no override protection example

Geometry.swift

/** 
 * Example from Protocol Oriented Programming - Advanced Swift Programming - raywenderlich.com 
 * https://www.youtube.com/watch?v=ekYdBcl3dzs
 */

protocol Geometry {
  var size: CGSize { get } 
  func boundingBoxArea() -> CGFloat // area -> boundingBoxArea
}

extension Geometry {
  // default implementation means no error raised to Circle
  func boundingBoxArea() -> CGFloat { return size.width * size.height }
}

extension Circle {
  // previous area implementation 
  func area() -> CGFloat { return radius * radius * .pi } 
}