From Java to Swift

LMAX Exchange

Ever since the public beta of OS X I’ve been meaning to get around to learning Objective-C but for one reason or another never found a real reason to. I’ve picked up bits and pieces of it and even written a couple of working utilities but those were pretty much entirely copy/paste from various sources. Essentially they were small enough and short-lived enough that I only needed the barest grasp of Objective-C syntax and no understanding of the core philosophies and idioms that really make a language what it is. This is probably best exemplified by the approach to memory management those utilities took: it won’t run for long, so just let it leak.

I do however have a ton of experience in Java and JavaScript plus knowledge and experience in a bunch of other languages to a wide range of extents. In other words, I’m not a complete moron, I’m just a complete moron with Objective-C.

Anyway, obviously when Swift was announced it was complete justification for my ignoring Objective-C all these years and interesting enough for me to actually get around to learning it.

So I’ve been building a very small little utility in swift so I can pull out information from OS X’s system calendar from the command line and push it around to various places that I happen to want it and can’t otherwise get it. The code is up on GitHub if you’re interested – code reviews and patches most welcome. It’s been a great little project to get used to Swift the language without spending too much time trying to learn all the OS X APIs.

Language Features

Swift has some really nice language features that make dealing with common scenarios simple and clear. Unlike many languages it doesn’t seem to go too far with that though it doesn’t seem likely that people will abuse its features and create overly complex or overly succinct code.

My favourite feature is the built-in optional support. A variable of type String is guaranteed to not be null, a variable of type String? might be. You can’t call any methods from String on a String? variable directly you have to unwrap it first – confirming it isn’t null. That would be painful if it weren’t for the ‘if let’ construct:

let events: String? = ""
if let events = events {
    events.utf16count()
}

I’ve dropped into a habit here which might be a bit overly clever naming the unwrapped variable the same as the wrapped one. The main reason for this is that I can never think of a better name. I figure it’s much like have a if events != nil check.

APIs

Calling Swift a new language is correct but it would almost be more accurate to call it a new syntax instead. Swift does have its own core API which is unique to it, but that’s very limited. For the most part you’re actually dealing with the OS X (or iOS) APIs which are shared with Objective-C. Thus, people with experience developing in Objective-C quite obviously have a huge head start with Swift.

The other impact of sharing so many APIs with Objective-C is that some of the benefits of Swift get lost especially around strict type checking and null reference safety. For example retrieving a list of calendar events is done via the EventKit method:

func eventsMatchingPredicate(predicate: NSPredicate!) -> [AnyObject]!

which is helpfully displayed inside Xcode using Swift syntax despite it being a pre-existing Objective-C API and almost certainly still implemented in Objective-C. However if you look at the return type you see the downside of inheriting the Objective-C APIs: the method documentation says it returns [EKEvent] but the actual declaration is [AnyObject]!  So we’ve lost both type safety and null reference safety because Objective-C doesn’t have non-nullable references or generic arrays. It’s not a massive loss because those APIs are well tested and quite stable so we’re extremely unlikely to be surprised by a null reference or unexpected type in the array, but it does require some casting in our code and requires humans to read documentation and check if something can be null rather than having the compiler do it for us.

If Swift were intended to be a language that competes with Java, python or ruby the legacy of the Objective-C APIs would be a real problem. However, Swift is designed specifically to work with those APIs, to be a relatively small but powerful step of OS X and iOS developers. In that context the legacy APIs are really just a small bump in the road that will smooth out over time.

Xcode

The other really big thing a Java developer notices switching to Swift is what a Java developer notices when switching to any other language – the tools suck. In particular, the Java IDEs are superb these days and make writing, navigating and refactoring code so much easier. Xcode doesn’t even come close. The available refactorings are quite primitive even for C and Objective-C and they aren’t supported at all for Swift.

The various project settings and preferences in Xcode are also a complete mystery and judging from the various questions and explanations on the internet it doesn’t seem to be all that much clearer even to people with lots of experience. In reality I doubt its really much different to Java which also has a ridiculous amount of complexity in IDE settings. The big difference is that in the Java world you (hopefully) start out by learning the basics using the standard command line tools directly. Doing so gives you a good understanding of the build and runtime setup and makes it much clearer what is controlling how your software is built and what is just setting up IDE preferences. Xcode does provide a full suite of command line developer tools so hopefully I can learn more about them and get that basic understanding.

Finally, Xcode 6 beta 3 is horribly buggy. It’s a beta so I can forgive that but I’m surprised at just how bad it is even for a beta.

Cocoa Pods

This was a delight to stumble across.  Adding a dependency to a project was a daunting prospect in Xcode (jar files are surprisingly brilliant). I really don’t know what it did but it worked and I’m grateful. Libraries that aren’t available as pods are pretty much dead to me now. There does seem to be a pretty impressive array of libraries available for a wide range of tasks. Currently all of them are Objective-C libraries so you have to be able to understand Objective-C headers and examples and convert them to Swift but it’s not terribly difficult (and trivial for anyone with an Objective-C background).

Overall

Swift has a good feel about it lots of neat features that keep code succinct. Also it’s very hard not to like strict type checking with good type inference. With Apple pushing Swift as a replacement for Objective-C over time the libraries and APIs will become more and more “Swift-like”. Xcode should improve to at least offer the basic refactorings it has for other languages and stabilise which will make it a workable IDE exceeding the capabilities of what’s available for a lot of languages.

 

Most importantly, the vast majority of existing Objective-C developers seem to quite like it plenty of issues raised as well, but overall generally positive.

I think the future for Swift looks bright.

Adrian Sutton LMAX Exchange Staff Blogs   LMAX Exchange  

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