How to add the same method to several classes at once?

Question

Swift

I need to add the same method to several classes at once:

class FilterableTable: UITableViewController { ... }
class FilterableCollection: UICollectionViewController { ... }

extension FilterableTable, FilterableCollection { // я знаю, что эта строка некорректна
  func filterItems(){ print('filtered!') }
}

var myTable = FilterableTable()
myTable.filterItems()

var myCollection = FilterableCollection()
myCollection.filterItems()

An extension, as far as I know, cannot be applied to several classes at once.
The protocol only allows you to define method signatures, not the methods themselves.
There is an option with creating a protocol and then extending to it, with a method body. The option seems to be correct, but XCode constantly crashes on it.
The most correct option would be through inheritance, but I can’t figure out how to do this, given that there is no inheritance from several classes in Swift.
I will be grateful for your help!

Answer 1

Finally found an option that looks the most correct: the banal use of delegates.

class FilterableTable: UITableViewController {
    var filterDelegate: FilterDelegate! 
    func viewDidLoad(){
        filterDelegate = Filter()
    }
}
class FilterableCollection: UICollectionViewController {
    var filterDelegate: FilterDelegate! 
    func viewDidLoad(){
        filterDelegate = Filter()
    }
}

protocol FilterDelegate {
    func filterItems()
}

class Filter: FilterDelegate {
    func filterItems() {
        print("Hooray!")
    }
}

Answer 2

You didn't do it right. One of those stories where nails are driven in with a microscope. It turns out that all UIViewControllers will have a filterItems method, about which they will not know anything at all. Correct decision
Announce your protocol

protocol <Name> {
   func filterItems()
}

Implementation for the protocol

extension <Name>  {
   func filterItems(){ print('filtered!') }
}

Well, further in the classes you standardly specify protocol support.
From the bad, your view controller does not do what it should do