How does Initialization and class inheritance of function work in Swift

Question

Based on example from JavaScript code I would like to apply the same steps in Swift. If you can help me to understand how it can work to get area of all shapes.

Was trying to solve it with below code, however it does not work.

class Shape {
    func getArea() {
    }
}

class Square: Shape {
    var a: Double
    init(a: Double) {
        self.a = a
        super.init()
    }
    override func getArea() {
        a * a
    }
}

class Rectangle: Shape {
    var a: Double
    var b: Double
    init(a: Double, b: Double) {
        self.a = a
        self.b = b
        super.init()
    }
    override func getArea() {
        a * b
    }
}

class Circle: Shape {
    var r: Double
    init(r: Double) {
        self.r = r
        super.init()
    }
    override func getArea() {
        r * r * Double.pi
    }
}

let square = Square(a: 1.1)
let rectangle = Rectangle(a: 5.0, b: 9.1)
let circle = Circle(r: 2.3)
let shapes = [square, rectangle, circle]

func getTotalArea() -> Double {
    
    let areas = shapes.map { $0.getArea() }
    
    let sum = areas.reduce (1, +)
    
    return sum
}

let shapesArea = getTotalArea()
print(shapesArea)