AnyAsyncSequence

[tevelee (Laszlo Teveli)]

The problem is about error handling. @hborla summarized it well in the SE-0346 review thread:

@hborla

Currently, the default effect for code that's generic over a rethrowing protocol conformance is throws. If we want the syntax some AsyncSequence<Element> to default to non-throwing, we should not adopt primary associated types for AsyncSequence until there is a way to express that default. This proposal does not include adopting primary associated types in the standard library (that will be a separate proposal and discussion) so this proposal doesn't preclude that either.

See also the Pitch thread of SE-0358:

@lorentey

(1) AsyncSequence and AsyncIteratorProtocol logically ought to have Element as their primary associated type. However, we have ongoing evolution discussions about adding a precise error type to these. If those discussions bear fruit, then the new Error associated type would need to also be marked primary. To prevent source compatibility complications, adding primary associated types to these two protocols is deferred to a future proposal.