Creating a typed-throws AsyncSequence

Using Swift
,
1

Here's a seemingly simple question I can't find an answer to: short of making an ad-hoc implementation of AsyncSequence and AsyncIteratorProtocol, how do I get an async sequence that supports typed throws? AsyncThrowingStream can only be created where Failure == any Error from what I can find, which kind of defeats the purpose of making it generic in the first place.

2

Yep, the stdlib adoption of typed throws is lagging here.

You can easily enough make

struct AsyncTypedThrowsAdapterSequence<Element, Failure: Error>: AsyncSequence { ... }

extension AsyncSequence where Failure == any Error {
    func assertOnlyThrows<E: Error>(
        _ errorType: E.Type
    ) -> AsyncTypedThrowsAdapterSequence<Element, E> { ... }
}

// ...

AsyncThrowingStream(...).assertOnlyThrows(MyErrorType.self)