protocol-property-req-explain-4.swift

protocol Flyable {
    
    /// Limit the speed of flyable
    var speedLimit: Int { get set }
    
    func fly()
}

extension Flyable {
    func fly() {
        print("Fly with speed limit: \(speedLimit)mph")
    }
}

class Airplane: Flyable {
    var speedLimit = 500
}

class Helicopter: Flyable {
    var speedLimit = 150
}

class SpeedLimitUpdater {
    
    static func reduceSpeedLimit(of flyables: [Flyable], by value: Int) {
        
        for var flyable in flyables {
            flyable.speedLimit -= value
        }
    }
    
    static func increaseSpeedLimit(of flyables: [Flyable], by value: Int) {
        
        for var flyable in flyables {
            flyable.speedLimit += value
        }
    }
}