Generating Core Data Swift

The Xcode generated NSManagedObject subclasses are annoying me. While they generate as a pair of files where you can add things to the main class and the @NSManaged variables are generated in an extension in a separate file so that they can be be overwritten and replaced as the model is updated without affecting the file where you make your changes unfortunately there is a big deficiency from my point of view in that the model type information does not get fully carried through to the Swift objects.

Insufficiently Typed

There are two generation options, with "Use scalar properties for primitive data types" you get usefully typed integers, floats, doubles and bools but lose the expression to express optionals/nil values. This is presumably due to the limitations of the Objective-C based API. It also expresses date types as NSTimeIntervals (Doubles) rather than NSDates.  The other option will generate with objects so you will get NSDates but for number values and Booleans you will get NSNumbers which lose information about whether it is a floating point type, integer or boolean.

Other Issues

Swift 2 (Xcode 7 GM at least) Generic support for @objc protocols

Just had a response to a radar (thanks Apple Swift team) that you can now implement Objective C protocols with generic Swift classes. This means that you can make typesafe and composable classes to do much of the work for many UI objects without ugly wrapping code and indirection.

This example shows a really basic example and should work in a playground.

In production code I would not initialise the table view cells in the closure but would make the closure but would probably take either the table view as an argument and directly dequeue cells from it or would take the cell as the argument and only configure it in the closure. Still this approach allows much of the boiler plate and common code to be abstracted. The next level may use a similar approach to make each section and an array of such structures could be used to make the whole table (or collection) view.

There is still work for the Swift team to do as I don't think that you can implement the Objective C protocol in an extension to a generic yet. I can't think of a reason why it wouldn't be possible and I'm confident it is coming.

Update: It should work in a protocol. I'm not sure if I'm currently doing something wrong or if it is Swift compiler bug yet:

Swift Performance - iOSDevUK

I presented today at iOSDevUK in Aberystwyth with some more material on Swift Performance and how to profile Swift. Also on wrapping classes in value types. Unfortunately much of the presentation was a demo and there is no video but I'm posting the materials here and will try to make a follow up post covering some more of the details in the next week or two (no promises).

Slides (note that slides a terrible communication mechanism and caveats and subtleties in the talk may be lost):

Unexpected Assertion Behaviour - Radar 21826180

Apologies for the lack of posts, full time work and family time among other things have been keeping me from finishing off Swift performance stuff. The new Swift 2.0 features look really good but again I haven't got stuck in yet. This is a quick post about an issue concerning me since I noticed it when reading Erica Sadun's post about assertions. I actually thought it couldn't be correct when I first read it so unexpected was it but when I checked the documentation it matched exactly what Erica said.

Assertions and Unchecked Builds

I use assertions for things that shouldn't happen but sometimes might. For example corrupt or unprocessable network data where I write code to safely handle the case but I also want to know instantly and start debugging the issue (whether it is in the app or the server). If you do the same and have assertions which could happen then you must not build in -Ounchecked (or in Swift 2.0 with Disable Safety Checks enabled) otherwise in the event of assertions not being true you will be in undefined behaviour.

How Swift is Swift?

Slides, video and links related to my Swift Summit talk on Swift performance. Video should be available later is now available and it might be worth watching Airspeed's talk that preceded mine before watching it when it is available I'm also expecting a blog post from him shortly on his static vs. compile time talk which is also highly relevant to optimisation.

The key point in Swift is that as the compiler gets better there is no need to choose between nice code and fast code. With a little thought and knowledge it is usually possible to get close to the speed of lowish level C code with nice abstractions. Some may say that C++ is there already but I enjoy writing Swift code much more and C++ is hampered by it's C legacy and choices made many years ago (for good reasons) from becoming a truly nice language in my view (non-Nullable by default would be hard to retrofit for example).

There were also many other excellent talks at Swift Summit, and all were at least good. I'm looking forward to watching several again.