gistfile1.txt

protocol ImageProviderProtocol {
  func image() -> UIImage?
}

class ImageProvider {
 extension ImageProvider: ImageProviderProtocol {
 func image() -> UIImage? {
 return nil
}
}

class SomeOtherClass {
 let imageProvider: ImageProviderProtocol
 
 func returnImage -> UIImage {
  return imageProvider.image()  // <- shouldn't this give an error?
 }
 
 }