Actors using Combine

Actor.swift

import Combine
import Foundation

class Actor<Message, State> {
    @Published public private(set) var state: State
    private var cancellables: Set<AnyCancellable>
    let inbox = PassthroughSubject<Message, Never>()
    
    init(initialState: State) {
        state = initialState
        cancellables = []
        inbox.sink { [unowned self] message in
            self.state = self.update(message: message, state: self.state)
        }.store(in: &cancellables)
    }

    func update(message: Message, state: State) -> State {
        return state
    }
}

enum Actors {
    class Counter: Actor<(), Int> {
        override func update(message: (), state: Int) -> Int {
            return state + 1
        }
    }
}