Swift Closure Retain Cycle Management

Context

In the Allegiant mobile app, closures are common in async networking, UI callbacks, and view model bindings. A Mobile Engineer should understand how Swift memory management interacts with closures to prevent leaks.

Core Question

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

Your answer should cover:

1. How closures capture values and references under ARC.
2. How a retain cycle forms between an object and a closure stored by that object or another long-lived object.
3. When to use [weak self] versus [unowned self], and how to safely handle each.
4. How you would reason about common Allegiant app cases, such as network completion handlers, timers, and view controller callbacks.

Scope Guidance

The interviewer expects a practical engineering explanation, not just definitions. You should describe what happens under the hood, show short Swift examples, explain trade-offs, and mention common mistakes such as overusing weak, force-unwrapping self, or assuming every closure creates a cycle.