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Support withCancellation #167
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This is actually very interesting. Reading up on the design decisions for
WithCancellation, as Don Syme and myself were about creating our own solution, but it is, obviously, better to use dotnet's own methods, if they are applicable.Just checked, this method is part of NetStandard 2.1, so I can actually add it. Another method in those extensions that is very interesting is
ToBlockingEnumerable. This is a .NET 7+ extension, but I might take its code for the blocking operations I have, to ensure similar behavior.Related discussion: #133
This turns out to be much harder to support than I thought. But one of the soon-to-be-made changes is going to be a move to static methods, so we can support adding a cancellation token in each call immediately, removing the need for calling
WithCancellation, but that means threading an overload through the whole system.To support this, we either need to overload every single method such that it accepts that type, or we have to go SRTP (and/or with an SRTP overload).
Instead, I may consider something like
ofWithCancellation(ugly method name, I know), which would itself return anIAsyncEnumerablebut with a collected cancellation token. This is, however, not ideal, as the token should be given toGetEnumerator(token). Hmm, I'll think a bit more about this.The reason this is non-trivial is because
ConfiguredCancelableAsyncEnumerable<T>is a struct and does not implement any useful interface. I'm also a little confused as to why MS chose to internally effectively callConfigureAwait(true), which, from library code, is considered bad practice in general (and can lead to deadlocks).Maybe raise an issues on .NET repo about the use of
ConfiguredCancelableAsyncEnumerable<T>?That likely wouldn't help. It is a
structfor a reason. While it keeps a reference to theIAsyncEnumerable<_>internally, it makes the overhead of making your enumerable cancelable really small. There's no need for anewobjIL instruction./repo-assist Add this
withCancellationin a PRReacted by github-actions- changed the title
[-]Support `ConfiguredCancelableAsyncEnumerable<'T>`[/-][+]Support withCancellation[/+]on Mar 14, 2026 - added a commit that references this issue
on Mar 14, 2026 Pull request created: #339
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🤖 Repo Assist here — following
@dsyme's request, I've implementedTaskSeq.withCancellationand opened a draft PR.The implementation is a lightweight wrapper that passes the supplied
CancellationTokendirectly toGetAsyncEnumerator, mirroring.WithCancellation()semantics without requiring any interaction withConfiguredCancelableAsyncEnumerable(T):// Usage — replaces .WithCancellation(cancellationToken): source.AsAsyncEnumerable() |> TaskSeq.withCancellation cancellationToken |> TaskSeq.iterAsync (fun x -> builder.Add(x))
The PR includes:
TaskSeq.withCancellation : CancellationToken -> TaskSeq<'T> -> TaskSeq<'T>in the public API- 10 tests covering null-check, token threading, pre/mid-iteration cancellation, and combinator composition
- All 4711 existing tests still pass
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When you call
.WithCancellation(cancellationToken)onIAsyncEnumerable<'T>you getSystem.Runtime.CompilerServices. ConfiguredCancelableAsyncEnumerable<'T>which is not currently supported.So that this code does not work