Dart 3 incompatibilty: `DelegatingStream<T> extends StreamView` but `StreamView` is `base class` about async HOT 5 CLOSED

The problem comes if someone creates a new interface, say class StreamWithLatest<T> extends Stream<T> { T get latest; bool get hasLatest; StreamWithLatest(Stream<T> source) ... }, which (makes no logical sense, but also) is both an implementation and valid interface that someone can implement in their own way.
(You should never do that! Favor composition over inheritance! But it'll happen.)

If they then decide to use StreamView as an implementation choice,

class StreamWithLatest<T> extends SteamView<T> {
  bool get hasLatest => ...
  T get latest => ...

  StreamWithLatest<T>(super.stream);

  StreamSubscription<T> listen(...) {
    // special implementation
  }
}

then they suddently have to make their StreamWithLatest class base and disallow people from implementing it.
For no good reason.

I'll remove the base from StreamView, and see if I can get it cherry-picked.

from async.

Maybe it was a mistake to make that one base.
Other similar classes have been transformed back to non-base, because it wasn't strictly necessary, and it annoyed subclass authors.

There is no good reason to ever implement StreamView, but it probably also won't hurt anyone but yourself if you do so. Having to write base on all subclasses isn't helping anyone.

from async.

Ah, I hadn't considered how a non-breaking change in the SDK could force down a breaking change on a package like this...

from async.

That type of concern was also the concern that I had shared specifically about class → mixin or mixin class (just because I think it'll be the most widespread).

from async.

Having to write base on all subclasses isn't helping anyone.

I think it helps consumers of DelegatingStream in a similar way to StreamView - it guides towards correct usage.

This class doesn't have any reason to exist anymore in package:async. It would make me a little sad if we have to ship a sub-optimal SDK because of a legacy class in package:async that isn't providing any value to anyone.

I think this class looks like, where it has been used, it's mostly been used correctly. We could check more carefully for usage and add base without a major version bump in this package.

from async.