManager) { }
  }
  </code></pre>
  
  <p>If I switch <code>self</code> out for <code>nil</code> the error goes away, so I think I'm missing something important from my conformance to <code>CBCentralManagerDelegate</code>...</p>
  
  <p><strong>Can I use the manager without a delegate; and if not, what do I need to do to resolve the error?</strong></p>