Property from UITextInputTraits can't be assigned

Question

I encounter strange compile error when accessing UITextView as object conforming to UITextInputTraits:

protocol MyEditingView:UITextInputTraits where Self: UIView {
}

extension UITextView:MyEditingView {
}

class SomeClass {
  var editingView:MyEditingView = UITextView()
  func someFunc() {
    editingView.autocorrectionType = .no
  }
}

"Cannot assign to property: 'self' is immutable"

But if property is explicitly declared in protocol, without inheriting from UITextInputTraits it is compiled successfully.

protocol MyEditingView where Self: UIView {
  var autocorrectionType: UITextAutocorrectionType { get set }
}

And property declaration is same as in UITextInputTraits.

Swift 4.2, XCode 10.1

Answer 1

autocorrectionType property is optional inside UITextInputTraits but when you declare it explicitly in MyEditingView its no more optional property. I tried making it optional property in MyEditingView and got the same compilation error.