SOLVED: Understanding inheritance in child classes

@baggage

Feb '23

I'm coming from a dynamic language background, and struggling to wrap my head around inheritance best practices.

Specifically, I have a ChildClass that I wish to act as a singleton via:

class ChildClass: ParentClass {
  static var myInstance: ChildClass = ChildClass
  private init() {}
}

It overrides:

class ParentClass: ParentClassProtocol, Identifiable, Encodable {
  static var myInstance: ParentClass = ParentClass()
  private init() {}
  // ...lotsa of other methods & variables....
}

The ChildClass 'myInstance' returns a 'cannot override with a stored property 'myInstance' error

From what I understand, the agreed way to get around this is to implement ChildClass and ParentClass by a common protocol, and have ChildClass inherit from ParentClassProtocol instead of ParentClass.

I'm happy to do that, except ParentClassProtocol has a lot of methods that would have duplicate logic in ChildClass...which would be a pretty egregious violation of DRY principles and cause headaches should I forget to change the code in both places in the future.

I suspect I'm misunderstanding best practices here relating to protocols, but I can't figure out how. So in short:

If you had a ParentClass and a ChildClass, and you wanted to ensure different default values for a common declared variable, what are best practices? (And if it's protocols, how do you avoid duplicating all other variables/functions in the method?'

@bobstern

Feb '23

class Parent:  Identifiable, Encodable {
    init() { }
    func who(){print("PARENT")}
    // ...lots of other methods & variables....
}

class ParentClone:  Parent {
    static let singleton = ParentClone()
    // No methods or instance variables.
}

class Child: Parent {
    static let singleton = Child()
    override init() { } // Delete if child does not need different init.
    override func who(){print("CHILD")}
}

Child.singleton.who()
ParentClone.singleton.who()

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