refactored protocol example

Shape.swift

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

// Base class for inheritance
class Shape {
  var size: CGSize
  func draw(on context: CGContext) { fatalError("override \(#function)") }
  func area() -> CGFloat { return size.width * size.height }
}

// With refactored protocols
protocol Drawable {
  func draw(on context: CGContext)
}

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

// default implementation of area
extension Geometry {
  func area() -> CGFloat { return size.width * size.height }
}