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? 命令(行为型模式)

命令模式是一种设计模式，它尝试以对象来代表实际行动。命令对象可以把行动(action) 及其参数封装起来，于是这些行动可以被：

重复多次
取消（如果该对象有实现的话）
取消后又再重做

示例：

protocol DoorCommand {
    func execute() -> String
}

final class OpenCommand: DoorCommand {
    let doors:String

    required init(doors: String) {
        self.doors = doors
    }
    
    func execute() -> String {
        return "Opened \(doors)"
    }
}

final class CloseCommand: DoorCommand {
    let doors:String

    required init(doors: String) {
        self.doors = doors
    }
    
    func execute() -> String {
        return "Closed \(doors)"
    }
}

final class HAL9000DoorsOperations {
    let openCommand: DoorCommand
    let closeCommand: DoorCommand
    
    init(doors: String) {
        self.openCommand = OpenCommand(doors:doors)
        self.closeCommand = CloseCommand(doors:doors)
    }
    
    func close() -> String {
        return closeCommand.execute()
    }
    
    func open() -> String {
        return openCommand.execute()
    }
}

用法

let podBayDoors = "Pod Bay Doors"
let doorModule = HAL9000DoorsOperations(doors:podBayDoors)

doorModule.open()
doorModule.close()

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