Using enum for getting/setting value and modification date – Inessential · Swift Structs and valueForKey:

example.playground

import Swift
import Cocoa

// Properties you need as an enum - problem of key value coding is it allows you to type *anything*, typos compile fine.
enum SyncObjectPropertyName {
	case Archived
	case Title
}

// Protocol shared both for local and server
protocol SyncObjectReading {
	var archived: Bool { get }
	var archivedModificationDate: NSDate { get }
	var title: String { get }
	var titleModificationDate: NSDate { get }
	
	// Conveniently returns a tuple of the value and its modification date
	func propertyValueAndModificationDate(propertyName: SyncObjectPropertyName) -> (value: AnyObject, modificationDate: NSDate)
}

// Works on a SyncObjectReading instance, gets a tuple of a value and modification date for a property
func SyncObjectReading_propertyValueAndModificationDate(object: SyncObjectReading, propertyName: SyncObjectPropertyName)  -> (value: AnyObject, modificationDate: NSDate) {
	switch propertyName {
	case .Archived:
		return (object.archived, object.archivedModificationDate)
	case .Title:
		return (object.title, object.titleModificationDate)
	}
}

// Incoming object from server
struct ServerObject: SyncObjectReading {
	var archived: Bool
	var archivedModificationDate: NSDate
	var title: String
	var titleModificationDate: NSDate
	
	func propertyValueAndModificationDate(propertyName: SyncObjectPropertyName) -> (value: AnyObject, modificationDate: NSDate) {
		return SyncObjectReading_propertyValueAndModificationDate(self, propertyName)
	}
}

// Locally stored object
class LocalObject : NSObject, SyncObjectReading {
	var archived: Bool
	var archivedModificationDate: NSDate
	var title: String
	var titleModificationDate: NSDate
	
	init(archived: Bool, archivedModificationDate: NSDate, title: String, titleModificationDate: NSDate) {
		self.archived = archived
		self.archivedModificationDate = archivedModificationDate
		self.title = title
		self.titleModificationDate = titleModificationDate
	}
	
	func propertyValueAndModificationDate(propertyName: SyncObjectPropertyName) -> (value: AnyObject, modificationDate: NSDate) {
			return SyncObjectReading_propertyValueAndModificationDate(self, propertyName)
	}
	
	func setProperty(propertyName: SyncObjectPropertyName, value: AnyObject, modificationDate: NSDate) {
		switch propertyName {
		case .Archived:
			archived = value as Bool
			archivedModificationDate = modificationDate
		case .Title:
			title = value as String
			titleModificationDate = modificationDate
		}
	}
	
	func mergeProperty(propertyName: SyncObjectPropertyName, fromSyncObject syncObject:SyncObjectReading) {
		let selfValueAndDate = self.propertyValueAndModificationDate(propertyName)
		let externalValueAndDate = syncObject.propertyValueAndModificationDate(propertyName)
		
		if selfValueAndDate.modificationDate.timeIntervalSinceReferenceDate < externalValueAndDate.modificationDate.timeIntervalSinceReferenceDate {
			self.setProperty(propertyName, value: externalValueAndDate.value, modificationDate: externalValueAndDate.modificationDate)
		}
	}
}

// Example of accessing properties easily.

let localObjectA = LocalObject(archived: true, archivedModificationDate: NSDate(), title: "Note", titleModificationDate: NSDate())
let serverObjectA = ServerObject(archived: false, archivedModificationDate: NSDate(timeIntervalSinceNow: -60*60*123), title: "Note new title", titleModificationDate: NSDate(timeIntervalSinceNow: 60*60*5))

// Archived
localObjectA.propertyValueAndModificationDate(.Archived)
serverObjectA.propertyValueAndModificationDate(.Archived)

// Title
localObjectA.propertyValueAndModificationDate(.Title)
serverObjectA.propertyValueAndModificationDate(.Title)


// Merging
localObjectA.mergeProperty(.Archived, fromSyncObject: serverObjectA)
localObjectA.mergeProperty(.Title, fromSyncObject: serverObjectA)


localObjectA.archived // Should be the same as server date was earlier
localObjectA.title // Should have changed as server date was later