2022 Year-in-review

Monday December 19, 2022

It’s the end of the year again, and we’re feeling nostalgic 😊. We’re really proud of everything we produced for 2022, so join us for a quick review of some of our favorite highlights.

We are also offering 25% off 🎁 the first year for first-time subscribers. If you’ve been on the fence on whether or not to subscribe, now is the time!


2022 was our biggest year yet:

  • 150k unique visitors to the site.

  • 45 episodes released for a total of 31 hours of video, and 15 blog posts published.

  • Over 200k video views, 6 years watching time, and over 44 terabytes of video streamed.

  • 1 new project open sourced and dozens of updates to our other libraries.

But these high-level stats don’t even scratch the surface of what we covered in 2022:

Episodes and open source

This year’s episodes were action-packed, to say the least. We made use of many new, advanced features of Swift 5.7, especially result builders, existentials, and constrained opaque types, in order to push the Swift language and SwiftUI to the limit of what they can accomplish. And along the way we released one brand new open source library, as well as many significant updates to some of our most popular libraries.


The first 17 episodes of 2022 brought 3 substantial improvements to our Parsing library:

  • A builder syntax that allows one to concisely build complex parsers. For example, before parser builders we could construct a parser of a comma-separated lists of users like so:

    let user = Int.parser()
      .take(Prefix { $0 != "," }.map(String.init))
    let users = Many(user, separator: "\n")

    While not bad, there is a lot of superfluous noise when using the take and skip operators in order to incrementally parser from the beginning of an input string. Using parser builders this becomes:

    let users = Many {
      Parse(User.init(id:name:isAdmin:)) {
        Prefix { $0 != "," }.map(String.init)
    } separator: {
  • We added error messaging for when a parser fails on some input. For example, using the above parser to parse a string in which the boolean “true” is misspelled:

    try users.parse(
      2,Blob Jr.,false
      3,Blob Sr.,tru

    …causes the following error to be thrown:

    error: unexpected input
     --> input:3:11
    3 | 3,Blob Jr,tru
      |           ^ expected "true" or "false"
  • And last, but not least, we added the ability for parsers to be “inverted” so that they can print well-structured data types back into their raw input format, such as strings. There is only one small change that needs to be made to the above users parser to magically turn it into a parser-printer:

     let users = Many {
    -  Parse(User.init(id:name:isAdmin:)) {
    +  Parse(.memberwise(User.init(id:name:isAdmin:))) {
         Prefix { $0 != "," }.map(String.init)
     } separator: {

    With that one change you can now print an array of User values back into a string:

    try users.print([
      User(id: 1, "Blob", isAdmin: true),
      User(id: 2, "Blob Jr.", isAdmin: false),
      User(id: 3, "Blob Sr.", isAdmin: true),
    2,Blob Jr.,false
    3,Blob Sr.,true

If you want to learn more about parsers, be sure to check out our collection of episodes (including the free 5-part tour), and give the library a spin today!


We devoted a 5-part series of episodes to uncovering many of Apple’s concurrency tools from the past, present, and into the future. We started by diving deep into threads and queues, which have been around on Apple’s platforms for many years. Those tools are powerful for running concurrent code, but can be difficult to wield correctly, and the compiler does nothing to help you out.

Understanding the tools of the past helps us understand why Swift’s new concurrency tools take the form they do. The new tools are meant to allow us to write concurrent code in a style that looks like “regular” code, and do so in a way that allows the compiler to catch race conditions at compile time rather than runtime.

The Composable Architecture

We had two separate series of episodes dedicated to improving nearly every facet of our popular SwiftUI architecture library: the Composable Architecture.

  • First, we more tightly integrated Swift’s new concurrency tools into the library by making it possible to use structured concurrency in your feature’s effects. This makes it much easier to construct effects, including complex, long-living ones, and makes it possible to tie the lifecycle of effects to the lifecycle of views.

    While covering these topics we also had a fun digression into Swift 5.7’s new existential type features (starts at 18:12, subscription required). It shows how one can think of existential types as a kind of “infinite” enum, which helps build intuition of why protocols seem so different from regular, concrete types.

  • Second, we revamped the fundamental unit that defines a feature in the Composable Architecture: the reducer. It changed from being a struct that wraps a function to a protocol. This allows one to create all new types for encapsulating the logic for a feature, which unlocks new ways of structuring and composing features, and even a whole new way of managing dependencies.

    While covering these topics we also had a fun digression into improving type inference in result builders (starts at 21:34, subscription required). We showed that a combination of generic result builders and buildExpression can allow types to more fully propagate to all parts of the builder, greatly enhancing its ergonomics.

  • In addition to those improvements, we also made a massive improvement to the testing facilities of the library, thanks to a collaboration with Krzysztof Zabłocki. We introduced the concept of “non-exhaustive TestStore to the library, which allows you to write high level integration tests between many features without needing to assert on everything that happens in the feature. This can make it possible to write powerful tests that are not brittle and difficult to maintain.


One of the most common forms of asynchrony is time-based asynchrony, and Swift 5.7 introduced the Clock protocol as a means of abstracting over the concept of “sleeping” in an async context. This protocol even makes it possible to write controllable, testable async code, and can even make Xcode previews more responsive for fast, iterative UI design.

Our 2-part deep dive into the Clock protocol explains why this tool is so important, and shows how to make a few new conformances, such as the “immediate clock” and “test clock”. We even open sourced a brand new library that brings these tools, and more, to everyone’s codebase.

SwiftUI navigation and modern SwiftUI

SwiftUI navigation can be complex, but it doesn’t have to be. That’s why we devoted 12 episodes to the topic where we give a precise definition of what navigation means in an application, explored SwiftUI’s navigation tools (including tabs, alerts, modal sheets, and links), and then showed how to build new navigation tools that allow us to model our domains more concisely and correctly.

This year we updated that series of episodes to include iOS 16’s new navigation tools, including NavigationStack, NavigationPath, and the new navigationDestination view modifier. After those episodes we released an update to our SwiftUI Navigation library that makes it possible to drive all forms of navigation from a single piece of enum state, with a case for each possible destination in your feature. This can massively simplify your navigation logic, and prevent a large class of bugs from ever appearing in your code.

Once all of those tools were under our belt we started a brand new series of episodes (still ongoing at the time of publishing this article) covering best, modern SwiftUI practices. We do this by rebuilding one of Apple’s most interesting demo applications, “Scrumdinger”. This application shows off many navigation flows, interesting user interactions, and some complex effects such as timers, persistence, and even a speech recognizer.

Blog posts

We wrote 15 blog posts this year, but there were 3 main standouts.

Xcode has a wonderful feature that can notify you of subtle problems in your code by showing a prominent, yet unobtrusive, purple warning on the problematic line of code. This happens if Xcode detects a threading problem in your code, if you mutate UI code on a non-main thread, and more.

These warnings are incredibly useful, but sadly Apple does not make it possible to create them from 3rd party libraries…well, at least not without some trickery. In our blog post, “Unobtrusive runtime warnings for libraries”, we show how to create these warnings, allowing library maintainers to notify users when certain invariants are broken.

iOS 16 brought a whole new suite of navigation APIs for dealing with stack-based navigation. One of those tools, NavigationPath, seemed like complete magic when inspected closely. It allows you to drive navigation from a type-erased collection of Hashable data, and interestingly it allows you to encode the path to raw data and decode the data back into a type-erased collection.

This somehow works even though all of the type information of the elements has been erased. We make use of hidden, but public, Swift functions _mangledTypeName and _typeByName as well as Swift 5.7’s new existential type features in order to reverse engineer how NavigationPath works.

Testing is by far the #1 priority of the Composable Architecture. The library provides a tool, the TestStore, that makes it possible to exhaustively prove how your features evolve over time. This not only includes how state changes with every user action, but also how effects are executed, and how data is fed back into the system.

The testing tools in the library haven’t changed much in the two and a half years since release, but thanks to close collaboration with Krzysztof Zabłocki and support from his employer, The Browser Company, the Composable Architecture was updated to bring first class support for “non-exhaustive” test stores.

Read our article, “Non-exhaustive testing in the Composable Architecture”, for an overview of the “why” and “how” of exhaustive testing, as well as when it breaks down, and how non-exhaustive testing can help.

See you in 2023! 🥳

We’re thankful to all of our subscribers for supporting us and helping us create this content and these libraries. We could not do it without you!

Next year we have even more planned, including powerful new navigation tools in the Composable Architecture, deep dives into existential types and other powerful type system concepts, and we plan exploring new forms of content (live streams!).

To celebrate the end of the year we are also offering 25% off the first year for first-time subscribers. If you’ve been on the fence on whether or not to subscribe, now is the time!

See you in 2023!

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