public final class Foo: Object, ResultsControllerElement
{
    //If your class doesn't have a unique identifier yet, do this
    public dynamic var resultsControllerId: String = UUID().uuidString
    
    //If it does, you can do this
    public var resultsControllerId: String {
        return <#id#>
    }
}

import UIKit
import RealmSwift
import BLResultsController

class ViewController: UITableViewController {
    let controller: ResultsController<<#SectionType#>>, <#ElementType#>> = {
        do {
            let realm = <#instantiate your realm#>
            let keyPath = <#the key path to your Element's property to be used as a section#>
            return try ResultsController(
                realm: realm,
                sectionNameKeyPath: keyPath,
                sortDescriptors: [
                    SortDescriptor(keyPath: keyPath)
                ]
            )
        } catch {
            assertionFailure("\(error)")
            //do something about the error
        }
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        controller.setChangeCallback { [weak self] change in
            switch change {
            case .reload(_):
                self?.tableView.reloadData()
            case .sectionUpdate(_, let insertedSections, let deletedSections):
                self?.tableView.beginUpdates()
                insertedSections.forEach { self?.tableView.insertSections($0, with: .automatic) }
                deletedSections.forEach { self?.tableView.deleteSections($0, with: .automatic) }
                self?.tableView.endUpdates()
            case .rowUpdate(_, let insertedItems, let deletedItems, let updatedItems):
                self?.tableView.beginUpdates()
                self?.tableView.insertRows(at: insertedItems, with: .automatic)
                self?.tableView.deleteRows(at: deletedItems, with: .automatic)
                self?.tableView.reloadRows(at: updatedItems, with: .automatic)
                self?.tableView.endUpdates()
            }
        }
        
        controller.setFormatSectionIndexTitleCallback { (section, _) -> String in
            return section
        }
        
        controller.setSortSectionIndexTitles { (sections, _) in
            sections.sort(by: { $0 < $1 })
        }

        controller.start()
    }

    override func numberOfSections(in tableView: UITableView) -> Int {
        return controller.numberOfSections()
    }

    override func tableView(_ tableView: UITableView,
                            numberOfRowsInSection section: Int) -> Int
    {
        return controller.numberOfItems(in: section)
    }

    override func tableView(_ tableView: UITableView,
                            cellForRowAt indexPath: IndexPath) -> UITableViewCell
    {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: <#identifier#>) else {
            fatalError("Did we configure the cell correctly on IB?")
        }
        <#code#>
        return cell
    }
    
    override func tableView(_ tableView: UITableView,
                            titleForHeaderInSection section: Int) -> String?
    {
        return controller.section(at: section)
    }
    
    override func sectionIndexTitles(for tableView: UITableView) -> [String]? {
        return controller.indexTitles()
    }
    
    override func tableView(_ tableView: UITableView,
                            sectionForSectionIndexTitle title: String,
                            at index: Int) -> Int
    {
        return controller.indexPath(forIndexTitle: title).section
    }
}

github "BellAppLab/BLResultsController" ~> 2.1.0

.package(url: "https://github.com/BellAppLab/BLResultsController.git", from: "2.1.0")