[Pitch] `Never` as the parameter type for function that does not take a parameter

[gwendal.roue (Gwendal Roué)]

@sveinhal

If SE-0347 gets accepted we could perhaps also use default arguments?

struct PassthroughSubject<Output> {
  func send(_ output: Output = ())
}

That was my initial understanding of SE-0347 initially. Then I changed my mind.