title: Swift UIImage extension
body: <p>I am trying to make my code safer using Enums and a connivence initializer when dealing with UIImage and the Asset Catalog.  My code is here below.</p>
  
  <pre><code>import UIKit
  
  extension UIImage {
      enum AssetIdentifier: String {
          case Search = "Search"
          case Menu = "Menu"
      }
  
      convenience init(assetIdentifier: AssetIdentifier) {
          self.init(named: AssetIdentifier.RawValue)
      }
  }
  </code></pre>
  
  <p>Currently I am getting this error.</p>
  
  <pre><code>'Cannot invoke 'UIImage.init' with an argument of type '(named: RawValue.Type)'
  </code></pre>