Optional ni aina (type) ambayo ama inashikilia thamani au inashikilia nil (hakuna thamani). Swift huweka nil wazi ndani ya mfumo wa type: String haiwezi kamwe kuwa nil, lakini String? inaweza. Hivi ndivyo Swift inavyoondoa ajali nyingi za null-pointer wakati wa compile.
Ndani kabisa Int? ni enum yenye cases mbili: .some(value) au .none. Huwezi kutumia thamani iliyofungwa (wrapped) moja kwa moja — lazima uifungue (unwrap) kwanza.
var name: String? = "Ada" // Optional String, currently .some("Ada")
var missing: String? = nil // .none
// if let: bind only when non-nil, scoped to the block
if let name = name {
print(name.count) // safe: name is a plain String here
}
// guard let: unwrap or exit early — keeps the happy path un-nested
func greet(_ input: String?) {
guard let input else { return } // Swift 5.7 shorthand
print("Hi \(input)") // input is non-optional below
}
// nil-coalescing: supply a default
let display = name ?? "Anonymous"
Operator ! hufanya force-unwrap: name! husababisha crash iwapo name ni nil. Itumie tu wakati thamani imehakikishwa na mantiki ya programu — vinginevyo pendelea if let, guard let, au ??.
let url = URL(string: "https://a.com")! // OK: literal is always valid
let user = fetchUser()! // BAD: crashes on nil
String!) hu-crash kimya zinapofikiwa zikiwa nil — jambo la kawaida na @IBOutlet.user?.address?.city hukatiza hadi nil badala ya ku-crash.Optionals husimba "hii inaweza kukosekana" ndani ya type, hivyo compiler inakulazimisha kushughulikia hali ya utupu. Wahojaji hutumia hili kuona kama unatumia guard let na ?? badala ya kusambaza ! kila mahali, ambayo ndiyo tofauti kati ya app inayoelekea crash na ile salama.
Maktaba ya maswali ya mahojiano ya IT yenye majibu ya kina — kutoka Junior hadi Senior.
Changia