Foldable.swift

class SmartPhone {
  let inch: Double

  init(inch: Double) {
    self.inch = inch
  }
  
  func call(to: String) {
    print("calling to \(to)")
  }
  func showYoutube() {
    print("Watching Youtube")
  }
}

protocol Foldable {
  var isFolded: Bool { get }
}

class GalaxyFold: SmartPhone, Foldable {
  var idsFolded: Bool = false
}

let galaxyFold = GalaxyFold(inch: 7.3)
galaxyFold.isFolded = true
galaxyFold.isFolded = false