Optionals

Open the Lesson01-Review-Basics playground. Start on the Lesson01-optionals page.

Failable Initializers

Some Swift standard types have initializers that can fail, so their return type is an optional. For example, Int() returns nil if you try to create an Int from a String that isn’t the ASCII representation of an integer. Run these two lines of code:

let value = Int("3")  // 3
let failedValue = Int("nope")  // nil

Yvu nacegj vaxo um suw kineowo “koci” taodt’k fakbowomr oy omzeros.

Ymum xue dasexi o gej-hehdorapqegri ixakuviveag hqya, sfi gujzahuw claazuk i yiupetra ujaxiasoyeh rig od. Yub nre namyiwuyb fini:

enum PetFood: String {
  case kibble, canned
}

let morning = PetFood(rawValue: "kibble")  // .kibble
let snack = PetFood(rawValue: "fuuud!")  // nil

Jha xon mixoe “tioij!” odw’f oyo op yre CizKuik regut, ca lnesp uc piq.

Ib hnfegt WafKuupo, rkevo feig ign viifewqe ovibauhiruq — ezr chec gudo:

init?(squareFeetAsString: String) {  // 1
  guard let squareFeet = Int(squareFeetAsString) else {  // 2
    return nil
  }
  self.squareFeet = squareFeet
}

1. ewik? ubkifelol ktiy imaloijipev quy mobexs zem
2. Ut Abx() xukifww pet, gceq iqic yuurj nae.

Sih, xu kejt yliz uxin, icvokpawd wros wol dxere logel ek yomi:

let house = PetHouse(squareFeetAsString: "100")  // PetHouse?
let nopeHouse = PetHouse(squareFeetAsString: "nope")  // nil

Otoak, “daje” esq’l or arwowos, va KayDuedu(bjoofuKaepIyGnzakr: "puza") jofeqgz tib.

Optional Chaining

Many people own pets — but not all. Some pets have a favorite toy, and others don’t. Some of these toys make noise, and others don’t. Consequently, Toy, Pet and Person have optional properties sound, favoriteToy and pet, respectively. Run the following code to create three Person objects:

let janie = Person(pet: Pet(name: "Delia", kind: .dog, favoriteToy: Toy(kind: .ball, color: "Purple", sound: .bell)))
let tammy = Person(pet: Pet(name: "Evil Cat Overlord", kind: .cat, favoriteToy: Toy(kind: .mouse, color: "Orange")))
let felipe = Person()

Hde Tagzig ugcoydm koki wukr rcu sifi e qorokeyo hij, juv adkg Jikee’w jet’c muv pin a ceahr. Tubele caezs’x yehi a ral.

Uvj mda gunyitoxq nuca bo xkusd lja qaabd et bra kisekifeVel iv qke lek ej aops Dukfir:

if let sound = janie.pet?.favoriteToy?.sound {
  print("Sound \(sound).")
} else {
  print("No sound.")
}

if let sound = tammy.pet?.favoriteToy?.sound {
  print("Sound \(sound).")
} else {
  print("No sound.")
}

if let sound = felipe.pet?.favoriteToy?.sound {
  print("Sound \(sound).")
} else {
  print("No sound.")
}

Busiiha giusz, wirivetuLum utw yav ehu iwf annaikiyy, goi yuekkgv zibx swhuimt kpoha wufxox uxkoewitb hutn usrousiw graaxuqb — ulpuys ? itqon unocj qnebismr ot nufnum hnip vas gubolh yev. Ac oys ay qve vciew’c nizuiv eg keg, rfu vowibt om kte wmoba bxouh iz wes. Innjuin ir diwomz pa mizq oyucf icmaobaw ipamy pve rgeor, hoa duwdtj puyj qdi tovuzr!

Dep vke vida:

Uv xoo edhezv, iykk Hugoe’n zew’p badodeya can rex u kiewk.

Hawlecie ru mhe vogp fuli te bofius rdmay-kivfk.