turing complete with a stack of 0xdeadbeef

Writing by tag

Quickly switching between Xcodes

I try to have only one Xcode installed at a time for simplicity and tidiness. But such a setup is rare as we often must manage stable releases and beta versions simultaneously.

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Implementing Dark Mode and using CGColor

For an iOS project that I am currently working on, I am implementing Dark Mode. The codebase is approaching 7 years old, it is mostly Swift with some legacy Objective-C, and it currently supports iOS 11 and above. Aside from the tedium of ensuring the updated colors are being used throughout the codebase, I expected this task to be straight-forward. However, there were some unanticipated issues.

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Mac app tests fail with hardened runtime enabled

I recently discovered that unit tests and UI tests for a macOS Xcode project will fail with obscure error messages if the hardened runtime is enabled. It took me awhile to realize what the actual source of the problem was, because the error messages led me in the wrong direction. Hopefully this will save you some time.

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Selecting an Xcode version on GitHub Actions CI

I have started using GitHub Actions for CI on a new project as a replacement for my usual setup on Travis CI. It generally seems to be much faster and more reliable so far. It also has an equivalent feature set, as far as I can tell. But one issue that I have run into is selecting a specific Xcode version, which is a bit cumbersome and not fully documented.

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Debugging a subtle Swift bug that will make you facepalm

The other day I was debugging a crash in a UI test for an open pull request at work. The bug turned out to be extremely subtle and difficult to notice. I spent way too much time staring at the changes, trying to understand what was wrong. Let’s see if you can spot the error.

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How to run sysdiagnose on iOS

And on all the Apple things

When you file a radar for a bug on one of Apple’s platforms, you should (usually) always attach a sysdiagnose. A sysdiagnose provides a lot of helpful information for the person who is trying to understand how the bug happened. Amongst other things, it contains logs from various parts of the OS, and all recent crash logs. Without it, the person on the other end of your report inside Apple may not be of much help. On macOS running sysdiagnose is somewhat common, but what about iOS?

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Measuring Swift compile times in Xcode 9

Using -Xfrontend Swift compiler flags

The Swift type-checker remains a performance bottleneck for compile times, though it has improved tremendously over the past two years. You could even say the type-checker has gone from being drunk to sober. To help users debug these issues, awhile back Jordan Rose added a frontend Swift compiler flag that would emit warnings in Xcode for functions that took too long to compile, or rather took too long to type-check. In Xcode 9, there’s a new, similar flag for checking expressions.

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Testing and mocking without OCMock

For Swift and Objective-C

OCMock is a powerful mock object unit testing library for Objective-C. Even if you are using Swift, as long as your classes inherit from NSObject, you can use some of its features. But what if you are writing pure Swift code which does not have access to the dynamic Objective-C runtime? Or, what if you don’t want your Swift code to be hampered by NSObject subclasses and @objc annotations? Perhaps, you merely want to avoid dependencies and use ‘plain old’ XCTest with Objective-C. It’s relatively easy and lightweight to achieve the same effect in some testing scenarios without using OCMock.

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Migrating to Swift 3

Advice, tips, and warnings

I spent most of my free time last weekend and a few days of last week on migrating my Swift code to Swift 3.0 — I migrated my open source projects as well as my private side projects. Overall, I would say my experience was “OK”. It definitely could have been better, but I think the largest problem was overcoming the cognitive hurdle of seeing all the changes and errors from Xcode’s migration tool at once. The best thing to do is wipe away the tears, put your headphones on, and start hacking. 🤓

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Building type-safe, composable data sources in Swift

A modern approach to collection views and table views

In iOS development, the core of nearly every app rests on the foundations provided by UICollectionView and UITableView. These APIs make it simple to build interfaces that display the data in our app, and allow us to easily interact with those data. Because they are so frequently used, it makes sense to optimize and refine how we use them — to reduce the boilerplate involved in setting them up, to make them testable, and more. With Swift, we have new ways with which we can approach these APIs and reimagine how we use them to build apps.

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Better Core Data models in Swift

How Swift can bring clarity and safety to your managed objects

As I continue my work with Core Data and Swift, I have been trying to find ways to make Core Data better. Among my goals are clarity and safety, specifically regarding types. Luckily, we can harness Swift’s optionals, enums, and other features to make managed objects more robust and more clear. But even with the improvements that Swift brings, there are still some drawbacks and limitations with Xcode’s current toolset.

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Swift, Core Data, and unit testing

Working around Swift's constraints to unit test models

Core Data is probably loved as much as it is shunned by iOS developers. It is a framework of great power that often comes with great frustration. But it remains a popular tool among developers despite its pitfalls — likely because Apple continues to invest in it and encourages its adoption, as well as the availability of the many open-source libraries that make Core Data easier to use. Consider unit testing, and Core Data gets a bit more cumbersome. Luckily, there are established techniques to facilitate testing your models. Add Swift to this equation, and the learning curve gets slightly steeper.

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Adaptive user interfaces

Exploring iOS size classes and trait collections

When the App Store launched, there was one iPhone with one screen size and one pixel density. Designing your user interfaces was relatively simple and the technical debt of hard-coding them was cheap. Today, developers and designers face many challenges in creating apps that must work on dozens of different devices. Long gone are the days of 480x320. We can no longer depend on physical screen sizes and must always be prepared for the next generation of devices.

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Apples to apples, Part III

A modest proposal: can Swift outperform plain C?

When I find my code is slow or troubled, friends and colleagues comfort me. Speaking words of wisdom, write in C. It is understood that foregoing the features and abstractions of high-level programming languages in favor of their low-level counterparts can yield faster, more efficient code. If you abandon your favorite runtime, forget about garbage collection, eschew dynamic typing, and leave message passing behind; then you will be left with scalar operations, manual memory management, and raw pointers. However, the closer we get to the hardware, the further we get from readability, safety, and maintainability.

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On the value of benchmarks

A brief examination of measuring code performance

As Apples to apples, Part II made its way around the web, it was praised as well as critiqued. The latter largely consisted of questions regarding the real-world applications of these benchmarks. In general, benchmarks should be taken with a grain of salt. I want to take a minute to clarify my thoughts on benchmarks and how I think they can be valuable.

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Apples to apples, Part II

An analysis of sorts between Objective-C and Swift

If at first you don’t succeed, try, try again. Practice makes perfect. These proverbs have encouraged us all in many different contexts. But in software development, they tug at our heartstrings uniquely. Programmers persevere through countless nights of fixing bugs. Companies march vigilantly toward an MVP. But after 1.0 there is no finish line, there is no bottom of the 9th inning. There are more bugs to be fixed. There are new releases ahead. The march continues, because software is not a product, it is a process.

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Apples to apples

A comparison of sorts between Objective-C and Swift

When Craig Federighi arrived at his presentation slide about Objective-C during this year’s WWDC keynote everyone in the room seemed puzzled, curious, and maybe even a bit uneasy. What was happening? As he continued, he considered what Objective-C would be like without the C, and the room abruptly filled with rumblings and whispers [1] as developers in the audience confided in those around them. If you had been following the discussions in our community about the state of Objective-C (and why we need to replace it) during the previous months, you could only have imagined one thing: Objective-C was no more — at least not as we knew it.

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