Demo interview

Question 1 of 8 · Criteria · ~8 min · Memory & ARC

Strong vs weak vs unowned references

00:00

“What is the difference between strong, weak and unowned references? Use the snippet: why is customer declared unowned and not weak?”

swift

final class Customer {
    var card: CreditCard?
}

final class CreditCard {
    unowned let customer: Customer   // why unowned, not weak?
    init(customer: Customer) {
        self.customer = customer
    }
}

Criteria — tap what you hear

Tap a row to cycle: hit → partial → missed → clear

1ARC keeps three counts — strong, unowned, weak — not a single refcount

2Strong means ownership: strong count → 0 runs deinit

3Weak goes through a side table and reads nil after deinit

4Unowned is a direct non-owning pointer — traps if used after deinit

5Usage rule: weak when the target may die first, unowned only with a lifetime guarantee

—0/5 marked

Rating

0/500

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