Touchlab attended KotlinConf 2019 in Copenhagen, Denmark. As anticipated, the conference was a milestone event for the development of Kotlin Multiplatform and its community of practitioners and contributors.

VIDEOS! There will most likely be ‘official’ videos published soon, but the content is already up in the live stream so we organized links to each talk for you.

This post also contains reactions to Kotlin Multiplatform sessions attended by Touchlab’s Ben Whitley (multiplatform mobile engineer with iOS background) and Kevin Galligan (Partner). 

Before we jump in, we’d like to call out two important moments from the conference:  

1. During his keynote, Kotlin Lead Language Designer Andrey Breslav highlighted Touchlab as a critical community member to JetBrains’ mission to usher in a new era of mobile development with Kotlin Multiplatform (view clip).

2. During the closing Q&A panel an audience member asked about approaches for getting iOS developers onboard for a KMP pilot. JetBrains’ VP of Developer Advocacy Hadi Hariri recommended organizations speak to Touchlab as we’re actively working with clients on this exact topic (view clip).

Opening Keynote by Andrey Breslav (view keynote)

Pre conference take

The KotlinConf keynote is must watch for anybody that’s interested in Kotlin. Any major new stuff will be announced.

Ben’s reaction

•  Think of Kotlin as an entire ecosystem, not just a language. 
• The goal is to make Kotlin the default language for starting any project and make it a universal solution for every platform. For any and all levels of experience, platforms, scales, and application.
• Dropped the term “full-stack Kotlin” which I personally hadn’t heard before.
• No major new features in Kotlin 1.4. Focus is on quality and performance, which is smart, given the current build times. 

Kevin’s reaction

• They are very focused on making Multiplatform a reality. 
• You’ll be able to run/debug native iOS apps from Android Studio. That will be a huge adoption driver.  
• 1.4 will bring a lot of stability and performance/compiler improvements, which will be a big deal.

Sharing Is Caring – Kotlin Multiplatform for Android Developers by Britt Barak (view talk + slides) 

Pre conference take

This will be a good intro talk. It includes not only native, but JS and backend code.

Ben’s reaction

• Getting started (aka project configuration and setup) is currently the biggest pain point. Something we can probably all agree on. 
• Big plurality of different needs, and therefore different architectures. This is still an open ended issue for KMP, and one we’re very familiar with at Touchlab. Because there’s many different use cases and it’s still open ended, this wasn’t intended as a talk on KMP architecture.
• https://github.com/aakira/kotlin-multiplatform-libraries is a very cool resource to find packages
• Overall a really good getting started talk, even though a lot of it was very familiar for us at Touchlab.
• I’d strongly recommend checking out the video of it for Android developers interested in KMP. 

• Future goal is a complete KMP ecosystem
• A lot of the talk was a history of KMP through Kotlin versions up until this point
• Included a shoutout to Touchlab

Kevin’s reaction

• For the future they’re going to focus on docs and onboarding much more, as well as for specific use cases like native mobile. The team had been much more focused on “general” multiplatform.
• The original discussion of “multiplatform” started in 2016, which is around when Kotlin JVM was 1.0. JS has been around and in use significantly longer than native.

Coroutines! Gotta catch ‘em all! by Florina Muntenescu and Manuel Vivo (view talk)

Pre conference take

Concurrency for native will be mostly centered around coroutines, so an intro to coroutines is valuable.

Kotlin Multiplatform in Action: more than 10 projects for iOS and Android with Shared code by Alexandr Pogrebnyak (view talk)

Pre conference take

IceRock has been shipping KMP for a while, and has published templates and libraries to help. This will probably be a useful talk for practical KMP advice.

Kevin’s reaction

• Have released a set of libraries targeted at native mobile development that we should review for use on projects
• They have a shared UI library for native mobile. Uses native widgets to render. That’s a lot of work to build but assuming we can mix with fully native screens, this is something we’ll be taking a look at.

Bridge the physical world: Kotlin/Native on Raspberry PI by Qian Jin (view talk)

Pre conference take

More Kotlin Native. It’s being deployed to an IOT device, which may be interesting to see.

Your multiplatform Kaptain has arrived by Ahmed El-Helw (view talk)

Pre conference take

Careem is shipping KMP in a major platform. This is critical info for orgs getting serious about KMP. We’ll be there for sure.

Ben’s reaction

• Very early users of KMP
• KMP exciting and nerve-wracking for management
• Communication processes were a solution to problems between iOS and Android teams
• This is a very good “lessons learned” type of talk
• Shoutout to Touchlab generics patch and Kevin’s blog post about generics 
• Mentioned basically everything Kevin has put out there at this point, including CrashKiOS and Xcode Plugin. 
• Ended with a cool/funny poem (last pic)

Shipping a Mobile Multiplatform Project on iOS & Android by Ben Asher and Alec Strong (view talk)

Pre conference take

More KMP-in-production experts. We work directly with the Square team doing this, and chat often with Ben, so we’re very much looking forward to see what they have to say.

Ben’s reaction

• High initial setup cost for KMP, will be worth the effort
• Features develop parity even if they start out the same (or similar). Good point, not discussed enough
• Shout-out to Kevin’s concurrency talk. They recommend doing the suspend and lambda methodology (which is what we do pretty regularly).
• Pros and cons of monorepo, which is under discussed good con for iOS devs: they often don’t even have JVM.
• Didn’t mention Touchlab CrashKiOS, which is exactly what they need for the improved crash reporting they want. 

Kevin’s reaction

• Square and PlanGrid are some of the earliest shipping apps, and have really had to figure out a bunch of the stuff.
• I’ve been involved directly with Square, and have worked a fair bit with Ben because they ship on Windows, so we’ve been publishing our libraries to Windows.
• Great thoughts for introducing your team to and educating your team on KMP.
• Pick something that the teams don’t like and/or that’s fairly critical and needs to run the same. Sync for PlanGrid and transaction search for Cash.
• Stopped taking notes because my talk was happening after theirs

Kotlin Native Concurrency Explained by Kevin Galligan 
(view talk + slides)

Links included in Kevin’s talk

• https://github.com/Autodesk/coroutineworker
• https://github.com/Badoo/reaktive
• https://medium.com/@kpgalligan/kotlin-native-stranger-threads-ep-1-1ccccdfe0c99
• https://github.com/Kotlin/kotlinx.coroutines/blob/native-mt/kotlin-native-sharing.md
•  https://github.com/kpgalligan/MTCoroutines
• https://github.com/touchlab/DroidconKotlin (look for the kpg/mt_coroutines branch)

Pre conference take

If you want to do KMP on native, you need to understand concurrency. This is our talk, and a must see, obviously

Kevin Interviewed at KotlinConf (view interview)

I Walk The Line: What Parts Of An App Should be in Kotlin Native – and What Parts Shouldn’t? by Ellen Shapiro (view talk)

Pre conference take

Ellen knows mobile tech, and brings a lot of iOS experience to the KMP equation. We’re definitely checking this talk out.

Ben’s reaction

• Developer enthusiasm is key to adoption of cross platform products
• Gave away copies of Ray Wenderlich Kotlin book to people who ask interesting questions – good idea for engagement
• Ellen came up with MVSP (Model ViewState Presenter) architecture to replace MVP. It’s a form of unidirectional data flow partially inspired by SwiftUI
• Shoutout to Kevin’s talk yesterday, she said “it goes into a ton of detail” 

• Know why you’re using Kotlin Multiplatform, that will dictate how much and what KMP you should do

Going Native: How I Used Kotlin Native to Port 6 Years of Android Games to iOS in 6 Months by Ana Redmond (view talk)

Pre conference take

Ana got into native early on and has done very interesting work. This will be a really good talk.

Ben’s reaction

• Ana is a perfect example of what Kevin (and Ellen in her talk) says: if you’re going to do cross platform or common code, know why you’re doing it. 
• She’s using KMP for shared UIs; very difficult and impressive. As she says, this is possible because of few external dependencies (basically none), which is why this is a good use case for shared UI.
• She wrote her own KMP WeakRef wrapper to avoid retain cycles in iOS, pretty smart and cool. Has its limitations, won’t catch retain cycles across KMP and native code. 
• Lessons learned
  • Classes > Objects: to avoid the threading and mutability issues that Kevin’s always talking about
  • Lists > Arrays: this is vindicating as I’ve found this myself and I’ve been saying it for a while now
  • Initialization order: she found very weird behavior in overriding initializers in KMP. See corresponding pic. Something we’ll be looking into at Touchlab. 

Effective Kotlin-Swift Interoperability by John Rodriguez (view talk)

Pre conference take

Kotlin/Swift communication is a huge topic for KMP. Improving the situation for iOS developers will be critical for adoption, so this is a critical topic to understand.

Kevin’s reaction

• Went very deep on interop details. I learned some new things, especially WRT enums.

Kotlin/Native: Answers Your Won’t Find on the Internet 
by Eugenio Marletti (view talk)

Pre conference take

Eugenio is a member of the JetBrains developer relations team, focused on KMP and native. He’s going to be critical to improving the documentation and onboarding experience, so you should definitely check this talk out.

Touchlab will be attending KotlinConf 2019 in Copenhagen, Denmark. We anticipate the conference to be a milestone event for the development of Kotlin Multiplatform and its community of practitioners and contributors.

If you’re in town, please let us know because we’d love to meet with you.

If you’re unable to attend the conference, no worries. We’re hosting a Kotlin Multiplatform Fireside Chat in New York City for engineering managers. We’ll discuss and review all the KMP updates from the 2019 conference. Register here.

The following is a list of KMP talks we’ll be attending. If you’d like to be notified when the live stream for these sessions is available, register on the KotlinConf website.

Opening Keynote by Andrey Breslav  

Time: 9:00 – 10:00

Our take: The KotlinConf keynote is must watch for anybody that’s interested in Kotlin. Any major new stuff will be announced.

Sharing Is Caring – Kotlin Multiplatform for Android Developers by Britt Barak

Time: 10:15 – 11:00

Our take: This will be a good intro talk. It includes not only native, but JS and backend code.

MPP in 1.3.X and beyond by Dmitry Savvinov and Liliia Abdulina

Time: 11:15 – 12:00

Our take: Another KMP intro, from JetBrains engineers

Coroutines! Gotta catch ‘em all! by Florina Muntenescu and Manuel Vivo

Time: 11:15 – 12:00

Our take: Concurrency for native will be mostly centered around coroutines, so an intro to coroutines is valuable.

Kotlin Multiplatform in Action: more than 10 projects for iOS and Android with Shared code by Alexandr Pogrebnyak

Time: 14:00 – 14:45

Our take: IceRock has been shipping KMP for a while, and has published templates and libraries to help. This will probably be a useful talk for practical KMP advice.

BRIDGE THE PHYSICAL WORLD: KOTLIN/NATIVE ON RASPBERRY PI by Qian Jin

Time: 14:00 – 14:45

Our take: More Kotlin Native. It’s being deployed to an IOT device, which may be interesting to see.

YOUR MULTIPLATFORM KAPTAIN HAS ARRIVED by Ahmed El-Helw

Time: 15:15 – 16:00

Our take: Careem is shipping KMP in a major platform. This is critical info for orgs getting serious about KMP. We’ll be there for sure.

Shipping a Mobile Multiplatform Project on iOS & Android by Ben Asher and Alec Strong

Time: 16:15 – 17:00

Our take: More KMP-in-production experts. We work directly with the Square team doing this, and chat often with Ben, so we’re very much looking forward to see what they have to say.

PREPARING YOUR KOTLIN MULTIPLATFORM DEVELOPMENT ENVIRONMENT by Big Nerd Ranch

Time: 16:15 – 17:00

Our take: Another KMP intro. Good to get multiple perspectives.

KOTLIN NATIVE CONCURRENCY EXPLAINED by Kevin Galligan

Time: 17:15 – 18:00

Our take: If you want to do KMP on native, you need to understand concurrency. This is our talk, and a must see, obviously 🙂

I Walk The Line: What Parts Of An App Should be in Kotlin Native – and What Parts Shouldn’t? by Ellen Shapiro 

Time: 10:15 – 11:00 

Our take: Ellen knows mobile tech, and brings a lot of iOS experience to the KMP equation. We’re definitely checking this talk out.

GOING NATIVE: HOW I USED KOTLIN NATIVE TO PORT 6 YEARS OF ANDROID GAME CODE TO IOS IN 6 MONTHS by Ana Redmond

Time: 14:00 – 14:45

Our take: Ana got into native early on and has done very interesting work. This will be a really good talk.

Effective Kotlin-Swift Interoperability by John Rodriguez

Time: 16:15 – 17:00

Our take: Kotlin/Swift communication is a huge topic for KMP. Improving the situation for iOS developers will be critical for adoption, so this is a critical topic to understand.

KOTLIN/NATIVE: ANSWERS YOU WON’T FIND ON THE INTERNET by Eugenio Marletti

Time: 16:15 – 17:00

Our take: Eugenio is a member of the JetBrains developer relations team, focused on KMP and native. If you go to KotlinConf for KMP and skip this talk, I’m not even sure why you’re going.

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Kotlin Multiplatform tutorial

Can I use Kotlin Multiplatform for an existing app? 

What Kotlin Multiplatform libraries is Touchlab using today? 

How much of my code are we going to be able to share with KMP? 

How much weight does KMP add to our apps?  

We use Swift. How’s the interop with KMP?   

Kevin: It currently presents to Swift/Objc as an Objc library. The usual Swift Objc interop issues will apply, but the generated header takes advantage of many of the naming you can insert for Swift. You can also now have ge- nerics (I highlight that because we did that, too). With ABI stability, direct Swift interop will be more of a priority. Possibly early next year, but there is no timeline yet from the team.

What type of ecosystem and tool are available? 

Justin: The existing, mature, and exciting ecosystems of native Android and iOS development are available. Not everything can be pulled into shared code, but the beauty of sharing business logic is that most of it can be shared. A mature and loved library that is already in Kotlin is very close to joining the KMP ecosystem. For example, once SqlDelight was set up to output Kotlin, it didn’t take long to make it compatible with shared code…and iOS developers love that they don’t need to deal with CoreData anymore but they can keep all the other stuff they love.

How will KMP affect our ability to recruit and onboard new iOS devs? 

Justin: Equal or better. Some iOS devs will be happy to spend time on getting the UI and platform-specific stu right. Some iOS devs want to become mobile devs and will be happy to start learning Kotlin. All iOS devs will be happy to know that it doesn’t force them out of the ecosystem and lose their identity.

Sam: Kotlin Native will be much better received by new iOS developers than many other code sharing schemes. The ability to code UI natively while treating the common code as a normal framework is much less foreign than tools which require them to learn an all new framework.

How fast is the compilation time? 

Kevin: Not super fast, but the general dev process is to code on the JVM side first, which is more optimized, then rebuild the Xcode framework and call it from iOS. The next major version of Kotlin should be focused on various performance improvements (compilation being one of them).

Thoughts on handling concurrent operations in Kotlin Multiplatform? 

Kevin: Kotlin Native’s concurrency model is different than the “classical” mod- els of the JVM and Swift/Objective C. It is something that new developers, coming from either Android or iOS backgrounds, will need to understand. It can be confusing at first, but the goal of these changes is less error- prone concurrency. There are some early libraries to assist with concurrency, but later this year we expect multithreaded coroutines to emerge for Native. At that point, most concurrency will be managed by libraries (like most concurrency is managed now). You’ll need to understand how it works, but the libraries will handle the heavy lifting for you.

How do I encourage optimal code sharing from the beginning? 

Justin: Focus on well-established architecture principles of keeping the UI layer thin and modularizing code. Something new may be separating Android-specific libraries from common code but this is often a small amount because business logic is, by its nature, less platform-specific.

What’s the value-add over other technologies? 

Justin: Kotlin is THE language for Android. KMP doesn’t significantly change the way you develop native Android apps. KMP interop is native so there is very little run-time overhead and less boiler-plate code while developing. KMP outputs a standard iOS framework so iOS devs are still in familiar territory. By its nature, it keeps up with platform-specific technologies that motivate and excite strong native developers and those looking to join the space (retention and hiring). It doesn’t create its own ecosystem so it’s not a ‘B’ big decision, easy to iterate and revert, very little up-front cost compared to others.

Sam: It’s optional, meaning you can do some, and no big decisions. Natively integrated: the interop is platform native, which is unlike pretty much all other options. Open source. Code sharing, so you can write and test your critical logic and architecture, but don’t build a dissatisfying UI. The language is popular and modern. That is important for libraries, hiring, and productivity.

Does KMP work with Android WearOS, Apple WatchKit, TVOS?

Kevin: Kotlin 1.3.60 will add support for WatchKit and TvOS. Anything on the Android side already uses Kotlin, so there are no compatibility issues (Kotlin is the preferred language for Android).

How mature and stable is KMP?

Kevin: The language and tooling have gone through significant change over the past couple years, but the build tools and features of the ecosystem have stabilized. The tooling and support libraries will continue to mature rap- idly during the remainder of 2019 and into 2020. As for stability, there is no “multiplatform” at runtime. It is a build time construct. Kotlin JVM is super stable. Kotlin Native’s runtime is stable, although you will occasion- ally run into things you don’t expect. Usually a result of cryptic messaging. That will also improve over the next year. Major apps are releasing Kotlin Native into production now.

What’s the best way to set up the dev experience for iOS devs?

Kevin: I think it’s important to establish that the plan is not to start writing everything in Kotlin. The shared code will support the native development experience of Swift and Xcode, especially as SwiftUI takes over UI development on iOS. Introduce Kotlin as a modern language that shares much of the syntax and concepts of Swift, and at an architectural level, it’s important to start thinking of our teams as “mobile developers” rather than specifically Android and iOS. Having an Xcode plugin for Kotlin means iOS developers can start reading and debugging Kotlin in the shared code without needing to dive in with new languages and tools. Once that knowledge is learned, the iOS team can start pushing code that the Android (and possibly web) teams will use. It’s important to minimize the idea that the iOS teams will just be getting code from the Android app, although that is often the initial reaction, as Kotlin is an ‘Android thing’.

How do you start migrated a codebase to KMP?

Kevin: Pick one part that needs to happen on both platforms, ideally something that the iOS team isn’t excited about. SQLite is a good option, if you’re us- ing it. Nobody likes Coredata. SqlDelight is a far better option. From there, possibly networking, analytics, or any logic intensive operations that need solid testing. Because it’s “optional” sharing and natively integrated, it’s easy to weave shared code into existing code.

Can I hire for Kotlin Multiplatform? 

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Kotlin Multiplatform tutorial