swift - How to make a method in superclass create subclass objects? - 


class car {      func upgrade() -> car {          return car()      } }   class racingcar : car {  }  let racingcar = racingcar() let upgradedracingcar = racingcar.upgrade() // ideally upgradedracingcar should racingcar

how make upgrade method create racingcar objects if called on subclass, without implementing in racingcar?

like this. if it's class method:

class car {     class func upgrade() -> self {          return self()     } }

if it's instance method:

class car {     func upgrade() -> self {          return self.dynamictype()     } }

the return type self means "the class of me, polymorphically". return car if car , racingcar if racingcar. notation self() , self.dynamictype() shorthand calling init; these both classes, that's legal. presume have more elaborate initializer. have make initializer required calm fears of compiler (as explain here); thus, neither of above compile unless init() marked required in car.


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