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面向协议的编程

• 扩展协议和默认实现

protocol Record: CustomStringConvertible {
    var wins: Int {get}
    var losses: Int {get}
    
    func winningPercent() -> Double
}

extension Record {
    var description: String {
        return String(format: "Wins: %d  Losses: %d", wins, losses)
    }
    
    var gamePlayed: Int {
        return wins + losses
    }
}

struct BasketballRecord: Record {
    var wins: Int
    var losses: Int
    
    func winningPercent() -> Double {
        return Double(wins) / Double (gamePlayed)
    }
}

let teamRecord = BasketballRecord(wins: 2, losses: 10)
print(teamRecord)

• 面向协议编程

protocol Record: CustomStringConvertible {
    var wins: Int {get}
    var losses: Int {get}
    
    func winningPercent() -> Double
}

extension Record {
    var description: String {
        return String(format: "Wins: %d  Losses: %d", wins, losses)
    }
    
    var gamePlayed: Int {
        return wins + losses
    }
    
    func winningPercent() -> Double {
        return Double(wins) / Double (gamePlayed)
    }
}

protocol Tieable {
    var ties: Int{get}
}

extension Record where Self: Tieable {
    var gamePlayed: Int {
        return wins+ties+losses
    }
    
    func winningPercent() -> Double {
        return Double(wins) / Double (gamePlayed)
    }
}
    
struct BasketballRecord: Record {
    var wins: Int
    var losses: Int
}

struct FootballRecord: Record, Tieable {
    var wins: Int
    var ties: Int
    var losses: Int
}

let footballTeamRecord: FootballRecord = FootballRecord(wins: 3, ties: 2, losses: 1)
footballTeamRecord.winningPercent()  // 0.5

• 协议聚合

func award(one: Prizable & CustomStringConvertible) {
    if one.isPrizable(){
        print("Congratulate!")
    }
}

• 范型约束

func topOne<T: Comparable>(seq: [T]) -> T {
    assert(seq.count > 0)
    return seq.reduce(seq[0]){ max( $0 , $1 ) }
}


func topPirzableOne<T: Comparable & Prizable> (seq: [T]) -> T? {
    return seq.reduce(nil){ ( tmpTop: T? , contender: T) in
        
        guard contender.isPrizable() else{
            return tmpTop
        }
        
        guard let tmpTop = tmpTop else{
            return contender
        }
        
        return max( tmpTop , contender )
    }
}

• 委托模式

protocol TurnBasedGame {
    var turn: Int {get set}
    
    func play()
}

protocol TurnBasedGameDelegate {
    func gameStart()
    func playerMove()
    func gameEnd()
    func gameOver() -> Bool
}

class SinglePlayerTurnBasedGame: TurnBasedGame {
    var turn: Int = 0
    var delegate: TurnBasedGameDelegate!
    
    func play() {
        delegate.gameStart()
        while !delegate.gameOver() {
            print("Round ",self.turn)
            delegate.playerMove()
            turn += 1
        }
        delegate.gameEnd()
    }
}


class RollNumberGame: SinglePlayerTurnBasedGame, TurnBasedGameDelegate {

    var score = 0
    
    override init() {
        super.init()
        delegate = self
    }
    
    func gameStart() {
        score = 0
        turn = 0
        print("Game Start")
    }
    
    func playerMove() {
        let rollNumber = Int(arc4random())%6 + 1
        score += rollNumber
        print("The score is ", score, "now.")
    }
    
    func gameEnd() {
        print("You win the game in ", turn, "round!")
    }
    
    func gameOver() -> Bool {
        return score >= 100
    }
    
}

let game:RollNumberGame = RollNumberGame()
game.play()

• 可选的协议方法

@objc protocol TurnBasedGameDelegate {
    func gameStart()
    func playerMove()
    func gameEnd()
    
    @objc optional func turnStart()
    
    func gameOver() -> Bool
}