Swift Closures and Retain Cycles

Context

In the Allegiant Air iOS app, closures are common in async networking, UI callbacks, and view model bindings. Interviewers want to know whether you can reason about memory ownership in Swift and prevent leaks in production code.

Core Question

Explain how you manage memory and avoid retain cycles when using closures in Swift.

Your answer should cover:

1. Why closures can create retain cycles under ARC.
2. How capture lists such as [weak self] and [unowned self] work, and when to use each.
3. What patterns you would use in code for common cases like completion handlers, stored callbacks, and long-lived asynchronous work in the Allegiant Air app.

Scope Guidance

Go beyond saying "use weak self." The interviewer expects you to explain ownership relationships, what happens when self becomes nil, trade-offs between weak and unowned, and common mistakes such as unnecessarily weakening short-lived closures or accidentally crashing with unowned.