Make any class a super simple publisher with publish() and complete() functions

ExampleSimplePublisher.swift

class Names: SimplePublisher {
  typealias Output = Result<String, Error>
  var subscriptions = [SimpleSubscription<Output, Failure>]()
  let names = ["Alice", "Bob", "Claris", "Doug"]
  
  shoutName() {
    if let name = names.randomElement() {
      publish(.success(name))
    } else {
      assertionFailure("There are def some names in there...")
    }
  }
}

let names = Names()

let _ = names.sink { result in
  print("Sinked a name \(name)")
}

names.shoutName()
names.shoutName()
names.shoutName()
names.shoutName()
names.complete()

SimplePublisher.swift

import Foundation
import Combine
import Synchronized

protocol SimplePublisher: Publisher, Synchronized {
    var subscriptions: [SimpleSubscription<Output, Failure>] { get set }
}

extension SimplePublisher {
    public func receive<S>(subscriber: S) where S : Subscriber, Failure == S.Failure, Output == S.Input {
        let subscription = SimpleSubscription(subscriber: AnySubscriber(subscriber))
        subscriber.receive(subscription: subscription)
        
        sync {
            subscriptions.append(subscription)
        }
    }
    
    func publish(_ output: Output) {
        var subscriptions = [SimpleSubscription<Output, Failure>]()
        
        sync {
            subscriptions = self.subscriptions
        }
        
        for subscription in subscriptions {
            guard let demand = subscription.demand else { continue }
            guard demand > 0 else { continue }
            
            let newDemand = subscription.subscriber.receive(output)
            subscription.request(newDemand)
        }
    }
    
    func complete() {
        complete(.finished)
    }
    
    func complete(_ failure: Failure) {
        complete(.failure(failure))
    }
    
    func complete(_ failure: Subscribers.Completion<Failure>) {
        var subscriptions = [SimpleSubscription<Output, Failure>]()
        
        sync {
            subscriptions = self.subscriptions
            self.subscriptions.removeAll()
        }
        
        for subscription in subscriptions {
            subscription.subscriber.receive(completion: failure)
        }
    }
}

SimpleSubscription.swift

import Foundation
import Combine

class SimpleSubscription<Input, Failure: Error>: Subscription {
    let subscriber: AnySubscriber<Input, Failure>
    var demand: Subscribers.Demand? = nil
    
    init(subscriber: AnySubscriber<Input, Failure>) {
        self.subscriber = subscriber
    }
    
    func request(_ demand: Subscribers.Demand) {
        self.demand = demand
    }
    
    func cancel() {
        self.demand = nil
    }
}