Le Pont est un patron de conception structurel qui scinde la logique métier ou divise de grandes classes dans des hiérarchies de classes séparées qui vont ensuite évoluer indépendamment.
Une de ces hiérarchies (souvent appelée l’abstraction) gardera une référence vers un objet de la seconde hiérarchie (l’implémentation). L’abstraction pourra déléguer certains (parfois la majorité) de ses appels aux objets de l’implémentation. Puisque toutes les implémentations ont une interface commune, elles sont interchangeables à l’intérieur de l’abstraction.
Exemples d’utilisation : Le patron de conception pont est très utile pour gérer les applications multiplateformes, prendre en charge différents types de serveurs de bases de données ou travailler avec plusieurs fournisseurs d’API d’un certain genre (par exemple les plateformes de cloud, réseaux sociaux, etc.).
Identification : Le pont peut être identifié grâce à une distinction très nette entre une entité de contrôle et plusieurs plateformes différentes dont elle dépend.
Les exemples suivants sont disponibles sur le site de
Swift Playgrounds.
Félicitations à
Alejandro Mohamad pour avoir créé la version du Playground.
Exemple conceptuel
Dans cet exemple, nous allons voir la structure du Pont et répondre aux questions suivantes :
Que contiennent les classes ?
Quels rôles jouent-elles ?
Comment les éléments du patron sont-ils reliés ?
Après avoir étudié la structure du patron, vous pourrez plus facilement comprendre l’exemple suivant qui est basé sur un cas d’utilisation réel en Swift.
Example.swift: Exemple conceptuel
import XCTest
/// The Abstraction defines the interface for the "control" part of the two
/// class hierarchies. It holds a reference to an object from the Implementation
/// hierarchy and delegates all of the real work to this object.
class Abstraction {
fileprivate var implementation: Implementation
init(_ implementation: Implementation) {
self.implementation = implementation
}
func operation() -> String {
let operation = implementation.operationImplementation()
return "Abstraction: Base operation with:\n" + operation
}
}
/// You can extend the Abstraction without changing the Implementation classes.
class ExtendedAbstraction: Abstraction {
override func operation() -> String {
let operation = implementation.operationImplementation()
return "ExtendedAbstraction: Extended operation with:\n" + operation
}
}
/// The Implementation defines the interface for all implementation classes. It
/// doesn't have to match the Abstraction's interface. In fact, the two
/// interfaces can be entirely different. Typically the Implementation interface
/// provides only primitive operations, while the Abstraction defines higher-
/// level operations based on those primitives.
protocol Implementation {
func operationImplementation() -> String
}
/// Each Concrete Implementation corresponds to a specific platform and
/// implements the Implementation interface using that platform's API.
class ConcreteImplementationA: Implementation {
func operationImplementation() -> String {
return "ConcreteImplementationA: Here's the result on the platform A.\n"
}
}
class ConcreteImplementationB: Implementation {
func operationImplementation() -> String {
return "ConcreteImplementationB: Here's the result on the platform B\n"
}
}
/// Except for the initialization phase, where an Abstraction object gets linked
/// with a specific Implementation object, the client code should only depend on
/// the Abstraction class. This way the client code can support any abstraction-
/// implementation combination.
class Client {
// ...
static func someClientCode(abstraction: Abstraction) {
print(abstraction.operation())
}
// ...
}
/// Let's see how it all works together.
class BridgeConceptual: XCTestCase {
func testBridgeConceptual() {
// The client code should be able to work with any pre-configured
// abstraction-implementation combination.
let implementation = ConcreteImplementationA()
Client.someClientCode(abstraction: Abstraction(implementation))
let concreteImplementation = ConcreteImplementationB()
Client.someClientCode(abstraction: ExtendedAbstraction(concreteImplementation))
}
}
Output.txt: Résultat de l’exécution
Abstraction: Base operation with:
ConcreteImplementationA: Here's the result on the platform A
ExtendedAbstraction: Extended operation with:
ConcreteImplementationB: Here's the result on the platform B
Analogie du monde réel
Example.swift: Analogie du monde réel
import XCTest
private class BridgeRealWorld: XCTestCase {
func testBridgeRealWorld() {
print("Client: Pushing Photo View Controller...")
push(PhotoViewController())
print()
print("Client: Pushing Feed View Controller...")
push(FeedViewController())
}
func push(_ container: SharingSupportable) {
let instagram = InstagramSharingService()
let facebook = FaceBookSharingService()
container.accept(service: instagram)
container.update(content: foodModel)
container.accept(service: facebook)
container.update(content: foodModel)
}
var foodModel: Content {
return FoodDomainModel(title: "This food is so various and delicious!",
images: [UIImage(), UIImage()],
calories: 47)
}
}
private protocol SharingSupportable {
/// Abstraction
func accept(service: SharingService)
func update(content: Content)
}
class BaseViewController: UIViewController, SharingSupportable {
fileprivate var shareService: SharingService?
func update(content: Content) {
/// ...updating UI and showing a content...
/// ...
/// ... then, a user will choose a content and trigger an event
print("\(description): User selected a \(content) to share")
/// ...
shareService?.share(content: content)
}
func accept(service: SharingService) {
shareService = service
}
}
class PhotoViewController: BaseViewController {
/// Custom UI and features
override var description: String {
return "PhotoViewController"
}
}
class FeedViewController: BaseViewController {
/// Custom UI and features
override var description: String {
return "FeedViewController"
}
}
protocol SharingService {
/// Implementation
func share(content: Content)
}
class FaceBookSharingService: SharingService {
func share(content: Content) {
/// Use FaceBook API to share a content
print("Service: \(content) was posted to the Facebook")
}
}
class InstagramSharingService: SharingService {
func share(content: Content) {
/// Use Instagram API to share a content
print("Service: \(content) was posted to the Instagram", terminator: "\n\n")
}
}
protocol Content: CustomStringConvertible {
var title: String { get }
var images: [UIImage] { get }
}
struct FoodDomainModel: Content {
var title: String
var images: [UIImage]
var calories: Int
var description: String {
return "Food Model"
}
}
Output.txt: Résultat de l’exécution
Client: Pushing Photo View Controller...
PhotoViewController: User selected a Food Model to share
Service: Food Model was posted to the Instagram
PhotoViewController: User selected a Food Model to share
Service: Food Model was posted to the Facebook
Client: Pushing Feed View Controller...
FeedViewController: User selected a Food Model to share
Service: Food Model was posted to the Instagram
FeedViewController: User selected a Food Model to share
Service: Food Model was posted to the Facebook
