Playground showing how to convert a delegate pattern to combine publishers.

Combine-CLLocationManagerDelegate.swift

//
//  Combine-CLLocationManagerDelegate.playground
//
//  Created by Felix Mau on 30.07.20.
//  Copyright © 2020 Felix Mau. All rights reserved.
//

import PlaygroundSupport
import Combine
import CoreLocation
import Foundation

// Source:
// https://gist.github.com/fxm90/8b6c9753f12fcf19991f6c3f0cd635d3

final class LocationManager: NSObject {

    // MARK: - Public properties

    /// Publisher reporting the latitude, longitude, and course information reported by the system.
    ///
    /// - Note: We hide any details to the underlying publisher by calling `eraseToAnyPublisher()`.
    ///         This makes sure our **public property** is **immutable**.
    ///
    /// - SeeAlso: https://developer.apple.com/documentation/corelocation/cllocation
    var location: AnyPublisher<CLLocation, Error> {
        locationSubject.eraseToAnyPublisher()
    }

    /// Publisher indicating the app's authorization to use location services.
    ///
    /// - Note: We hide any details to the underlying publisher by calling `eraseToAnyPublisher()`.
    ///         This makes sure our **public property** is **immutable**.
    ///
    /// - SeeAlso: https://developer.apple.com/documentation/corelocation/clauthorizationstatus
    var authorizationStatus: AnyPublisher<CLAuthorizationStatus, Never> {
        authorizationStatusSubject.eraseToAnyPublisher()
    }

    // MARK: - Private properties

    /// **Private and mutable** publisher reporting the latitude, longitude, and course information reported by the system.
    private let locationSubject = PassthroughSubject<CLLocation, Error>()

    /// **Private and mutable** publisher indicating the app's authorization to use location services.
    private let authorizationStatusSubject: CurrentValueSubject<CLAuthorizationStatus, Never>

    // MARK: - Dependencies

    private let locationManager: CLLocationManager

    // MARK: - Initializer

    override init() {
        let locationManager = CLLocationManager()
        self.locationManager = locationManager

        authorizationStatusSubject = CurrentValueSubject(locationManager.authorizationStatus)

        super.init()

        locationManager.delegate = self

        // For simplicity we assume that we're authorized to access location data and
        // therefore start location updates immediately.
        locationManager.startUpdatingLocation()
    }

    deinit {
        locationManager.stopUpdatingLocation()
        locationSubject.send(completion: .finished)
    }
}

// MARK: - `CLLocationManagerDelegate` conformance

extension LocationManager: CLLocationManagerDelegate {

    func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
        authorizationStatusSubject.send(status)
    }

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let location = locations.last else {
            // > If updates were deferred or if multiple locations arrived before they could be delivered, the array may contain additional entries.
            // > The objects in the array are organized in the order in which they occurred. Therefore, the most recent location update is at the end
            // > of the array.
            // https://developer.apple.com/documentation/corelocation/cllocationmanagerdelegate/1423615-locationmanager
            return
        }

        locationSubject.send(location)
    }

    func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
        locationSubject.send(completion: .failure(error))
    }
}

Usage example:

let locationManager = LocationManager()
var subscriptions = Set<AnyCancellable>()

locationManager
  .authorizationStatus
  .sink(receiveCompletion: { print("Received completion ", $0) },
        receiveValue: { print("Received value: ", $0) })
  .store(in: &subscriptions)

locationManager
  .location
  .sink(receiveCompletion: { print("Received completion ", $0) },
        receiveValue: { print("Received value: ", $0) })
  .store(in: &subscriptions)