Extension for default empty value for optional publisher? - swift

Question

I'm trying to pass in an optional publisher to my view's .onReceive. I don't want to force wrap it like this:
let refreshPublisher: AnyPublisher<Void, Never>?
var body: some View {
Group {
...
}
.onReceive(refreshPublisher!) {...}
}
So I'm passing an empty default value like this:
var body: some View {
Group {
...
}
.onReceive(refreshPublisher ?? Empty<Void, Never>().eraseToAnyPublisher()) {...}
}
This is really verbose and want to add an extension on Optional publishers something like this:
extension Optional where Wrapped == Publisher { // Incorrect syntax, doesn't compile
func orEmpty() -> AnyPublisher<Void, Never> { ... }
}
This way, I can end or doing something like this:
var body: some View {
Group {
...
}
.onReceive(refreshPublisher.orEmpty()) {...}
}
Is something like this possible or a better way to handle optional publishers in non-optional chains?

Answer 1

To your specific question, it's certainly possible. I just wouldn't do it this way.
Note the addition of Combine. before Publisher. There's a type called Optional.Publisher that shadows Combine.Publisher and that's what is causing your error.
extension Optional where Wrapped: Combine.Publisher {
func orEmpty() -> AnyPublisher<Wrapped.Output, Wrapped.Failure> {
self?.eraseToAnyPublisher() ?? Empty().eraseToAnyPublisher()
}
}
Instead of doing it this way, I'd make the default value Empty and not use Optional at all:
let refreshPublisher: AnyPublisher<Void, Never>
init(refreshPublisher: AnyPublisher<Void, Never> = Empty().eraseToAnyPublisher()) {
self.refreshPublisher = refreshPublisher
}
I'd also rework this so that the caller can pass any publisher they want rather than forcing AnyPublisher on them:
let refreshPublisher: AnyPublisher<Void, Never>
init<Refresh>(refreshPublisher: Refresh) where Refresh: Publisher,
Refresh.Output == Void, Refresh.Failure == Never {
self.refreshPublisher = refreshPublisher.eraseToAnyPublisher()
}
init() {
self.init(refreshPublisher: Empty())
}