The following text is transcribed from our Kotlin Multiplatform webinar. There is a video at the bottom of the blog post if you would rather listen to the segment. If you find this segment interesting, you can register for the full webinar recording and slides here. 

Slide 1

This diagram. Here’s where we find out what Native really means, and, even simplified, there’s a lot going on here.

Definitions

This input category is how the app developer writes the app. A Native Language isa language officially supported by the platform. Swift and Objc on iOS, Kotlin and Java on Android, HTML/CSS/Javascript on Web. An Other Language is a language like JavaScript on mobile, or ClojureScript on the Web. It also includes WYSIWYG visual programming interfaces that some no-code multiplatform solutions use.

The Process category is what the build chain does to the input in order to create an output. I mentioned Cross-Compilation and Trans-Compilation earlier.

But to clarify both of these, cross-compilation here is when a high level language is compiled directly to the native code for each various platforms before outputting the final product. This is called Ahead of Time compilation or AOT for short.

Trans-compilation here is when a a high level language is compiled to a another high level language which can then be fed back as input to another process, usually to a language native to the platform that can then go through the native build-chain.

Runtime here includes things external to the platform that implements portions of an execution model needed to execute the app like virtual machines, interpreters, and necessary libraries.

The Outputs category determines the type of app generated. Native Code is the low level code executed natively by the platform. Native code generates Native apps. A Native Container bridges web technologies with platform specific technologies by running web code in a webview on the native platform. A native container plus web views generates Hybrid apps. As mentioned before, a Native Language needs to be processed again to become a mobile app. But, it could also create a Web app if the output language is JavaScript or Wasm.

Once I put this together, I searched through documentation looking for how different tools worked and fit them into this model. I’m going to talk specifically about Ionic because it is a Hybrid solution, but more importantly, I’ll talk about React Native, Xamarin, and Flutter because they are so popular and, of course, I’ll talk about Kotlin Multiplatform because that’s why we’re all here. One last thing before we move on. Notice how this starts to explain some of the negative feelings we have about cross-platform solutions. For any solution, If we need to code in a new language, it will slow developers down. And, If there is an interpreter or VM between code being asked to run and code being executed, it’s going to slow the app down. And for hybrid solutions, a webview is fairly heavyweight and will slow things down even more

Slide 2

Ionic is a popular Hybrid app development tool built on Apache Cordova. You write your app in standard web technologies; the runtime includes widget libraries and native platform interop libraries, then, everything is wrapped in a native container and you get a hybrid app. Now, the web and mobile are different. On mobile you need to handle things like the offline experience, the application lifecycle and back button expectations. Hybrid solutions promise to make things easy, but you actually need to work really hard to make a hybrid app meet native expectations. 

Slide 3

React Native takes something that worked really well on web (that is, react) and makes it work on mobile better than hybrid apps. You develop mainly in Javascript and the runtime provides native or native-like widgets along with tighter interop with the underlying platform. Native code is output at runtime by the JavaScriptCore interpreter which allows the app to be categorized as Native. The differences between web and mobile are still issues to consider, and it’s easier to meet native expectations with React native, but it’s still difficult. For example, one of the problems mentioned by both Airbnb and Udacity is the 3 platform issue: to make their React Native apps more native, they had to deal with the javascript bridge and code independently for Android and iOS. This was more of a pinpoint than expected and they needed to do it more often than expected

Slide 4

Xamarin was one of the first to focus on sharing business logic with native code across platforms. It was quite a bit later in Xamarin’s life that they introduced Xamarin.Forms to share UI as well. You write your code in C#, and it gets processed to include the .NET runtimes. On iOS, it is all compiled ahead of time because iOS doesn’t allow 3rd party execution engines on Android. The Mono VM is included in the distribution so it can just-in-time compile native code at runtime. AOT is generally faster than JIT and benchmarks do show Xamarin.Android is significantly slower than Xamarin.iOS

Slide 5

The Flutter solution is yet more native because it AOT compiles on both Android and iOS. You write your app in the Dart language and, for dev builds, the Dart VM will JIT compile, but for production builds it will AOT compile all the necessary run-time libraries for widget rendering and business logic directly to native code. 

Slide 6

Kotlin Multiplatform is the most native solution yet. It is first-class for developing Android apps. Kotlin is already the best for this and fully supported by Google. Flutter is not first-class for developing Android apps until Google puts a lot more money into it and commits to it because they will need to sustain both the Material Widget library on Flutter and the standard Android widget library. Neither Xamarin nor ReactNative will ever be first-class for developing Android apps. It AOT compiles on iOS to a standard Objective-C framework which is already first-class on iOS and, even though Swift is becoming more popular, Objective-C frameworks are still prevelant. ReactNative is difficult to use in existing apps. Xamarin is impossible to use with natively developed apps. Flutter is working on it.

And that’s a huge difference: Kotlin Multiplatform is about optionally and easily sharing code. ReactNative, Xamarin, and Flutter are foreign ecosystem with a disconcerting amount of vendor lock-in. Kotlin Native also outputs to JavaScript or Wasm for sharing code with web. It’s more difficult than it should be to share React for web and ReactNative, but there is a way. Xamarin isn’t officially supporting web output yet, but people are trying. This model is quite good and this is how most people approach the definition of native, even if they haven’t thought about it as deeply as this. Often it is simplified to just the final App Types, with Web being on one end of a spectrum, Native being on the other, and hybrid filling out the in between. 

Recording: Webinar Segment

The video is from our Kotlin Multiplatform webinar. If you find this segment interesting, you can register for the full webinar recording and slides here. 

Cross-Platform Baggage

Cross-platform development is not held in high regard these days, largely because the apps that purport to provide cross-platform support have never really done the job effectively. But I believe the time has come for us to reconsider.

The arguments in favor of cross-platform development are the same as they’ve always been (D.R.Y., Risk Mitigation and Feature Parity)

Don’t. Repeat. Yourself (D.R.Y.)

There’s the argument for gaining efficiencies and cost savings through streamlining the development process. Program once to create cohesive code that can be deployed simultaneously to iOS and Android.

Risk Mitigation

There’s also the argument for minimizing risk regarding how UI will be developed. The biggest risk is that the UI won’t meet user expectations on either platform. This is a major reason why development teams opt for programming apps independently from one another. At the same time, business logic and backend development are at higher exposure because both determine how all features within an app will work. Ideally, in a cross-platform development scenario, an organization could take the time to focus on the nuances of backend and logic development, while putting less strain on UI development.

Feature Parity

The other argument is for feature parity and inclusivity, that is, fewer differences in functionality, whether iOS or Android. The benefit – you treat all users equally because they are using essentially the same program, whichever platform they choose.

Native Multiplatform Development

However, what was missing from “cross-platform” is native multiplatform development: Native CPU, Native UX, and Native developer experience and tools for iOS and Android. Cross-platform programming has the potential to thrive if the focus shifts to native coding, which is a more direct approach to produce the same functionality across platforms and devices. To better understand this, here’s a quick look at the most popular cross-platforms solutions and their native limitations.

Xamarin

Xamarin was one of the first to focus on a native approach to programming across iOS, Android, and Windows, starting with shared business logic and working its way toward shared UI with Xamarin Forms. However, its native elements are limited because it lives within its own ecosystem and uses C# (a language not native to iOS or Android development) and Microsoft Visual Studio instead of Android Studio or Xcode.

React Native

React Native (RN) represented a leap forward in terms of how developers thought about cross-platform because it empowered them to apply their web development knowledge to build native iOS and Android apps. But, like Xamarin, it too, lives within its own ecosystem, using Javascript and non-standard editors . And like Xamarin, it needs to wrap native controls and view hierarchy from its own interop, making it necessary to construct the UI with its own language.

Flutter

Flutter, a newer addition to cross-platform programming, uses its language Dart to create iOS and Android apps. Flutter also makes use of rich widgets to provide remarkable native experiences on Android and iOS platform – but the widgets are not native. Flutter also employs a shared UI platform that only works on mobile with a language (Dart) that isn’t widely used.

These are just a few examples of why cross-platform programming has traditionally been a serious challenge to manage. It’s one of the reasons I believe we should move away from the term “cross-platform.”  A more apt term is “multiplatform”, because the goal is that any code you share maximizes what each platform offers.

Kotlin Multiplatform

That brings us to Kotlin Multiplatform. It is the rising star in the multiplatform space, and is, in fact, more native than Xamarin, RN or Flutter. Currently the dominant Android language, Kotlin has a strong, enthusiastic base of developers worldwide, and is praised by the community for providing a superior developer experience. Kotlin Multiplatform enables developers to write once, and test once, then use the same code across iOS, Android, and Web apps.

While not the first multiplatform tool to split business logic and UI (for instance, Xamarin for logic/libraries and Xamarin Forms for UI), it’s more native than Xamarin, RN, and Flutter because it uses shared logic and libraries below the UI layer, which developers can interact with in the native developer environments — Xcode, Swift, and Objective-C for iOS; Android Studio and Kotlin for Android; JavaScript for the web — and it outputs native code for each platforms.

As a language, Kotlin enables developers to produce applications more cohesively. It’s a modern language that dovetails with native platforms on Android, iOS, Java, and the web, allowing development teams to build on what’s already been coded. And because it’s essentially an extension of Java, it’s relatively easy for Java developers to get started. Kotlin isn’t too much of a departure from Swift either and at Touchlab we currently have iOS developers coding in Kotlin.

Equally important, Kotlin is a way to future-proof applications developed today. It’s a sound technology investment because the code works on all platforms without vendor lock-in like Xamarin or React Native. So, whether the dominant platform in the future is web or mobile doesn’t really matter, because the code ports to either environment.

At the same time, development teams no longer have to be siloed, and instead can work together as a cohesive whole. There is no longer a need to have dedicated iOS and Android teams.  This unified mobile approach simply makes more sense operationally, technically, culturally, and financially.

Is Kotlin the safest bet? Everything indicates that it, in fact, is. In a world where we’re always looking for greater efficiencies in development time and costs, Kotlin has proven itself to be a very viable player – one that has already shown itself to be a truly multiplatform programming option.