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# next(isolation:)

Produces the next element in the flat map sequence.

```
mutating func next(isolation actor: isolated (any Actor)?) async throws(AsyncFlatMapSequence<Base, SegmentOfResult>.Failure) -> SegmentOfResult.Element?
```

## Discussion

This iterator calls `next(isolation:)` on its base iterator; if this
call returns `nil`, `next(isolation:)` returns `nil`. Otherwise,
`next(isolation:)` calls the transforming closure on the received
element, takes the resulting asynchronous sequence, and creates an
asynchronous iterator from it.  `next(isolation:)` then consumes values
from this iterator until it terminates.  At this point,
`next(isolation:)` is ready to receive the next value from the base
sequence.

---

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