Consider post-update semantics for Shared.publisher

[chuganzy]

Hi! I wanted to ask about the timing semantics of Shared.publisher.

It looks like Shared.publisher currently emits before wrappedValue has been updated. This works when using the emitted value directly:

$count.publisher.sink { count in
  counterLabel.text = "\(count)"
}

But when using the publisher as a change trigger, reading the shared value from an extracted method can observe the previous value:

$count.publisher.sink { [weak self] _ in
  self?.updateLabel()
}

func updateLabel() {
  counterLabel.text = "\(count)" // previous value
}

A similar pattern can come up in a TCA reducer:

case .task:
  return .publisher {
    state.$sort.publisher.map { _ in .reload }
  }
  .cancellable(id: ...)

case .reload:
  switch state.sort { ... } // previous value
  return .none

I saw discussion #128 about accessing the previous value from a publisher. I think that use case can be handled by consumers with scan, whereas this case is about reacting after wrappedValue has already been updated.

Would you consider making Shared.publisher emit after wrappedValue has been updated, or adding a separate post-update/current-value publisher?