performAction.swift

struct PerformActionSideEffect<Output, Failure: Error> {
  private let publisher: AnyPublisher<Output, Failure>

  init<P: Publisher>(_ publisher: P) where P.Output == Output, P.Failure == Failure {
    self.publisher = publisher.eraseToAnyPublisher()
  }

  @discardableResult
  func performSink(_ action: @escaping (Output) -> Void) -> PerformActionSideEffect {
      publisher.subscribe(
          Subscribers.Sink(receiveCompletion: { _ in }, receiveValue: action)
      )
      return PerformActionSideEffect(publisher)
  }

  @discardableResult
  func performAction(_ action: @escaping () -> Void) -> PerformActionSideEffect {
    performSink { _ in action() }
  }
}

extension Publisher {
    @discardableResult
    func performSink(_ action: @escaping (Output) -> Void) -> PerformActionSideEffect<Output, Failure> {
      return PerformActionSideEffect(self).performSink(action)
    }

    @discardableResult
    func performAction(_ action: @escaping () -> Void) -> PerformActionSideEffect<Output, Failure> {
      PerformActionSideEffect(self).performAction(action)
    }
}