O U R S P O N S O R S

March 12th, 2024

Kotlin Multiplatform: Building Production-Ready Applications with Confidence

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Porting Google's Java Logging Framework to Kotlin Multiplatform

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Sponsors

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Housekeeping

http://kotlin.wien

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-XenableGarbageCollection

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News

• Find us on LinkedIn�

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Community Interview

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1 Volunteer

7 easy Questions

Your favourite topic

In German or English

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Community Interview

Who are you in one sentence?

How long have you been working with Kotlin?

What are you working on (in Kotlin)?

How is Kotlin used in this project?

Tell us about a Kotlin win.

Tell us about a Kotlin fail.

Any problems/wins using Java Libraries?

Kotlin Frameworks / Features:

• Arrow
• AtomicFu
• Coroutines
• Exposed
• Gradle DSL
• HTML DSL
• Kodein
• KotlinX-IO
• Kotlin Serialization
• Ktor
• Ktorm
• MockK
• TornadoFx

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Upcoming Schedule 2024

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April: Java Vienna: "Deep dive into Hibernate� ORM 6.4 features" + TBA 8th April

April: Kotlin Vienna: Meet up @ Sentry.io 23rd April

May: Java Vienna Meetup - Venkat Edition! 6th May

May: KotlinConf 2024 Global Watchparty 23rd May� with Kotlin Vienna

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Contact us

If you have any questions or want to get in touch with us, you are more than welcome to do so!

Our contact information:

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meetup@kotlin.wien

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Welcome @ Meister

Kotlin Vienna

Meister

Tools that Work for You

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MindMeister

It all starts with an idea.

MeisterTask

Your Team. Aligned.

MeisterNote

Write Here. Write Now.

Tech

Write Here. Write Now.

KMP: Building Production-Ready Application with Confidence

Agenda

Introduction

KMP overview

KMP at Meister

Tips & Tools

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Introduction

Arcadii Rubailo

• from Moldova 🇲🇩, moved to Vienna in 2021
• 6+ years in Android development
• at Meister for 3+ years
• worked on MindMeister Android
• working on MeisterTask Android/KMP

Kotlin Multiplatform overview

Refresh KMP knowledge

KMP quiz

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A simple way to stress people

• Random questions about KMP
• Past, present and future
• Kahoot! -> Competitive
• Prizes!

KMP at Meister

A new technology for a new product

MeisterTask Notes

Your Projects Need Documentation

• Collaborative documentation for teams
• Launched in 2021
• No mobile applications until recent
• Suboptimal mobile browser experience

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Notes to Mobile

It is alive live!

What is shared

Native vs common

How it is shared

Artifacts distribution flow

Tips & Tools

Boost your confidence

Testing!

Why is it especially important for KMP?

• No manual QA process
• No native client to check on
• TDD process
• Run ./gradlew allTests

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Testing!

Kover

• Monitor test coverage
• Kotlin/kotlinx-kover
• Only JVM target for now
• Works with Kotlin-specific features
• Run ./gradlew koverVerify

Testing!

Platform-specific tests

• Checking Koin modules in src/androidInstrumentedTest

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• Verifying Build config in src/iosTest

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API validation

Monitor changes to your public API

• Check native sees API
• Avoid unintentional API changes
• How much is exposed to native
• kotlin { explicitApi() }
• public → internal
• @HiddenFromObjC

API validation

Monitor changes to your public API

• Kotlin/binary-compatibility-validator
• Dumps public Kotlin API via ./gradlew apiDump
• Checks for changes via ./gradlew apiCheck

API validation

Monitor changes to your public API

• DevSrSouza/kmp-swift-reveal
• Creates a Swift representation of Objective-C header
• Uses Source Kitten under the hood
• Doesn’t validate against previous API version

Publishing

What? Where? How?

• KMMBridge helps with XCFramework distribution
• mavenPublishArtifacts()
• manualVersions()
• spm()

Publishing

What? Where? How?

Publishing

Maven vs Package.swift

• A problem with -SNAPSHOT versions
• SPM needs a direct url to the file
• Maven resolves it via metadata
• Solution: force resolution of KMP XCFramework artifacts via a detached Gradle configuration
• https://github.com/touchlab/KMMBridge/issues/217

Swift golden hammer

SKIE - Swift Kotlin Interface Enhancer

Q&A

Any Questions?

Giancarlo Buenaflor (Gino)

Porting Google’s Java Logging Framework to Kotlin Multiplatform

(New Grad) Software Engineer @ Sentry

• Flutter & Kotlin Multiplatform SDK @ Sentry
• Google Summer of Code ‘23
• KotlinConf. ‘24 Speaker
• KMP Podcast/Video with Jetbrains

Google Summer of Code 2023

20K+ Contributors

850+ Open Source Organizations

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Including Kotlin Foundation - but I need a proposal first

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Working on a Google specific project?

Just read the Kotlin slack channel :D

Proposal accepted

Google & Jetbrains engineers as mentors

Several Google teams were showing interest for this project

What is Flogger?

Main logging framework for Java/Kotlin projects within Google

Less bytecode generated

Read more here: https://google.github.io/flogger/

What’s expected

Flogger -> KFlogger

Usable with Kotlin Multiplatform for mainly iOS and JVM

Implement basic logging functionality

Keep original Java Flogger codebase

Bazel / Blaze

Why Bazel? Because Google uses it

No idea how it’s supposed to work with KMP

Let’s just use Gradle -> great! but wait… Flogger uses Bazel so I need to compile Flogger in Gradle first

Porting Blaze to Gradle

Actually straightforward if you understand it

What dependency versions are used?

expect/actual typealias

typealias: provide alternative names for existing types

Cons:

• brittle - can lead to runtime errors
• not well documented
• Kotlin / Java interop is not perfect
• seems ‘hacky’?

Pros:

• less code

kotlinx-datetime

JVM:

Common:

kotlinx-serialization

JVM:

Common:

Just ignore the errors!

KFlogger

JVM:

Common:

Caveats

• Signatures have to match 1:1
• Types used within the expected class also need to be typealiased
• Kotlin Companion objects != Java static
• Visibility modifiers
• Doesn’t work with inner classes directly
• Need to separate the inner class and typealias that
• Just ignore errors and test the api

Testing typealiases

Test for runtime errors

How to typealias Java’s Class?

Java Flogger

Using KClass directly won’t work

• It’s an interface
• does not map 1:1 with a Java Class
• access the Java Class through .java

Klass

Common

iOS

JVM

iOS implementation

• Barebones implementation since Flogger is a big library
• No reflection on Kotlin/Native

Testing with Truth / Kruth

Truth is Google’s testing framework for Java/Kotlin projects

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Kruth -> KMP version

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Only dev builds available

What about compatibility?

• binary-compatibility-validator
• As the name suggests, only binary compatibility
• Metalava
• Used in Android at Google
• Source & binary compatibility
• Has edges cases that it doesn’t cover
• KMP support is minimal
• No perfect solution exists yet

What about compatibility?

Google’s current solution: write manual tests

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KFlogger usage

Internal politics

Flogger Team is very passionate about the framework

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.. and they disliked the KFlogger project

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gave quite some pushback

Completion

Only an experimental project

Thanks!

Feel free to ask questions!

https://github.com/buenaflor/KFlogger

https://kotlinfoundation.org/news/gsoc-2023-kflogger/