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?

Answer 1

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")
  }
}

Answer 2

As far as I know you can't override methods in extensions. Extensions can only do the following: “Extensions in Swift can:

• Add computed instance properties and computed type properties
• Define instance methods and type methods
• Provide new initializers
• Define subscripts
• Define and use new nested types
• Make an existing type conform to a protocol”

Excerpt From: Apple Inc. “The Swift Programming Language (Swift 3.0.1).”