Category Archives: Swift

A Tale Of Two Optimizers

I have quipped a few times that my biggest problems with Swift so far have to do with struggles in the debugger. It seems slow, inaccurate, harder to use than in Objective C. Some of this is just a learning curve, but other aspects seemed fundamentally broken. I whined on Twitter about a scenario in which lldb seemed utterly unaware of one of my variables:

A kind Apple employee, Kate Stone, followed up with me and ultimately encouraged me to file a bug:

I obliged, filing Radar #26032843. Today, Apple got back to me with a followup, suggesting rather gently that I may have neglected to disable optimization in my target. Rookie move! The kind of behavior I was seeing in the debugger is exactly what happens when lldb can’t make as much sense of your code because of inlined functions, loops that have been restructured, etc.

In fact, I had correlated the symptoms with such a problem, but when I went to check on the status of my optimization settings, everything looked fine. Why? Because I was looking, by habit, at the Clang LLVM “Code Generation” settings for optimization:

MarsEdit xcodeproj

See? Optimization disabled. Just as it is for all my projects, and all my targets, because I define it once in my centralized Debug “.xcconfig” file, to be sure I never screw it up:

// We only specify an optimization setting for Debug builds.
// We rely upon Apple's default settings to produce reasonable
// choices for Release builds

So why does debugging Swift fail so hard for me? Because Swift doesn’t use that optimization setting. Scrolling down a little farther, I find the culprit in Swift’s own compiler settings section:

MarsEdit xcodeproj

So the lesson is that new Swift developers coming from a legacy of Objective C, C++, or C development need to take stock of Swift compiler settings because they are liable to be rooted in completely different build settings. On the one hand, I’m glad Apple is finally able to get away from a build setting like “GCC_OPTIMIZATION_LEVEL” (though keeping the name in the GCC -> LLVM transition prevented problems like this back then), but on the other hand, it’s kind of annoying to have to express high level directives that affect whether my code will be debuggable or not using multiple build settings.

At least, because I am not an animal, this will also only ever need to be done once, with an edit to the pertinent “.xcconfig” file:

// We only specify an optimization setting for Debug builds, we rely upon
// Apple's default settings to produce reasonable choices for Release builds

Now if you’ll excuse me I’m going to take a tour of other Swift-specific compiler settings to make sure I’m not shooting myself in the foot in some other way!

Test With Swift

I have recently passed a sort of tipping point where I’m indulging more and more in Swift for new code that I add to my projects. There are some instances where I will still create a new class in Objective C, primarily where I anticipate the need for dynamic runtime hijinx that might be more complicated in Swift. In general though, I’m opting for Swift. Finally.

There are many reasons to remain gun-shy about Swift, and I don’t fault anybody too much for choosing to continue forestalling the transition. I’ve spoken with many people who are as tentative as I was or moreso. Some of our collective reasons for waiting may sound familiar to you:

Swift …

  • … is not mature.
  • … requires adding bloated libraries to the app.
  • … presents an impedance mismatch with existing Cocoa design patterns.
  • … is still too risky for production code.

I don’t agree with all of these rationale, especially now that I’ve decided to dive in myself. However, they make a good basis for the argument I’d like you to consider: you should write all new unit tests in Swift.

For many of us who spent years developing a vast collection of Objective-C based classes, it does seem daunting to transition to a new language. But unit tests are different from “regular code” in a number of ways that make them a suitable place to start delving into Swift:

Unit tests …

  • Don’t ship to customers.
  • Can be as bloated as you like.
  • Test the exposed interfaces of classes more than the internal design.
  • Are not technically production code.

I’m sure somebody will argue that tests are so vital to the development process, that they are the last place one should invest in risky technology. I guess what I’m urging you to believe is that Swift is no longer risky technology. It’s not longer coming, it’s here. We will serve ourselves well to adopt it as quickly as practical. And those of us who are daunted by the challenge incorporating it into our existing, Objective-C heavy source bases, have a perfect opportunity in unit testing to get our feet wet while establishing a Swift source base that will live on well into the future. After all, your unit tests should, in theory, outlive any specific implementations of your shipping code.

The Seven Stages of Swift

For all except the newest members of our Apple development community, the arrival of Swift is something that has to be reconciled against our previous and ongoing relationship with Objective-C. This handy reference will help to guide you through this journey. Where do fall in the spectrum? How you will advance to the final stage?

Shock and Disbelief

Apple announced a new programming language? They didn’t. They couldn’t. This is not WWDC. That’s not Tim Cook. The world is upside down! Why is John Siracusa smiling?


Swift is not even a real programming language. I mean, it’s not replacing Objective-C. I mean, It’s not meant for real Cocoa programmers. I mean, it’s just Apple trying to satisfy those … weird programmers who like buzzwords! Objective-C is here to stay.


Oh crap, Swift is replacing Objective-C! Arrrrrrrggghhh! Why, Apple!? WTF? Where’s Objective-C 3.0? You’re killing Objective-C?! I love Objective-C. Die in a garbage collected fire!!!


I suppose Swift might be useful someday. Support for dynamic message dispatch is a start. If Apple gives me just one more Objective-C feature, I’ll give it a shot.


Ugh. I should really start learning about Swift one of these days! What is wrong with me?


Who cares? I could learn Swift, but what’s the point? My Objective-C skills are useless. Dot notation won. I feel this inexplicable weight in my arms. Static types are hanging from my arms. I can’t move my arms. Our apps are all going to die someday.

Acceptance and Hope

Holy crap, Swift made this so easy! Maybe I like Swift? I mean, I still love Objective-C, but I don’t love love it. Maybe we needed a new language. Maybe we were aching for a new language. Maybe we needed more buzzwords.

I like buzzwords.

(Why is John Siracusa smiling?)