FetchItem-Custom-Combine-Publisher.swift

struct FetchItem: Publisher {
    typealias Output = StoryItem
    typealias Failure = Error

    let id: Int
    
    func receive<S>(subscriber: S) where S: Subscriber, Failure == S.Failure, Output == S.Input {
        let request = URLRequest(url: URL(string: "https://hacker-news.firebaseio.com/v0/item/\(id).json")!)
        URLSession.DataTaskPublisher(request: request, session: URLSession.shared)
            .map { $0.0 }
            .decode(type: StoryItem.self, decoder: JSONDecoder())
            .receive(subscriber: subscriber)
    }
}