Sebastian Sellmair
@Sellmair
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Kotlin | IntelliJ | Fleet | Multiplatform @JetBrains // #Kotlin | #Gradle | #Android // Opinions are my own.
München, Bayern
Joined January 2014
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After 3 years of blood, sweat and tears:
Kotlin Multiplatform is finally stable 🎉
I never thought that it will take us so much time to pull this off. Let me explain what we did 🧵
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After more than two years of working hard on Kotlin Multiplatform, I am very proud to pick up new responsibilities as Technical Lead 🙏😇
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Just merged a Kotlin Compiler Frontend performance optimization for Kotlin 1.6.20 that I am pretty proud of 😇
Analyzing a file in okio/commonMain took:
Before ~48s
After ~1s
Note: This still has to go through the whole release/QA process. Let's hope for the best 🤞🤞
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🐘 Gradle is hard! I invited my team again to teach about the fundamentals. In this session, we re-implemented the Kotlin Gradle Plugin from scratch 👻
We talked about:
- buildSrc
- writing Gradle Plugins
- invoking the Kotlin Compiler
- executing code
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🐨 Android Studio Koala landed in IntelliJ master 🐨
- 989K changes
- 9K commits
- 1K merge conflicts
- 5K failing tests initially
- 2TB of maven artifacts shipped
This was one crazy journey. I hope it is alright. Will be writing a blog post with my learnings from it soon 👻
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📢 Gradle is *not* slow 📣
Here is one of the most effective ways to optimise your IntelliJ <- Gradle sync times 🧵
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🐘 Almost all engineers, working with large/complex builds will struggle eventually. Kotlin uses Gradle. Since I know a thing or two about Gradle, I invited my team and gave an introduction to the absolute basics:
Tasks and Configurations:
Recording 📽️
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Grade Configuration Cache support for Kotlin Multiplatform is merged. Expected in Kotlin 1.9.0 🎉
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I think I won at procrastination.
I wanted to build iOS apps.
Instead of learning Swift and Xcode, I joined JetBrains and spent 4 years fixing Kotlin Multiplatform.
Now I finally got what I wanted. 😌
#InnerPeace
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Pretty Proud 🥹
62 commit refactoring went into Kotlin Gradle Plugin master today. Replaced three complex class hierarchies around KotlinCompilation with one simpler hierarchy.
This can be used as the foundation for fixing long-standing Multiplatform/Android issues.
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Merging Android Studio Koala back into IntelliJ:
Started with 5000 failing tests today; Made it to 1400 remaining ☝️
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🧙 Wizards are no replacement for education or documentation
The suffering is real, which is the reason for which I created this extensive KMP (+Compose) setup guide
🪜Step by Step
📺 Companion 'In Action' recordings
De-Wizarding Kotlin Multiplatform:
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📣 Kotlin Multiplatform Users online meeting, next Monday, 20.06, 17:00-18:00 CET
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Insider Tip:
Some projects rely on lightweight code generation. This is often annoying since it requires running the code generation before symbols can resolve within the IDE. You can use the 'prepareKotlinIdeaImport' task to automatically run tasks during Gradle sync! 👍
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Yesterday was the day. We released 1.9.20 and declared multiplatform stable. There are still many things we would like to improve and continue working on and we're very dedicated to this. Thanks to everybody involved and special thanks to all early adopters 😍
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Android Studio Koala🐨 2024.1.2 (Feature Drop) landed in IntelliJ master 🎉
The new process is working.
The entire merge took 3-4 days and we're close to Android Studio's master.
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Today's release of IntelliJ 2024.2 Beta supports (up to) Android Studio Koala 🐨 Feature Drop
(Android Gradle Plugin versions up to 8.6.0-canary07)
This is the first time IntelliJ has ever supported even Canary Android tooling and I am proud of that.
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Taking over, merging Android Studio Koala 🐨 back into IntelliJ master. We increased man-power for maintaining the Android Plugin in IntelliJ.
@TheTechW0lf
and me are working on a new process to keep IntelliJ and AS in close sync.
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Next Kotlin Multiplatform Community Meeting is scheduled for Monday, February 06 · 18:00 CEST 🙌
Topics:
➡️ Kotlin Target Hierarchy DSL (preview)
➡️ New Multiplatform Gradle Sync
➡️ Multiplatform Composite Build support
➡️ ...
Join:
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Kotlin Multiplatform Tip:
Unless you being 💯% sure what you're doing:
NEVER. USE. expect class, object, interface...
ALWAYS. USE: expect fun!
If you need platform specifics:
Use expect fun for factory functions
```
expect fun MyInterface(): MyInterface
```
Have you encountered the problem of not having FileSystem.SYSTEM in Okio available from common sources before?
Time to bump to 3.9.0, where it's now available from common sources (with JVM/native targets supported) - contributed by
@Sellmair
and myself.
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I always felt that the 'run button' in IntelliJ was working a little bit unreliable in Gradle projects. This was especially apparent for
#multiplatform
projects.
Upcoming in Kotlin 1.9 and IDEA 23.2: A new implementation that aims for 100% reliability
Implementation Details: 🧵
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Kotlin Multiplatform Gradle Tip:
Try
import_orphan_source_sets=false
in your
This will prevent the IDE from importing useless source sets like `androidTestRelease` etc.
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IntelliJ/Gradle protip:
When your Gradle sync/import into IDE fails with no useful error message:
Try just executing `./gradlew` without arguments in the command line. This will often provide you with useful information what went wrong during the configuration phase 👻🐘
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🐘 Gradle Intro 3: The Kotlin Gradle Plugin Model (TCS)
Recording of me trying to explain Kotlins
T: Targets
C: Compilations
S: Source Sets
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#Multiplatform
Tip:
In most cases, interface + factory function is much more convenient and suitable than "expect class".
Matter of fact: I am getting convinced that "expect class" is only suitable for the cinterop and commonizer tools.
#kmp
#kmm
#kotlin
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Almost every time I got very frustrated working within a certain codebase, I struggled with abstract classes.
Over time I developed a very easy-to-follow recipe on how to refactor from 'inheritance' to 'composition' 😌
Wrote this article with examples!
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Started working on Multiplatform Gradle Import (Sync) performance recently
()
Pretty proud 😇:
Preliminary Results of optimizations:
-40% warm Gradle Import (Sync) times for compared to Kotlin 1.7.10
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Just compiled my first Kotlin Multiplatform Toy project with K2. The future is here! 🙌😍
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A simple change like:
Was able to reduce initial dependency download times from 9 minutes to 3 minutes on my machine ⚡️
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Kotlin Multiplatform PSA:
Unfortunately, our Intellij <- Chipmunk merge has several issues with Multiplatform and Android (as Chipmunk also had). We're working on resolving this.
Will post when this is resolved. Until then 2022.2 might not be your EAP of choice for KMP 😢
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Compose for web got me heavily excited 💕. Here is why:
Disclaimer ** I am employed by JetBrains, working on Kotlin Multiplatform support. Opinions are still my own 🤷♂️ **
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🐨 Trying to land Android Studio Koala in IntelliJ master. This is insane. I start the CI and once its green, new merge conflicts appeared 😫 We're working on new approaches to tame this process.
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🐘 Introduction to 'Gradle fundamentals: Tasks & Configurations'.
Recording 📹:
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Little proud 😇
It seems like I just merged a fix for a nasty issue I reported before working at JetBrains. 2 years ago! 🎉
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⚠️ When setting up Kotlin/Multiplatform:
Avoid setting 'dependsOn' edges as much as possible!!! Those are low-level compiler concepts that should have never been exposed to users in the buildscript. So far almost any buildscript I see gets those wrong 🥲
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🐘Applied Gradle: One Test, Multiple Implementations
Sharing an advanced technique, previously used to ensure a K2 re-implementation matches it's K1 counterpart
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Who still believes in "Insanity is doing the same thing over and over and expecting different results", clearly has not worked with a large projects CI 🥸🥲
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Back in 2019, while still working at
@QuickBirdEng
(still one of the best companies to really learn software engineering), I got excited about Kotlin/Multiplatform, tried it and wrote the following blogpost:
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Please, dear library authors 🙏
Put the maven coordinates to your library at the most visible spot in your README. This is the *one* thing I wanna know 90% of the time when opening it: What's the coordinates! TELL ME!
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Started merging back Android Studio🐨 Feature Drop back into IntelliJ...
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Naive me. It took me way more time that I would like to admit to finally understand that IDE analysis and CLI compilation have vastly different goals and complexities. JetBrains IDEs work so well, that you fail to see the magic under the hood. We just take it for granted.
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I feared the Web for too long. A little time ago I tried Kotlin/JS and I absolutely enjoyed coding with it. Yesterday, I built my first hobby project web app using compose. I absolutely LOVED it ❤️ This is so much fun! I really feel at home 💕
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Wrote my first Kotlin/Native CLI tool with Okio.
@jessewilson
I love it, thank you so much! 😍
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Productivity tip:
Create one Kotlin/IntelliJ project called 'scripts' or 'tools'.
Create one file per script, containing a "main" function.
Enjoy just pressing the 'run' button in IntelliJ to launch your scripts 🥳
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📣 Kotlin Multiplatform Users online meeting, today 17:00-18:00 CET/Munich.
Feel free to share your experience, issues or wishes for the future.
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Looking up to people like
@abreslav
and
@relizarov
, I also told him how happy I was at
@QuickBirdEng
, but I dropped the statement: 'JetBrains would be the only company that I would consider leaving
@QuickBirdEng
for'. He invited me to visit the JetBrains office.
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📣 Kotlin Multiplatform Users online meeting, next Monday, September 12 · 6:00 – 7:00pm CEST
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Wanting to be productive is like wanting to be cool.
If you're trying to hard, it does not work 🤷♂️
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PSA for Multiplatform/Android Library Authors:
Android Gradle Plugin version 7.1.0-alpha13+ will require Kotlin 1.6.10+ for proper support of Gradle publications.
Further Details:
Support ticket:
Discussion:
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This was a huge effort. One of our engineers, Anton, worked on it for quite some time and had to touch many internal components. All of them just got better imho.
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A few months later, I was hired for the Kotlin-Ide team in JetBrains, soon after
@DSavvinov
founded a new team within JetBrains called 'Kotlin Multiplatform Core' which was special as it was a 'feature team' caring about all things Multiplatform. Our goal: Multiplatform Stable!
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Kotlin Multiplatform is all about interoperability: Being native on all targets. Android? Yes, Kotlin is *the* language for Android and the same toolchain is used. There is nothing special about it. iOS? We directly compile using LLVM, we can directly call Foundation APIs
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Spontaneously joined a Twitter Space with
@Louis_CAD
and it was great fun😊
We were talking about Android, YouTrack, Open Source, Kotlin and of course Kotlin Multiplatform. We will definitely repeat this 😇
Sorry for the app crashing several times on my end though 👀
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I thought: How hard can it be to make the IDE 'less red'. I thought, this will be quick: Just tell the IDE the same things that we tell the CLI compiler: Two weeks and multiplatform will work out. 🫠
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Hackathon
@QuickBirdEng
! Result: Proof of concept of a multiplatform OpenCV wrapper 🥳
The image below calculated and plotted the histogram of
@JulianLenz_
's post with pure Kotlin code. It runs natively on macOS and Android! 😎
#opencv
#mpp
#multiplatform
#kotlinmultiplatform
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Kotlin Multiplatform Tip:
Do not create dependsOn edges from *Test to *Main
e.g. `nativeTest.dependsOn(nativeMain)`. This is very likely not what you want! The visibility from *test to *main sources will be done automatically (by associated compilations not by matching names).
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The review took me the whole last week. It was roughly 60 commits im the end.
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However, how can code be shared across several targets? Sharing code across Android and iOS? Sharing code across all Apple targets? A new library format and 'Kotlin Metadata Klib' was invented (metadata containing signatures/'headers', but no bodies of functions).
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IntelliJ 2024.2 Beta is likely shipping Android Studia Koala, Feature Drop 🐨
The gap between IntelliJ and Android Studio is closing.
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Tried Kotlin for the first time directly after watching this in 2017. This literally changed my life.
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In any case: Building 'hierarchical multiplatform' took us two years. What have we spent on the third year? The answer is quite simple: We stabilised. We built APIs for Google to provide better Android support, we figured out what works well and what we need to deprecated.
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We worked hard to allow for direct interoperability, while also allowing the IDE to analyse shared sources. We called this 'hierarchical multiplatform (hmpp)' and resolving dependencies for the IDE in this mode is really 👀 non-trivial! Have a look:
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Almost a month ago, I tweeted an "IntelliJ/Gradle protip" that advised to execute `./gradlew` when IntelliJ does not show useful error messages after failed import.
As promised: Here is a follow-up 🧵 on why this happens in IntelliJ and how to fix it 👀😬
IntelliJ/Gradle protip:
When your Gradle sync/import into IDE fails with no useful error message:
Try just executing `./gradlew` without arguments in the command line. This will often provide you with useful information what went wrong during the configuration phase 👻🐘
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I regret starting this tweet with 'Gradle is hard!'. I actually think that it is fun, first and foremost. As a community, we need to stop fearing our tools, but rather learn them, understanding what makes them great.
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This is very interesting and has some very counterintuitive implications when it comes to 'types' when working with the commonizer:
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Refactoring classical state machines with
@kotlin
coroutines can be extremely rewarding.
This went from 546 to 181 lines of code.
#kotlin
#coroutines
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Looking forward to Kotlin 1.3.70 and the first 1.4 EAP 🎉🥳
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Maintaining Android for IntelliJ and Fleet just recently got moved into my Team, called 'Kotlin in Fleet'. This can be described as a SWAT team, which picks up topics that do not have clear ownership but are important for building Kotlin Multiplatform Tooling.
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All conflicts resolved; Manual Smoke Testing is OK. Let's start the battle with CI.
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I am so proud being part of this team since over one year now 🥳❤️
Happy Birthday, Kotlin 🎂
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I am convinced that building good products requires 'knowing your competition well'. Since I am working on Kotlin, IntelliJ & Fleet, I thought well...
Let's call my friend
@JulianLenz_
and learn about 'What makes Flutter great' 🙇♂️
That was fun🥰
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Android Studio | IntelliJ Tip
The Android IDE plugin seems to request a full Gradle re-sync, if the IDE gets opened. You might want to try the `android.gradle.project.startup.activity.disabled` registry key (set it to true) to disable this behaviour 👀
Use is at your own risk 🤷♂️
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One really complex issue we had to solve is providing tooling for native sources that use platform libraries. Those native headers did not define intersections APIs for platforms (like sharing code between macosX64 and iosX64). We built a tool called 'commonizer'.
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e.g.
fun foo(a: _size_t) (e.g. macosX64)
fun foo(a: size_t) (e.g. iosX64)
where _size_t = size_t = kotlin.Long (macos)
where size_t = (ios)
The commonizer is clever enough to figure out that there shall be a function
fun foo(a: size_t) as result.
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Combining Kotlin Multiplatform + Flutter = pretty interesting stack!! 👀
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Kotlin Multiplatform Tip:
Creating intermediate source sets will still require dependsOn edges to 'commonMain' and 'commonTest'. Your platform compilation might still work, because those will also declare this dependency, but the IDE and metadata compilation will require this.
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@mobiledev_pro
Thanks for trying the alpha version. Feedback is always welcome and valuable. Glad to hear you like it as multiple teams at JetBrains and Google are working hard on this free tool 😊
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Having an
#androiddev
project with many, many modules containing instrumented Android tests that you want to execute all at once ( `./gradlew connectedAndroidTest ` )?
Keep them from interfering and enforce serial execution with this trick 🤪👻
#android
#kotlin
#gradle
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So in the end: Newer IDEs and newer Kotlin Gradle Plugins will just collaborate and the IDE will pass the mainClass (which shall be executed) down to the Gradle task. Execution happens entirely inside Gradle and therefore shall be 100% correct and reliable. Feedback very welcome
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We were a little faster than anticipated: most fixes already made it to 2022.2 beta1 (available now). Please try it and feel free to provide feedback 💪
Kotlin Multiplatform PSA:
Unfortunately, our Intellij <- Chipmunk merge has several issues with Multiplatform and Android (as Chipmunk also had). We're working on resolving this.
Will post when this is resolved. Until then 2022.2 might not be your EAP of choice for KMP 😢
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Hackathon at
@QuickBirdEng
🔥!
Developing
@kotlin
multiplatform OpenCV.
@JulianLenz_
and I just drew the first pixels from pure Kotlin code (Running natively on MacOS) 🥳🎉😱
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I am using this DSL for testing Kotlin MPP source set hierarchies! Kind of like it, however, the unary minus is easy to forget/overlook 🤨
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PSA: Entities in Kotlin prefixed with `.*Kpm` are not part of the public API. We will hopefully be able to mark them properly as internal soon.
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The commonizer's job is to get fed platform libraries (klibs) and figure out the APIs that can be called when sharing code across them. However, klibs on different platforms tend to use different typealiases on different platforms. They might also be aliasing to different types
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The next step is to provide a clear boundary between Android and other plugins in IntelliJ ensuring the usage APIs are stable for our products. We are aware of many issues in the Android plugin. Whilst having a limited amount of resources, I am convinced that we can be smart here
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Kotlin 1.3.71 coming in 🥳
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I created a new GitHub repository and messed up by not creating a nice 'initial commit'.
Showcasing `git commit-tree`, synthesizing a new initial commit, for fixing this 🆙
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Relevant changes:
Feel free to contact me on the public Kotlin Slack for further details/code explanation if you're interested. 🙃
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As a first step, we re-invented the process of merging Android Studio into IntelliJ, which worked: IntelliJ is pretty close to Android Studio's master branch now. We called this 'Project Bifrost'
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As promised:
Kotlin 1.3.60 is now officially released and brings a lot of improvements to
#Kotlin
#multiplatform
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Very proud, that I fixed a small issue with Kotlin Multiplatform and Realm 😊
#Kotlin
#KotlinMultiplatform
#KotlinMPP
#Realm
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