Property Observing: a response to http://inessential.com/2015/08/07/swift_diary_10_changes_to_properties

PropertyObserving.swift

//: Property Observing
// Swift 1.2

import Cocoa
import XCPlayground


protocol ObjectListenerType {
	func objectDidChange<T: AnyObject>(x: T)
}

protocol ModelType: Reflectable {
	typealias Properties
	
	var properties: Properties { get set }
}


class DBStore: ObjectListenerType {
	var foregroundQueue: dispatch_queue_t
	private var pendingObjectIdentifiers = Set<ObjectIdentifier>()
	
	init(foregroundQueue: dispatch_queue_t = dispatch_get_main_queue()) {
		self.foregroundQueue = foregroundQueue
	}
	
	func processChangedObject<T: AnyObject>(x: T) {
		// Only allow objects to be record once
		let identifier = ObjectIdentifier(x)
		if (pendingObjectIdentifiers.contains(identifier)) {
			pendingObjectIdentifiers.remove(identifier)
			
			recordObject(x)
		}
	}
	
	func recordObject<T: AnyObject>(x: T) {
		let mirror = reflect(x)
		for i in 0..<mirror.count {
			let (propertyName, propertyMirror) = mirror[i]
			println(propertyName)
			println(propertyMirror.value)
		}
	}
	
	func objectDidChange<T: AnyObject>(x: T) {
		pendingObjectIdentifiers.insert(ObjectIdentifier(x))
		dispatch_async(foregroundQueue) {
			self.processChangedObject(x)
		}
	}
}

class Model<T>: ModelType {
	typealias Properties = T
	
	let store: ObjectListenerType
	init(store: ObjectListenerType, properties: Properties) {
		self.store = store
		self.properties = properties
	}
	
	var properties: Properties {
		didSet {
			store.objectDidChange(self)
		}
	}
	
	func getMirror() -> MirrorType {
		return reflect(properties)
	}
}



struct Tweet {
	var username: String
	var message: String
	var datePosted: NSDate
}

let store = DBStore()

let tweet = Tweet(username: "brentsimmons", message: "Swift and changes to properties: a feature request. http://inessential.com/2015/08/07/swift_diary_10_changes_to_properties", datePosted: NSDate())
let tweetModel = Model(store: store, properties: tweet)

// Changing two values, which will send two objectDidChange()
// The DBStore will queue, optimally processing the changes once.
tweetModel.properties.message = "Foo bar"
tweetModel.properties.datePosted = NSDate(timeIntervalSinceNow: 200000)


// Allow dispatch_async
XCPSetExecutionShouldContinueIndefinitely()