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Adopting Swift 3 | GCD and CoreData in Swift 3

2016-08-17: Note that this post covers Xcode 8 beta 3, the current beta 6 is not compatible with the stuff below.

In the past few days I have been busy upgrading my frameworks (SwifterLog, SwifterJSON, SwifterSockets) and application Swiftfire to Swift 3.
Over all, the migrator does a decent job. It is not flawless but does a good enough job to keep the remaining work to a minimum. It took me about 4 days to upgrade the above mentioned packages.
The job is not finished yet, but I do have a -sort of- running application again.

The three issues that took the most manual work for me is the conversion of Foundation types to build-in Swift types (like NSDate -> Data, NSNumber -> Number, etc) , the adaptation of the new GCD implementation and Core Data.

None of these is difficult per se, but it is a new way of doing thing, thus it takes some time figuring things out.

This is what I learned:


Creating a new queue:

let acceptQueue = DispatchQueue(label: "Accept queue", attributes: [.serial, .qosUserInteractive])

Quite nice actually. And you get to specify both the nature (serial/concurrent) and the priority at the same time. Though I would have liked the priorities specified differently (lowest, low, normal, high, highest ?)

To execute work on the queue:

acceptQueue.async() {
    acceptAndDispatch(socket: acceptSocket)

Or you can use the sync() of course.

To time the execution of some work:

let dpt = DispatchTime(uptimeNanoseconds: + UInt64(delta * Double(NSEC_PER_SEC)))
queue.after(when: dpt) { [weak self] in self?.execute() }

Assuming the delta time is the delay in seconds.

I also updated the synchronization away from p_thread_lock to GCD as suggested:

    public class MyClass {
        private var syncQueue = DispatchQueue(label: "MyClass Synch", attributes: [.serial])
        public var aDate: Date? {
            get {
                return syncQueue.sync(execute: { return self._aDate })
            set {
                syncQueue.sync(execute: { self._aDate = newValue })
             private var _aDate: Date

Though I am a little weary about creating a new queue for every instance of 'MyClass', I decided that for now I will simply wait and see if that becomes a problem.

Core Data

The first I noticed is that the choice to use scalar types has been moved from the "Edit -> Create..." dialogue to the Data Model Inspector. This makes it possible to decide on a case-by-case if we want to use scalar types or not. The second thing is that the choice between Swift and Objective-C has also moved: from the "Edit -> Create..." dialogue to the File Inspector.

Also in the Data Model Inspector there is a new "Codegen" selection box. By default it is set to "Manual/None" which is the same behaviour as before. I have tried the other settings, but either the selection criteria is a little buggy or I am doing things wrong. I could not get the automatic code generation to work properly. No biggy, that can wait.

Generating the managed object custom classes uses a different naming strategy now: <myname>+CoreDataProperties.swift (as before) and <myname>+CoreDataClass.swift (replaces <myname>.swift)
I moved my code from <myname>.swift to <myname>+CoreDataClass.swift and have not experienced any problems.
It can occur that an extra file is created, I have already forgotten how its called precisely, but that file will not compile. Simply delete it. I have read elsewhere that this only occurs if no "save" of the object model was made before creating the managed objects.

The only bigger chance I had to make was to replace the creation of NSFecthRequest's. That must now be done as follows:

let fetchDomainsRequest = NSFetchRequest<CDDomains>(entityName: "CDDomains")

Also, executing the fetch request is now simpeler:

let domainsArray = try self.managedObjectContext.fetch(fetchDomainsRequest)

No need for type casting, that is now implicit.

While there is a new way to create entities as well, that seems to depend on MacOS 10.12, so I kept the old method.

Happy coding...

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