NotificationCoalescingContext.swift

//
//  NotificationCoalescingContext.swift
//  Created by Christopher Fuller for Southern California Public Radio
//  Original version at https://github.com/SCPR/swift-experiments/blob/master/source/InterfaceUpdatable.swift
//  Updated by Christopher Fuller for Swift 3 compatibility
//
//  Copyright (c) 2016 Southern California Public Radio
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

class NotificationCoalescingContext {

    typealias NotificationPosted<T: ObservableNotification> = (_ observer: NotificationObserver, _ notification: T) -> Void

    private let observer = NotificationObservingContext() // Source: https://git.io/vXl07
    private let queue = NotificationQueue(notificationCenter: NotificationCenter.default)

    @discardableResult func observe<T: ObservableNotification>(_ closure: @escaping NotificationPosted<T>) -> NotificationObserver {
        return observer.observe(object: self) {
            (observer, _, notification: T) in
            closure(observer, notification)
        }
    }

    func removeObservers() {
        observer.removeObservers()
    }

    func enqueue<T: ObservableNotification>(_ notification: T, postingStyle: NotificationQueue.PostingStyle = .asap, coalesceMask: NotificationQueue.NotificationCoalescing? = nil, dequeue: Bool = false) {
        queue.enqueue(notification, object: self, postingStyle: postingStyle, coalesceMask: coalesceMask, dequeue: dequeue)
    }

}

Example Usage

class Example {

    private let coalescer = NotificationCoalescingContext()

    init() {

        // Observe coalesced notification:
        coalescer.observe {
            (observer, notification: ExampleNotification) in
            print(type(of: notification).name)
        }

        // Enqueue notification for coalescing:
        coalescer.enqueue(ExampleNotification())

    }

    deinit {
        // Nothing to do here since the removal of observers occurs automatically when coalescer is deallocated.
    }

}

struct ExampleNotification: ObservableNotification {}

See NotificationObservingContext for information about custom notifications.

And take a look at Apple's NotificationQueue for information about coalescing.