Swift Combine wrapped to be RxSwift-like

swiftcombinewrap.swift

import Foundation
import Combine

// define the observable value type
struct DemoValue {
    var value: String
}

// observable class
class DemoObservable {
    // class to pipe data dadSet event to a completion block
    private class EventPipe {
        var dataBlock: ((_ :DemoValue) -> Void)
        var data: DemoValue? {
            didSet(data) {
                // on didSet, call the dataBlock with the value 
                self.dataBlock(self.data ?? DemoValue(value: ""))
            }
        }
        init(_ dataBlock: @escaping (_ :DemoValue) -> Void) {
            self.dataBlock = dataBlock
        }
    }
    
    // name of the observable notification
    // NOTE: use a UUID if this class will be instantitated more than once
    let name = Notification.Name("DemoObservable")
    
    // reference to the subject so we can post nexts
    let subject: Publishers.Map<NotificationCenter.Publisher, DemoValue?>
    
    // initializer
    init() {
        subject = NotificationCenter.Publisher(center: .default, name: name, object: nil).map{
            (notification) -> DemoValue? in
                return (notification.object as? DemoValue)
        }        
    }
    
    // post a next event
    func next(_ demo: DemoValue) {
        NotificationCenter.default.post(name: name, object: demo)
    }

    // subscribe via completion block
    func subscribe(_ dataBlock: @escaping (_ :DemoValue) -> Void) {
        let evPipe = EventPipe(dataBlock)
        let subscriber = Subscribers.Assign(object: evPipe, keyPath: \.data)
        subject.subscribe(subscriber)
    }    
}

// create an observable
let observable = DemoObservable();

// subscribes
observable.subscribe({
    // process data
    print("A:", $0)
})

observable.subscribe({
    // process data
    print("B:", $0)
})

// publish an events
observable.next(DemoValue(value: "foo"))
observable.next(DemoValue(value: "bar"))