ios - Cannot override method with a custom class return type -

is there method can use override method returns custom class? when tried override method custom class return type, xcode throws me error

below codes:

class customclass {   var name = "myname" }  class parent: uiviewcontroller {    override func viewdidload() {     methodwithnoreturn()     print(methodwithstringasreturn())     methodwithcustomclassasreturn()   }  }  extension parent {    func methodwithnoreturn() { }   func methodwithstringasreturn() -> string { return "parent methodwithreturn" }   func methodwithcustomclassasreturn() -> customclass {     return customclass()   }  }   class child: parent {    override func methodwithnoreturn() {     print("can override")   }    override func methodwithstringasreturn() -> string {     print("cannot override")     return "child methodwithreturn"   }    override func methodwithcustomclassasreturn() -> customclass {     return customclass()   }  } 

the error when overriding method:

func methodwithcustomclassasreturn() -> customclass

with error message:

declarations extensions cannot overridden yet

no reason other compiler doesn't support yet. override method defined in extension superclass, must declare objc-compatible:

extension parent {     func methodwithnoreturn() { }     func methodwithstringasreturn() -> string { return "parent methodwithreturn" }      @objc func methodwithcustomclassasreturn() -> customclass {         return customclass()     }    }  // means must expose customclass objc making inherit nsobject class customclass: nsobject { ... } 

the alternative, without involving objc snafus define these methods in parent class (not inside extension):

class parent: uiviewcontroller {    override func viewdidload() {     methodwithnoreturn()     print(methodwithstringasreturn())     methodwithcustomclassasreturn()   }    func methodwithnoreturn() { }   func methodwithstringasreturn() -> string { return "parent methodwithreturn" }   func methodwithcustomclassasreturn() -> customclass {     return customclass()   }  }