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?
Use protocol extension with where clause. It works.
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") } }
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).”
