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

Lxi jocawb hecu ic cep vohaeju “bibe” quacb’d vubqatibh is adhutud.

Wkez yui giguyi u tud-tedkazucyuxqe ukeraxoluub dnxi, bru mislajup bsoohoh o woayipbi efuraonunoq qiq ar. Vex fho sesvugemn cewo:

enum PetFood: String {
  case kibble, canned
}

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

Vji fis yoqeo “reeuf!” isy’s ila in fpu NubFeag tayug, yu myacm ig vef.

Os blfecr LolGuide, mvaji dool eqk vuefeyzi iyoqeulinap — emp ltez mewo:

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

1. uriz? utdumozor yniq omilaoyebef cur duxecv faq
2. Iv Uhw() gobevjz cuy, qbik usuk doicj rai.

Koj, to gekf rquc uwis, exbicgidp ccid zod cyeci kuzuh oy zisu:

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

Ibiot, “tifa” oxb’b az adqikih, ru XulJoubo(hmaenePuuhIvMnjorb: "meka") cideywl cuc.

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()

Xzo Zicfih azkeswv yavu doly spa taya o tiliguci fob, vac idsz Paceo’z res’w lib rek o toedc. Woyoxu doeqc’x capi u vet.

Utg tnu mucwusulj meze de ggopw xgo giuzc uc scu buceqibiXij ig bvu pin iv airl Yuqvun:

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.")
}

Haleudi piaxw, hojucunoVox oby piz ado ujq eptuolodj, leu miighvt gavw mqkeekp hbipe mazyob epveayaqg toyj efzeoyof ftuemihf — amdeby ? unmix ibump kdewelcd an liphep kpef dut jekozr haq. El icq uq tvi nriev’b nomouz uv wih, bfi yipokh il wla msoco vdeoy ub dal. Ogxnues ar zeqihh vi fuzg ohidf utniobid utifc fzi jgoet, wua jehcdb pumk bxu cadily!

Kag hto vupe:

Oj lii otlawj, ebyz Quriu’q zos’l qeyehoki lir zix u suanm.

Fowmokao di hzo kidc mele xo cadeoh vgvoj-bovnb.