Protocol Obsessed Programming (Pragma Conference 2016)

Presented at Pragma Conference 2016.

Protocols are awesome: They allow us to decouple our software better. But do we use them enough? Time for an experiment: Let’s use protocols to excess to find out where they improve, and where they diminish our code.

Allergy warning: This talk may contain traces of Swift.

Transcript

1. Protocol Obsessed Programming Pragma Conference 2016 Tammo Freese XING AG
2. Protocols •In Objective-C: only a few protocols •Foundation (iOS 10): 356 classes, 26 protocols •In Swift: way more protocols •Int in Foundation (Swift 3): >=13 protocols
3. Should We Use More Protocols?
4. Should We Use More Protocols? protocol density time
5. Should We Use More Protocols? protocol density time “correct” density
6. Should We Use More Protocols? Current protocol density time “correct” density
7. Should We Use More Protocols? Without Protocols Current protocol density time “correct” density
8. Should We Use More Protocols? Without Protocols Protocol Obsessed! Current protocol density time “correct” density
9. Should We Use More Protocols? Without Protocols Protocol Obsessed! Current protocol density time “correct” density ? ? ?
10. Structure •Example •Without protocols •With protocol obsession •Effects of Protocol Obsessed Programming •Recommendations
11. Example
12. Example • Model for collection view content • Adapter to the data source • Updates between two models • (Perform updates on collection view) DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
13. Example Without Protocols
14. CollectionModel • Model for collection view content DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
15. CollectionModel public struct CollectionModel { public func numberOfItems(in section: Int) -> Int public func cellIdentifier(at indexPath: IndexPath) -> String public func cellModel(at indexPath: IndexPath) -> Any mutating public func addCellWith(identifier: String, model: Any) }
16. DataSourceAdapter • Adapts a CollectionModel to the UICollectionViewDataSource protocol • Configuration of cells by overriding a method CollectionUpdates UICollectionView CollectionModel DataSourceAdapter
17. DataSourceAdapter open class CollectionDataSourceAdapter { public var collectionModel: CollectionModel public let dataSource: UICollectionViewDataSource open func configure(cell: UICollectionViewCell, at indexPath: IndexPath, with model: Any) }
18. Usage (1) class DataSourceAdapter: CollectionDataSourceAdapter { override func configure(cell: UICollectionViewCell, at indexPath: IndexPath, with model: Any) { guard let cell = cell as? Cell, let model = model as? String else { return } cell.text = model } }
19. Usage (2) class ViewController: UICollectionViewController { let adapter: CollectionDataSourceAdapter = DataSourceAdapter() override func viewDidLoad() { super.viewDidLoad() var model = CollectionModel() model.addCellWith(identifier: "Cell", model: "A") adapter.collectionModel = model collectionView?.dataSource = adapter.dataSource } … }
20. CollectionUpdates • Represents the updates between two models • Creation via class extension to CollectionModel • Perform updates on UICollectionView via instance method DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
21. CollectionUpdates public struct CollectionUpdates { let indexPathsForInsertedItems: [IndexPath] let indexPathsForDeletedItems: [IndexPath] let indexPathsForReloadedItems: [IndexPath] let indexPathsForMovedItems: [IndexPath: IndexPath] func performOn(_ collectionView: UICollectionView) } public extension CollectionModel { public func updates(to: CollectionModel) -> CollectionUpdates }
22. Usage (3) var toModel = … collectionView.performBatchUpdates({ let fromModel = self.adapter.collectionModel let updates = fromModel.updates(to: toModel) self.adapter.collectionModel = toModel updates.performOn(collectionView) }, completion: nil)
23. Example:
 Protocol Obsessed Programming
24. Example:
 Protocol Obsessed Programming • Don’t expose types (class/struct/enum), only protocols • Object creation: Via functions
25. CollectionModel • Model for collection view content DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
26. CollectionModel • Model for collection view content • Added: builder protocol • Added: function for creation DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
27. CollectionModel public protocol CollectionModel { func numberOfItems(in section: Int) -> Int func cellIdentifier(at indexPath: IndexPath) -> String func cellModel(at indexPath: IndexPath) -> Any } public protocol CollectionModelBuilder: class { func addCellWith(identifier: String, model: Any) } public func collectionModel(builder: (CollectionModelBuilder) -> Void) -> CollectionModel
28. DataSourceAdapter • Adapts a CollectionModel to the UICollectionViewDataSource protocol • Configuration of cells by overriding a method CollectionUpdates UICollectionView CollectionModel DataSourceAdapter
29. DataSourceAdapter • Adapts a CollectionModel to the UICollectionViewDataSource protocol • Configuration of cells by overriding a method setting a protocol property • Added: function for creation DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
30. DataSourceAdapter public protocol CollectionCellConfigurator { func configure(cell: UICollectionViewCell, at indexPath: IndexPath, with model: Any) } public protocol CollectionDataSourceAdapter: class { var collectionModel: CollectionModel { get set } var cellConfigurator: CollectionCellConfigurator? { get set } var dataSource: UICollectionViewDataSource { get } } public func collectionDataSourceAdapter() -> CollectionDataSourceAdapter
31. Usage (1) (Before) class DataSourceAdapter: CollectionDataSourceAdapter { override func configure(cell: UICollectionViewCell, at indexPath: IndexPath, with model: Any) { guard let cell = cell as? Cell, let model = model as? String else { return } cell.text = model } }
32. Usage (1) (After) struct CellConfigurator: CollectionCellConfigurator { func configure(cell: UICollectionViewCell, at indexPath: IndexPath, with model: Any) { guard let cell = cell as? Cell, let model = model as? String else { return } cell.text = model } }
33. Usage (2) (Before) class ViewController: UICollectionViewController { let adapter: CollectionDataSourceAdapter = DataSourceAdapter() override func viewDidLoad() { super.viewDidLoad() var model = CollectionModel() model.addCellWith(identifier: "Cell", model: "A") adapter.collectionModel = model collectionView?.dataSource = adapter.dataSource } … }
34. Usage (2) (After) class ViewController: UICollectionViewController { let adapter: CollectionDataSourceAdapter = collectionDataSourceAdapter() override func viewDidLoad() { super.viewDidLoad() let model = collectionModel { builder in builder.addCellWith(identifier: "Cell", model: "A") } adapter.collectionModel = model adapter.cellConfigurator = CellConfigurator() collectionView?.dataSource = adapter.dataSource } …
35. CollectionUpdates • Represents the updates between two models • Creation via class extension to CollectionModel • Perform updates on UICollectionView via instance method DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
36. CollectionUpdates • Represents the updates between two models • Creation via class protocol extension to CollectionModel • Perform updates on UICollectionView
 target protocol via instance method added through extension DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
37. CollectionUpdates public struct CollectionUpdates { let indexPathsForInsertedItems: [IndexPath] let indexPathsForDeletedItems: [IndexPath] let indexPathsForReloadedItems: [IndexPath] let indexPathsForMovedItems: [IndexPath: IndexPath] func performOn(_ collectionView: UICollectionView) } public extension CollectionModel { public func updates(to: CollectionModel) -> CollectionUpdates }
38. CollectionUpdates public protocol CollectionUpdates { var indexPathsForInsertedItems: [IndexPath] { get } var indexPathsForDeletedItems: [IndexPath] { get } var indexPathsForReloadedItems: [IndexPath] { get } var indexPathsForMovedItems: [IndexPath: IndexPath] { get } } public extension CollectionUpdates { func performOn(_ target: CollectionUpdatesTarget) } public extension CollectionModel { public func updates(to: CollectionModel) -> CollectionUpdates }
39. CollectionUpdatesTarget public protocol CollectionUpdatesTarget { func insertItems(at indexPaths: [IndexPath]) func deleteItems(at indexPaths: [IndexPath]) func reloadItems(at indexPaths: [IndexPath]) func moveItem(at indexPath: IndexPath, to newIndexPath: IndexPath) } extension UICollectionView: CollectionUpdatesTarget { }
40. Usage (3) (Before) var toModel = … collectionView.performBatchUpdates({ let fromModel = self.adapter.collectionModel let updates = fromModel.updates(to: toModel) self.adapter.collectionModel = toModel updates.performOn(collectionView) }, completion: nil)
41. Usage (3) (After) var toModel = … collectionView.performBatchUpdates({ let fromModel = self.adapter.collectionModel let updates = fromModel.updates(to: toModel) self.adapter.collectionModel = toModel updates.performOn(collectionView) }, completion: nil)
42. Effects of
 Protocol Obsessed Programming
43. Effects of
 Protocol Obsessed Programming • Decoupling • Easier reuse, easier testing
44. Effects of
 Protocol Obsessed Programming • Decoupling • Easier reuse, easier testing • Information hiding • No concrete types exposed
45. Effects of
 Protocol Obsessed Programming • Decoupling • Easier reuse, easier testing • Information hiding • No concrete types exposed • Protocols: no generics possible, but associated types
46. Effects of
 Protocol Obsessed Programming • Decoupling • Easier reuse, easier testing • Information hiding • No concrete types exposed • Protocols: no generics possible, but associated types • Challenge: object creation
47. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
48. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
49. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
50. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
51. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
52. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
53. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
54. Decoupling (Reusability/Testing) Without Protocols Protocol Obsessed DataSourceAdapter CollectionUpdates UICollectionView CollectionModel DataSourceAdapter CollectionUpdates UICollectionView CollectionModel
55. Information Hiding: One Disadvantage DataSourceAdapter CollectionModel Collection View Controller
56. Information Hiding: One Disadvantage DataSourceAdapter CollectionModel Collection View Controller DataSourceAdapter CollectionModel Collection View Controller
57. Information Hiding: One Disadvantage DataSourceAdapter CollectionModel Collection View Controller DataSourceAdapter CollectionModel Collection View Controller =
58. Information Hiding: One Disadvantage DataSourceAdapter CollectionModel Collection View Controller ✓ DataSourceAdapter CollectionModel Collection View Controller =
59. Information Hiding: One Disadvantage DataSourceAdapter CollectionModel Collection View Controller ✓ ✓ DataSourceAdapter CollectionModel Collection View Controller
60. Information Hiding: One Disadvantage • Strong reference cycle possible • Either ignore, or restrict protocol to classes + use weak reference • May require additional property in using class DataSourceAdapter CollectionModel Collection View Controller ✓ ✓ DataSourceAdapter CollectionModel Collection View Controller
61. Recommendations
62. Recommendations • Only expose a concrete type if
63. Recommendations • Only expose a concrete type if • you are 100% sure you don’t want to replace it with a different implementation
64. Recommendations • Only expose a concrete type if • you are 100% sure you don’t want to replace it with a different implementation • you need subclassing (classes)
65. Recommendations • Only expose a concrete type if • you are 100% sure you don’t want to replace it with a different implementation • you need subclassing (classes) • it is your default implementation for a protocol,
 and your protocol obsession only goes so far
66. Should We Use More Protocols?
67. It’s worth a try. Should We Use More Protocols?
68. Questions?