overriding – Can not override with a saved property in Swift

Though there is no technical motive why you can’t override a property with one which introduces storage (though it might increase ambiguities with observer overrides; see this Q&A for more information), Swift would not at the moment permit you to take action.

The truth that in 4.0 you would override a property with a lazy property was unintended (because the override introduces storage), and so you will get a warning in 4.1 and an error in Swift 5 mode with a purpose to protect supply compatibility (applied in #13304).

You may nonetheless obtain the identical end result with a forwarding computed property although:

class A {
  lazy var myVar: String = "A"
}

class B : A {

  // Observe that this is not a particulary compelling case for utilizing 'lazy', as
  // the initialiser expression will not be costly.
  personal lazy var _myVar: String = "B"

  override var myVar: String {
    get { return _myVar }
    set { _myVar = newValue }
  }
}