DiffableClass.swift

import UIKit

enum MySection: Hashable {
    case items
}

class MyItem: Hashable {
    let identifier = UUID()
    
    var value: String?
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(identifier)
    }
    
    static func == (lhs: MyItem, rhs: MyItem) -> Bool {
        return lhs.identifier == rhs.identifier
    }

}

var item = MyItem()
item.value = "A"

var snapshot = NSDiffableDataSourceSnapshot<MySection, MyItem>()
snapshot.appendSections([.items])
snapshot.appendItems([item], toSection: .items)

print(snapshot.itemIdentifiers.map({ $0.value }))
// prints [Optional("A")]

item.value = "B"
snapshot.reloadItems([item])

print(snapshot.itemIdentifiers.map({ $0.value }))
// prints [Optional("B")]