Swift 中的 ARC：基础功能和拓展功能

1:49 - ARC Example

class Traveler {
    var name: String
    var destination: String?
}

func test() {
    let traveler1 = Traveler(name: "Lily")
    let traveler2 = traveler1
    traveler2.destination = "Big Sur"
    print("Done traveling")
}

6:37 - Reference Cycle Example

class Traveler {
    var name: String
    var account: Account?
    func printSummary() {
        if let account = account {
            print("\(name) has \(account.points) points")
        }
    }
}

class Account {
    var traveler: Traveler
    var points: Int
}

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    traveler.account = account
    traveler.printSummary()
}

9:05 - Weak Reference Example

class Traveler {
    var name: String
    var account: Account?
    func printSummary() {
        if let account = account {
            print("\(name) has \(account.points) points")
        }
    }
}

class Account {
    weak var traveler: Traveler?
    var points: Int
}

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    traveler.account = account
    traveler.printSummary()
}

10:05 - Accessing an object via weak reference

class Traveler {
    var name: String
    var account: Account?
}

class Account {
    weak var traveler: Traveler?
    var points: Int
    func printSummary() {
        print("\(traveler!.name) has \(points) points")
    }
}

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    traveler.account = account
    account.printSummary()
}

11:14 - Accessing an object via optional binding of weak reference

class Traveler {
    var name: String
    var account: Account?
}

class Account {
    weak var traveler: Traveler?
    var points: Int
    func printSummary() {
         if let traveler = traveler {
            print("\(traveler.name) has \(points) points") 
         }
    }
}

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    traveler.account = account
    account.printSummary()
}

11:45 - Safe techniques for handling weak references - withExtendedLifetime()

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    traveler.account = account
    withExtendedLifetime(traveler) {
        account.printSummary()
    }
}

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    traveler.account = account
    account.printSummary()
    withExtendedLifetime(traveler) {}
}

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    defer {withExtendedLifetime(traveler) {}}
    traveler.account = account
    account.printSummary()
}

12:55 - Safe techniques for handling weak references - Redesign to access via strong reference

class Traveler {
    var name: String
    var account: Account?
    func printSummary() {
        if let account = account {
            print("\(name) has \(account.points) points")
        }
    }
}

class Account {
    private weak var traveler: Traveler?
    var points: Int
}

func test() {
    let traveler = Traveler(name: "Lily")
    let account = Account(traveler: traveler, points: 1000)
    traveler.account = account
    traveler.printSummary()
}

14:20 - Safe techniques for handling weak references - Redesign to avoid weak/unowned reference

class PersonalInfo {
    var name: String
}

class Traveler {
    var info: PersonalInfo
    var account: Account?
}

class Account {
    var info: PersonalInfo
    var points: Int
}

15:23 - Deinitializer Example

class Traveler {
  var name: String
  var destination: String?
  deinit {
    print("\(name) is deinitializing")
  }
}

func test() {
    let traveler1 = Traveler(name: "Lily")
    let traveler2 = traveler1
    traveler2.destination = "Big Sur"
    print("Done traveling")
}

16:10 - Sequencing deinitializer side-effects with external program effects

class Traveler {
    var name: String
    var id: UInt
    var destination: String?
    var travelMetrics: TravelMetrics
    // Update destination and record travelMetrics
    func updateDestination(_ destination: String) {
        self.destination = destination
        travelMetrics.destinations.append(self.destination)
    }
    // Publish computed metrics
    deinit {
        travelMetrics.publish()
    }
}

class TravelMetrics {
    let id: UInt
    var destinations = [String]()
    var category: String?
    // Finds the most interested travel category based on recorded destinations
    func computeTravelInterest()
    // Publishes id, destinations.count and travel interest category
    func publish()
}

func test() {
    let traveler = Traveler(name: "Lily", id: 1)
    let metrics = traveler.travelMetrics
    ...
    traveler.updateDestination("Big Sur")
    ...
    traveler.updateDestination("Catalina")
    metrics.computeTravelInterest()
}

verifyGlobalTravelMetrics()

17:56 - Safe techniques for handing deinitalizer side effects - withExtendedLifetime()

func test() {
    let traveler = Traveler(name: "Lily", id: 1)
    let metrics = traveler.travelMetrics
    ...
    traveler.updateDestination("Big Sur")
    ...
    traveler.updateDestination("Catalina")
    withExtendedLifetime(traveler) {
        metrics.computeTravelInterest()
    }
}

18:31 - Safe techniques for handing deinitalizer side effects - Redesign to limit visibility of internal class details

class Traveler {
    ...
    private var travelMetrics: TravelMetrics
    deinit {
        travelMetrics.computeTravelInterest()
        travelMetrics.publish()
    }
}

func test() {
    let traveler = Traveler(name: "Lily", id: 1)
    ...
    traveler.updateDestination("Big Sur")
    ...
    traveler.updateDestination("Catalina")
}

19:08 - Safe techniques for handling deinitalizer side effects - Redesign to avoid deinitializer side-effects

class Traveler {
    ...
    private var travelMetrics: TravelMetrics
     
    func publishAllMetrics() {
        travelMetrics.computeTravelInterest()
        travelMetrics.publish()
    }

    deinit {
				assert(travelMetrics.published)
    }
}

class TravelMetrics {
    ...
    var published: Bool
    ...
}

func test() {
    let traveler = Traveler(name: "Lily", id: 1)
    defer { traveler.publishAllMetrics() }
    ...
    traveler.updateDestination("Big Sur")
    ...
    traveler.updateDestination("Catalina")
}