ARC (Automatic Reference Counting) husimamia kumbukumbu kwa class instances kwa kufuatilia strong references wakati wa compile: compiler huingiza calls za retain/release, na wakati strong count ya object inafikia sifuri hu-deallocated papo hapo — kwa uhakika (deterministically), si kwa background garbage collector.
nil kiotomatiki wakati wa deallocation. Lazima iwe var na optional.unowned(unsafe)).final class Customer {
var card: Card? // strong: customer owns card
}
final class Card {
unowned let owner: Customer // unowned: card never outlives its owner
init(owner: Customer) { self.owner = owner }
}
Chagua kwa uhusiano wa maisha (lifetime), si kwa mazoea:
| weak | unowned | |
|---|---|---|
| Optional | ndiyo (huwa nil) | hapana |
| Gharama ya ARC | juu kidogo (inafuatiliwa) | chini |
| Salama iwapo object nyingine imeenda | ndiyo | crash |
| Tumia wakati | reference inaweza halali kuwa nil (delegates, parent inayoweza kuachiliwa kwanza) | reference imehakikishwa kuishi zaidi ya self (child → parent ya lazima) |
! za rangi ya zambarau huonyesha cycles.deinit logging — ukaguzi wa haraka zaidi: iwapo deinit haichapi kamwe skrini inapofungwa, object hiyo ilivuja.deinit { print("released \(Self.self)") } // silence on dismiss = leak
Escaping closures zinazokamata self, strong references za pande mbili za parent/child, Timer/DispatchSourceTimer zinazoshikilia target yao, na Combine subscriptions ambazo hazijahifadhiwa katika cancellable inayo-deallocate.
ARC ni ya uhakika, hivyo leaks ni jukumu lako, si la GC — view controller moja iliyoshikiliwa inaweza kubandika megabytes za picha na object graph yake yote. Mahojiano ya senior huchunguza hili kwa sababu kuchagua kwa usahihi weak dhidi ya unowned na kujua jinsi ya kuthibitisha leak kwa memory graph ndiko kunakoweka apps za muda mrefu zisivimbe.
Maktaba ya maswali ya mahojiano ya IT yenye majibu ya kina — kutoka Junior hadi Senior.
Changia