Is there a way to "forward" a Publisher through a Subject other than `sink`?

Question

I.e. something equivalent to

extension Publisher {
  func send(_ subject: some Subject<Output, Failure>) -> AnyCancellable {
    sink(
      receiveCompletion: subject.send,
      receiveValue: subject.send
    )
  }
}

Answer 1

There is a subscribe(_:) method which does that.

Here is an example:

private let originalSubject = PassthroughSubject<Void, Never>()
private let myRepublishingSubject = PassthroughSubject<Void, Never>()
private var cancellables: Set<AnyCancellable> = []

originalSubject
   .subscribe(myRepublishingSubject)
   .store(in: &cancellables)
        
myRepublishingSubject
   .sink {
      print("Republished")
   }
   .store(in: &cancellables)

originalSubject.send()

Replace originalSubject with your publisher.

However, this is probably not the best way to use Combine in your code, because Subjects are mostly used as a glue between imperative code and Combine code. Why can't you use the original Publisher directly?