Task group interview question

Task groups and async let are how you run structured concurrent work. Interviewers ask you to pick the right one and explain why.

async let versus task groups

Use async let when you have a fixed, known number of parallel operations, binding each and awaiting them together. Use withTaskGroup when the number of child tasks is dynamic, for example one per item in a list, adding tasks in a loop and collecting results as they finish. Both are structured, so child tasks cannot outlive the scope.

Getting the details right

In a task group, results can arrive in any order, so collect them into a dictionary keyed by input if order matters. Errors from a throwing group propagate out and cancel remaining children, and you can cap concurrency by limiting how many tasks you add before awaiting. Mentioning these details signals real usage.

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Frequently asked

When would you use a task group over async let?

When the number of concurrent child tasks is dynamic, such as one per element in a collection, rather than a fixed set known at compile time.

Do task group results come back in order?

Not necessarily. They arrive as each child finishes, so key results by their input if you need to reassemble a specific order.