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.

Simple Library Free JSON Parsing in Swift

Parsing JSON in Swift without adding libraries could be tricky and annoying at least until nil coalescing was added and optional chaining was upgraded late in the original betas but that really isn't the case at least since Swift 1.0 was final. There are clearly a wide range of JSON libraries for Swift ranging from SwiftyJSON which just tidies up extractions from deep in nested structures to Argo which will feel comfortable for those coming from Haskell and look clever but be hard to read for those not familiar with the syntax.

I want to show people that there is really nothing very tricky or ugly about parsing JSON data in Swift even without libraries to help.

This post was trigger by seeing Jameson Quave's new lightweight Luma library and the syntax in the project readme (at the time of writing) would work without a added library on the result of parsing with Cocoa's included NSJSONSerialization class. Please note that there is nothing wrong with the Luma library or anything I have seen written about it but I wanted to make clear how lightweight it is and how easy these things are to do without using a library at all.

I confirmed that the syntax was available in the Playground without using the library and there is no problem just using exactly the same syntax on the dictionary you get back from NSJSONSerialization as in the Luma example. The only difference in the presentation of printing the parsed structures.


Swift 1.2 Update (Xcode 6.3 beta 2) - Performance

Apple have shipped another major update (release notes - registered devs only) only two weeks after shipping the beta 1. There are major updates to Swift Playgrounds, additional syntax support for more flexible `if let`, added a zip function, various other tweaks and fixed a tonne of bugs. This is all on top of the major changes in 1.2 beta 1 that I discussed at Swift London.

Erica Sadun has already blogged about the Playgrounds and `if let` changes and I'm sure that there will be plenty more over the next week. I don't intend to go over that ground but instead discuss the performance changes in Swift 1.2 versions. [Update: I should also have mentioned Jamesson Quave's post that covers the new zip function.]

The performance jumps are very significant in Swift 1.2 and certainly in Beta 2 the steps necessary to optimise your code are significantly changed. This post will cover some information on the improvements and how to get the best out of the Swift compiler. In most cases I have encountered the performance is now very close to C/C++ code and may be faster at times.

Swift 1.2 beta 2 Big Performance News

High performance can be achieved in Xcode 6.3 beta 2 without making code changes to achieve the result that were required to get close previously. Specifically the performance gains of these changes seem to have been largely eliminated:

  1. `final` methods/properties which used to be massive (although I still recommend it where possible for design/safety reasons).
  2. unsafeMutableBuffer instead of array (at least in -Ounchecked builds)
  3. moving code into the same file to allow the compiler to inline (with -whole-module-optimizations build option new in Xcode 6.3 beta 2).

There also seems to have been a slight general performance gain (about 5% above beta 1 from my initial tests).

Is Swift Fast Yet?

Yes. I've always believed that the language had potential to be as fast or faster than C because of strict compile time type checking, immutability and a lack of pointer aliasing concerns. With the Xcode 6.3 betas that promise is being delivered on. I'm sure the work is continuing and there is more to come but it is already fast in most cases. My thanks to the Apple team for making a fast platform but you have just taken away my ability to look impressive by speeding up code significantly with a few simple changes - you bastards.

Swift 1.2 Presentation and Notes (Swift London 17th Feb)

This isn't a proper blog post but I wanted to share the slides and notes from my talk on Swift 1.2 tonight. I'll post a link when the video goes up.  The video is now available here.

One thing that I forgot to mention in the talk is late initialization of let variables. The example Swift 1.2 code does show it though.

Comments, questions and suggestions all welcome.

Slide Text and Notes

Overcoming Swift Resistance Explored

This post is a response to David Owens' Swift Resistance Explored post.

First I want to acknowledge that Swift Debug builds are hideously slow. This isn't news to me or anyone who has seen my talk on Swift optimisation. To be clear this is a problem which Apple have said that they are working on but I still don't think it is an absolute block on any real development because there are fairly simple workarounds.

If you want to see the code under discussion it is all in my repository here with a log of my development. The first commit is the Zipfile that David made available in his blog post, the rest is my testing and development of the Swift version.

These are my performance figures (for 100 runs so it isn't directly comparable to David's):


Obj-C

Swift

Optimised

0.077 (1.8)

0.042 (1)

Debug

0.38 (9.1)

13.7939 (327)

The Importance of Being `final`

[UPDATE - Swift 1.2 from Xcode 6.3 Beta 2 brings performance benefits to non-final properties and methods making final unnecessary for performance from that time - see my initial reaction to Beta 2. I still recommend final where possible as it avoids need to consider effects of an object being subclassed and methods overwritten that change the behaviour.]

This post is intended to quantify, explain and show the performance hit that you take from not adding the word final to your classes (or their properties and methods). The post was triggered by a blog post complaining about Swift performance and showing some performance figures where Swift was significantly slower than Objective-C. In the optimised builds that gap could be closed just by adding a single final keyword. I'm grateful to David Owens for showing the code he was having trouble and giving me a base to demonstrate the difference final can make without it being me cherry picking any code of my choosing.

As with most performance issues this doesn't matter most of the time. Most code is waiting on user input, network responses or other slow things and it really doesn't matter that much if the code is being accessed a few times a second. However when you have got performance critical code and in particular that inner loop that is being executed hundreds of thousands of times a second it can make a huge difference.

What does final do