Here I could see person.name = newName.text! it changes person.name and I could see the cell text was changed in app. But we don't do anything about data source people, so how it is affected here? Should we write people[indexPath.item].name = newName.text! instead?

    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let person = people[indexPath.item]

        let ac = UIAlertController(title: "Rename person", message: nil, preferredStyle: .alert)
        ac.addTextField()

        ac.addAction(UIAlertAction(title: "Cancel", style: .cancel))

        ac.addAction(UIAlertAction(title: "OK", style: .default) { [unowned self, ac] _ in
            let newName = ac.textFields![0]
            person.name = newName.text!

            self.collectionView?.reloadData()
        })

        present(ac, animated: true)
    }