A language feature worth understanding

15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.

Use the language note below to explain this example’s state changes. Identify what is copied, what is shared, what can fail, and what is released. Only some of those questions apply to this particular program: say which ones. Make one deliberate change, predict the effect, and compare it with the actual result. A familiar-looking operator in another language may obey a different rule.

let introduces an immutable binding and var a mutable one. Converting text with Int(raw) may produce nil. if let unwraps a present value without force-unwrapping missing data.

let raw = "three"
if let count = Int(raw) {
    print(count)
} else {
    print("Practice")
}

Expected result: Practice

Practice and evidence

Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.

Language reference