Swift override protocol methods in sub classes

Question

I've a base class that implements an extension that conforms to a protocol as below:

protocol OptionsDelegate {
    func handleSortAndFilter(opt: Options)
}

extension BaseViewController: OptionsDelegate {
    func handleSortAndFilter(opt: Options) {
        print("Base class implementation")
    }
}

I've a subclass "InspirationsViewController" that inherits from BaseViewController. And I'm overriding protocol method in the extension as below:

extension InspirationsViewController {
    override func handleSortAndFilter(opt: Options) {
        print("Inside inspirations")
    }
}

I'm getting error when I override "handleSortAndFilter" function in subclass extension: "Declerations in extensions cannot override yet"

But I'm not seeing similar problem when I implemented UITableView datasource and delegate methods.

How to avoid this error?

InspirationsViewController is not a subclass, its an extension. I think you defined it wrong. It should be a class InspirationsViewController: BaseViewController — Hossam Ghareeb
@HossamGhareeb he already said InspirationsViewController is subclass of BaseViewController , this is extension for it. This problem is probably haven't got implemented in Swift, you should do override from main class, extension is for adding more function — Tj3n
In extension we can not override methods of the super class. — Aman Gupta
Please post the class definitions also. The code compiles fine here adding class BaseViewController: UIViewController{} and class InspirationsViewController: BaseViewController {}. — shallowThought
@shallowThought, Class declaration that you mentioned is correct. — Satyam

Igor Bidiniuc Igor Bidiniuc · Accepted Answer · 2016-12-27T11:40:23

Use protocol extension with where clause. It works. But I would not recommend you to have such things in your codebase.

class BaseViewController: UIViewController {

}

extension OptionsDelegate where Self: BaseViewController {
  func handleSortAndFilter(opt: Options) {
    print("Base class implementation")
  }
}

extension BaseViewController: OptionsDelegate {

}

class InsipartionsViewController: BaseViewController {

}

extension OptionsDelegate where Self: InsipartionsViewController {
  func handleSortAndFilter(opt: Options) {
    print("Inspirations class implementation")
  }
}

Swift override protocol methods in sub classes

2 Answers