Custom PassthroughSubject, Publisher and Subscriber example

PassthroughSubject.swift

import Combine

enum MyError: Error {
    case subscriberError
}

class StringSubscriber: Subscriber {
    
    func receive(subscription: Subscription) {
        subscription.request(.max(2))
    }
    
    func receive(_ input: String) -> Subscribers.Demand {
        print(input)
        return .max(1)
    }
    
    func receive(completion: Subscribers.Completion<MyError>) {
        print("Completion")
    }
    
    
    typealias Input = String
    typealias Failure = MyError
    
}

let subscriber = StringSubscriber()
        
let subject = PassthroughSubject<String, MyError>()

subject.subscribe(subscriber)

let subscription = subject.sink(receiveCompletion: { (completion) in

    print("Received Completion from sink")

}) { value in

    print("Received Value from sink")
}

subject.send("A")
subject.send("B")

subscription.cancel()

subject.send("C")
subject.send("D")