protocol-property-req-explain-full.swift

protocol Flyable {
    
    /// Limit the speed of flyable
    var speedLimit: Int { get }
    
    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) {
        // Only update speedLimit of Helicopter & Airplane
        for flyable in flyables {
            if let helicopter = flyable as? Helicopter {
                helicopter.speedLimit -= value
            } else if let airplane = flyable as? Airplane {
                airplane.speedLimit -= value
            }
        }
        
    }
    
    static func increaseSpeedLimit(of flyables: [Flyable], by value: Int) {
        // Only update speedLimit of Helicopter & Airplane
        for flyable in flyables {
            if let helicopter = flyable as? Helicopter {
                helicopter.speedLimit += value
            } else if let airplane = flyable as? Airplane {
                airplane.speedLimit += value
            }
        }
    }
}

class Bird: Flyable {
    private(set) var speedLimit = 20
}

// Let's test the code above
let flyable1 = Bird()
let flyable2 = Airplane()
let flyable3 = Helicopter()

let flyableArray: [Flyable] = [flyable1, flyable2, flyable3]

SpeedLimitUpdater.reduceSpeedLimit(of: flyableArray, by: 10)
for flyable in flyableArray {
    flyable.fly()
}

a good example in terms of getter and setter according to pop