WeatherScene view model. For article: https://medium.com/p/4ddf8710d1a0/

WeatherScene.ViewModel.swift

extension WeatherScene {
    class ViewModel: ObservableObject {
        @Published var city: String = ""
        @Published var countryCode: String = ""
        @Published var system: System = .metric
        @Published var site: Site?
        private var subscribers = Set<AnyCancellable>()
    }
}

extension WeatherScene.ViewModel {
    func fetch() {
        Weather.publisher(
            city: city,
            countryCode: countryCode,
            system: system
        )
        .receive(on: DispatchQueue.main)
        .sink(
            receiveCompletion: { _ in },
            receiveValue: { self.site = $0 }
        )
        .store(in: &subscribers)
    }
}