Vehicle.swift

import UIKit

class Vehicle { //definition..
  var model: String!
  var tires = 4

  func drive() {
  }
  
  func stop() {
  }
}

//subclassing..
var ford = Vehicle() //instance of class Vehicle.
ford.model = "Mustang" // assiging value to a property of class vehicle.
ford.drive()
ford.break()

var BMW = Vehicle()
BMW.model = "7 series"