class WordCollectionViewController: UICollectionViewController, UICollectionViewLayout {
    // ...
    override func invalidationContext(forInteractivelyMovingItems targetIndexPaths: [IndexPath], withTargetPosition targetPosition: CGPoint, previousIndexPaths: [IndexPath], previousPosition: CGPoint) -> UICollectionViewLayoutInvalidationContext {
            var context = super.invalidationContext(forInteractivelyMovingItems: targetIndexPaths, withTargetPosition: targetPosition, previousIndexPaths: previousIndexPaths, previousPosition: previousPosition)

        return context
    }
}

class ViewController: UIViewController, UITextFieldDelegate {

}

protocol hasAVariablePotato {
   var potato: String! { get set }
}

class PotatoFarmer: Farmer, hasAVariablePotato {

}

class PotatoFarmer: Farmer, hasAVariablePotato {
   var potato: String!
}

import Foundation
import UIKit

class Test:UICollectionViewLayout{

    override func invalidationContext(forInteractivelyMovingItems targetIndexPaths: [IndexPath], withTargetPosition targetPosition: CGPoint, previousIndexPaths: [IndexPath], previousPosition: CGPoint) -> UICollectionViewLayoutInvalidationContext {
        var context = super.invalidationContext(forInteractivelyMovingItems: targetIndexPaths, withTargetPosition: targetPosition, previousIndexPaths: previousIndexPaths, previousPosition: previousPosition)

            return context
    }
}