OCP-2.swift

class Circle  {
    var radius: Int
    
    init(radius: Int) {
        self.radius = radius
    }
}

class Rectangle {
    var width: Int
    var height: Int
    
    init(width: Int, height: Int) {
        self.width = width
        self.height = height
    }
}

class AreaCalculator {
    func area(shape: AnyObject) -> Double? {
        if let rectangle = shape as? Rectangle {
            return Double(rectangle.height * rectangle.width)
        } else if let circle = shape as? Circle {
            return Double.pi * Double(circle.radius * circle.radius)
        }
        
        return nil
    }
}