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Multiplatform Fractals with Kotlin

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Eugene Petrenko

eugene.petrenko@jetbrains.com

@jonnyzzz

JetBrains, @jonnyzzz,KTUG Munchen 2018

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@jonnyzzz

JetBrains, Kotlin user, phd, developer advocacy

Blogger https://jonnyzzz.com

Kotlin, Java, Go, C/C++, Qt, Toolbox App

Server-side, Desktop, DSLs, fun!

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https://en.wikipedia.org/wiki/Mandelbrot_set#/media/File:Mandel_zoom_00_mandelbrot_set.jpg

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Languages Hell

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Multiplatform Kotlin

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Why Multiplatform

Share common code� Business logic, Utilities, UI-core, DTO, …

Use platform for else� UI, API, Frameworks

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JS in JVM�JVM in JS�Native in JS

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Kotlin common code

actual / expect

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Fractals App

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JS/JVM/Native Fractals

JS application to try in browser

JVM web server to render fractals

Console application for text-mode fans

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The Application

common: Render fractal for a given area

jvm: ktor web app

js: render in browser (fast) and fetch

native: console fractals

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Fractals

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https://en.wikipedia.org/wiki/Mandelbrot_set#/media/File:Mandel_zoom_00_mandelbrot_set.jpg

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https://commons.wikimedia.org/wiki/File:Mandel_zoom_04_seehorse_tail.jpg

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https://en.wikipedia.org/wiki/Mandelbrot_set#/media/File:Mandelbrot_set_image.png

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Complex Numbers?

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Complex Numbers

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Mandelbrot Set

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M = Mandelbrot set

https://en.wikipedia.org/wiki/Mandelbrot_set

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https://en.wikipedia.org/wiki/Mandelbrot_set#/media/File:Mandel_zoom_00_mandelbrot_set.jpg

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Pixel Color

Depends how fast Zn leaves the 2-area

HSL color space (not RGB)

Magic formula from Wikipedia

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Color = HSL( Zn, 60, 80 )

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Pixel Color Library

We have no kotlin-common library

expect / actual

a library for JS and JVM

a stub implementation for Native Console App

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actual / expected

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expect (common)

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actual (JVM)

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HSL in Kotlin/Native

We render to console, monochrome

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Demo Time!

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Standard Libraries

Kotlin-stdlib� Collections & sequences & functional API� Higher order functions (with, apply, etc)� Exceptions

kotlin.test�infrastructure libraries (e.g. kotlinx.html)

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Tests

Multiplatform kotlin.test library

Check your code is OK for every platform

Write once debug everywhere!

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Gradle plugins

kotlin-platform-common => common

kotlin-platform-jvm => JVM / Android

kotlin-platform-js => JavaSctipt

konan => Native

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expectedBy dependency in Gradle

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JavaScript with Kotlin

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JavaScript in Kotlin

module.js

common� *.kt

Kotlin/JS

*.kt

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JavaScript: kotlin-frontend-plugin

app.js

Webpack

module.js

npm deps

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Useful for JavaScript

gradle kotlin-frontend-plugin

npm create-react-kotlin-app

library kotlin-wrappers� react, css, styled-components, etc.

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Useful for Full Stack

GitHub kotlin-fullstack-sample� js, jvm

KotlinConf App� js, jvm, iOS, Android

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KotlinConf App

Common code

Kotlin-JS code

Kotlin-JVM code

Kotlin/Native

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Useful Links

kotlinlang.org

try.kotlinlang.org and Kotlin Koans

Slack: slack.kotl.in or kotlinlang.slack.com

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Q & A

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Ask me @jonnyzzz

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Trick: Different Libraries?

Use expect for API

Use actual to glue

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Logging framework? Networking? JSON? �Android?

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Summary

Common code, expect/actual

Code reuse between platforms

Kotlin/Native, Kotlin/JS, Kotlin/JVM

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NO TRESPASSING

beyond this slide

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RGB vs HSL

Common code - on implementation!

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HSL in JavaScript

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HSL in Java

Same as in JavaScript

Call a copy-pasted Java snippet

No need to convert code to make it work

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kotlinlang.org

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Apache 2.0 / GitHub

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Build Applications For

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Why Kotlin?

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Releases & Commits

<sometime> 2010

<started>

15 February 2016

Kotlin 1.0

28 November 2017

Kotlin 1.2

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Coding Time!

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Useful Links

kotlinlang.org

try.kotlinlang.org and Kotlin Koans

Slack: slack.kotl.in or kotlinlang.slack.com

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DSLs in Kotlin

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DSL

A domain-specific language (DSL) is a computer language specialized to a particular application domain. This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains...

(from Wikipedia)

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Specific DSLs

SQL / Regexp

State machines

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Custom Stack�JetBrains MPS can help!

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Embedded DSLs

Uses existing language

Java-style builders

Fluent APIs

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Your current stack

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Fluent API. C#

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DSLs = Domain Specific ...

Kotlin Syntax 💖 DSLs

Static typed

IDE support, Code Completion, ...

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easy to read/write/express/share

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DSL Coding Time!

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kotlinx.html�library�on GitHub

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Docs

Extension Functions�kotlinlang.org/.../extensions.html

Lambdas�kotlinlang.org/.../lambdas.html

Type-Safe builders�kotlinlang.org/.../type-safe-builders.html

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Coroutines

Minimalistic compiler part� suspend keyword

Libraries to provide� fun: async/await, actors, � channels, yield returns, …

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generators / yield return

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kotlinx.coroutines �library�on GitHub

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Multiplatform

Common modules� platform independent

Reuse Kotlin code between platforms� expect / actual keywords

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App in Kotlin� Server-side

Android / iOS� Web

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https://github.com/jetbrains/kotlinconf-app

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Kotlin Usage Highlights

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At JetBrains

40+ people in Kotlin Team

Used in most JetBrains Products

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Q & A

kotlinlang.org

try.kotlinlang.org and Kotlin Koans

Slack: slack.kotl.in or kotlinlang.slack.com

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Videos / Slides�

kotlinconf.com

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kotlin.xml.bind

github.com/jonnyzzz/kotlin.xml.bind

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coroutine: launch & delay

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Story: TeamCity.Node

Support for NodeJS related build runners for TeamCity

Released on 14 January 2013

github.com/jonnyzzz/TeamCity.Node

jonnyzzz.com/blog/2013/01/14/kotlin-nodejs-and-teamcity/

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What else is possible?

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What I did with Kotlin?

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Committer in Spek

A Specification Framework

github.com/JetBrains/spek

jonnyzzz.com/blog/2013/03/26/bdd-test-framework-with-kotlin

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kotlin.xml.dsl

github.com/jonnyzzz/kotlin.xml.dsl

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kotlin.xml.bind

github.com/jonnyzzz/kotlin.xml.bind

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Story: Config DSLs

A XML configuration files editor via Kotlin DSL

jonnyzzz/TeamCity2DSL

jonnyzzz/Log4j2DSL

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Java Server Side

Internal project. Java 1.8, SpringFramework, GRPC, Gradle, HTTP, Jetty

Use from January 2016

New code 99% Kotlin code: � 698 Java vs 404 Kotlin files

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Building Kotlin

CMD, Ant

Gradle, Maven

Kobalt

Webpack

IntelliJ IDEA, Android Studio

...

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Back in 2010: Why Kotlin?

A better language for JetBrains

plus experience in tooling & languages support

C#, Scala, Groovy, JavaScript, C/C++, …

Static, Concise, Effective, Toolable, Interoperable, Pragmatic

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Multi Platform Kotlin

JVM

Android (Dalvik)

JavaScript

Native (LLVM), preview

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Kotlin in 42 minutes

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Show me the code!

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100% Java Interop

We have 17+ years codebase in Java

No way to re-write it

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.kt and .java files are OK in one module/project

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100% Android Friendly

Java bytecode version is 1.6

All language features �(and lambdas) are available

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Official on Android

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Kotlin for JavaScript

Static typed web programming

Reuse code between platforms

Webpack, React, Gradle support

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Kotlin / Native

Preview, Work in Progress

No VM & fast

LLVM� macOS, iOS� Linux, r. Pi

Soon:Windows

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