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Swift concurrency
async/await interview questions
async/await is the foundation of modern Swift concurrency and a frequent live-coding task. Here is what interviewers ask and how to reason about it.
What gets asked
A very common task is converting a completion-handler API into an async function with withCheckedThrowingContinuation. Interviewers also ask you to run several async calls concurrently with async let or a task group, combine results, and handle errors any child task might throw. Conceptual questions cover how await suspends without blocking a thread.
How to reason about it
Emphasize that await is a suspension point, not a blocking call: the thread is freed while the awaited work runs. Use async let for a fixed set of parallel calls and a task group for a dynamic count. Treat cancellation as cooperative, checking Task.isCancelled or letting CancellationError propagate rather than assuming work stops on its own.
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Frequently asked
How do you convert a completion handler to async/await?
Wrap it with withCheckedContinuation or withCheckedThrowingContinuation, resuming the continuation exactly once inside the completion closure.
async let or task group?
async let suits a fixed, known number of parallel calls; a task group suits a dynamic number of child tasks added and awaited in a loop.