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Kotlin Multiplatform
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The Hitchhikers Guide Through
Kotlin Multiplatform
The Hitchhikers Guide Through
Kotlin Multiplatform
@cafonsomota
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speakerdeck.com/cmota/
the-hitchhikers-guide-through-kotlin-multiplatform
@cafonsomota
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No content
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a brief history of time
“In the beginning the Universe was created. This had made many people
angry and has been widely regarded as a bad move.”
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android iOS
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Dark Theme
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android iOS
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Photo by Fabian Grohs on Unsplash
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Photo by Fabian Grohs on Unsplash
a wild application idea
appears!
develop it for Android and iOS.
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-hire a team of specialised developers
-define requirements
-plan features development
-start development/ write unit tests
-write t-specs for SQA validation
-cross-checking validation between both platforms
(or jacks)
Steps
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~2xthe team
the cost
the status meetings required
the time spent on development
the time spent on testing
native
the time spent on bug fixing
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Photo by Fabian Grohs on Unsplash
a wild application idea
appears!
develop it for Android and iOS and web.
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~3xthe team
the cost
the status meetings required
the time spent on development
the time spent on testing
the time spent on bug fixing
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let’s find a solution
that works on all
platforms.
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2008 2012 2018
2013
2011 2017
2006 2010
2009 2015
* Kotlin Multiplatform
*
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- smaller team
- typically half of the cost needed on native
- small learning curve for web developers
(advantages)
Cross-platform
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- chained to the framework implementation of UI
- new updates from the OS will take time to adopt
- performance is not the same
- some native code might need to be written
- OS/ device features are dependent on the fw support
- dart is not widely used language (for now)
(disadvantages)
Cross-platform
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how can we have
the best of both
worlds?
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how can we have
the best of both
worlds?
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kotlin
“42.”
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- developed by JetBrains
- open source
- concise, safe, interoperable, tool-friendly
- supported/ used by Google for Android Development
- it’s more than “just for Android”
Kotlin
Server-side Android Kotlin JS Native
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Mutability
etc.
Null safety
Default
values
Type
inference
String
interpolation
when
Collections
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NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
NullPointerException
TransactionTooLargeException
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public class Conference {
private String mName;
private String mLocal;
private List mTechs;
public Conference(String name, String local, List techs) {
mName = name;
mLocal = local;
mTechs = techs;
}
public String getName() {
return mName;
}
public void setName(String name) {
Conference.java
(less code)
Concise
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data class Conference (val name: String,
val location: String,
val techs: List)
(less code)
Concise
Conference.kt
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Less bugs!
more free time
(and happier team… and management)
(less code)
Concise
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-getOrElse()
-find()
-filter()
-filterNot()
-filterNotNull()
-flatMap()
-mapNotNull()
-all()
-any()
-sumBy()
-zip()
-…
-take()
-takeLast()
-sortBy()
-sortByDescending()
-groupBy()
-map()
(collections)
Language features
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mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
> [1, null, 2, null, 3, 4, 5, 6, 7, 8, 9]
(collections)
Language features
output
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> [1, 2, 3, 4, 5, 6, 7, 8, 9]
(collections)
Language features
output
mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
.filterNotNull()
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> [2, 4, 6, 8]
mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
.filterNotNull()
.filter { it % 2 == 0 }
(collections)
Language features
output
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> [8, 6, 4, 2]
mutableListOf(1, null, 2, null, 3, 4, 5, 6, 7, 8, 9)
.filterNotNull()
.filter { it % 2 == 0 }
.sortedDescending()
(collections)
Language features
output
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- small learning curve involved
- easily to go from JavaScript/ Swift into Kotlin and back
(from a developers’ point of view)
Easy to learn
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var variable = 42
variable = 1
let value = 42
var variable = 42
variable = 1
val value = 42
*adapted from http://nilhcem.com/swift-is-like-kotlin/
(variables and constants)
Kotlin vs Swift
Kotlin
Swift
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fun greet(name: String, day: String): String {
return "Hello $name, today is $day."
}
greet(“Porto", “Saturday")
*updated from http://nilhcem.com/swift-is-like-kotlin/
func greet(_ name: String,_ day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet(“Porto", “Saturday")
Kotlin
Swift
(functions)
Kotlin vs Swift
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kotlin multiplatform
“‘Resistance is useless!’ How can anyone maintain a positive mental
attitude if you’re saying things like that?”
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K
otlin multiplatform
using kotlin in projects
that target more than
one platform
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(advantages)
- language features
- kotlin first!
- low risk
- you decide what’s worth to share across projects
- interoperability
- consistency across platforms
- strong community support
Kotlin Multiplatform
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first reaction
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view view view view
model
parser
network
presentation presentation presentation presentation
network network network
parser parser parser
model model model
presentation presentation presentation
desktop
web
iOS
android
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business logic business logic business logic
model
parser
network
presentation
model
parser
network
presentation
model
parser
network
presentation
model
parser
network
presentation
business logic
view view view view
desktop
web
iOS
android
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android iOS web desktop
model
parser
network
presentation
common
view view view view
java/kotlin objective-c/ swift (kotlin) JS supported in jvm
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but how can they expect to communicate?
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declared at common module
expect
declared at android module
actual
declared at iOS module
declared at …
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we want a platform-specific value for name
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expect object Platform {
val name: String
}
commonMain
src/commonMain/sample/Platform.kt
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commonMain
src/commonMain/sample/Platform.kt
- define actual on android
- define actual on iOS
targets: android and iOS
expect object Platform {
val name: String
}
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src/iOSMain/sample/Platform.kt
actual object Platform {
actual val name: String = "Android"
}
actual object Platform {
actual val name: String = "iOS"
}
src/androidMain/sample/Platform.kt
platform-dependent code
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IntelliJ will ask you declare the implementations for actual
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*.kt
common
expect
JVM
actual
*.kt, *.java, *.jar
Native
actual
*.kt, *C, Swift, Framework
JS
actual
*.kt, *.js, NPM
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medium.com/@cafonsomota
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demo
"For a moment, nothing happened. Then, after a second or so, nothing
continued to happen.”
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github.com/cmota/commit19
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- implement UI
- RecyclerView (Android)/ UITableViewController (iOS)
- make network request
- parse response object
- notify the UI
- that there’s new content available to be draw
- reload the list
project structure
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android iOS
Retrofit Alamofire
GSON/ Moshi JSONSerialization
MVP, MVVM, MVI MVVM, ELM
RxJava RxSwift
Tests Tests
Activity UIViewController
RecyclerView UITableView
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Retrofit Alamofire
GSON/ Moshi JSONSerialization
MVP, MVVM, MVI MVVM, ELM
RxJava RxSwift
Tests Tests
Activity UIViewController
RecyclerView UITableView
android iOS
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Retrofit Alamofire
GSON/ Moshi JSONSerialization
MVP, MVVM, MVI MVVM, ELM
RxJava RxSwift
Tests Tests
android iOS
Activity UIViewController
RecyclerView UITableView
unnecessary duplication
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class CommitAPI(engine: HttpClientEngine) {
private val client = HttpClient(engine) {
install(JsonFeature) {
serializer = KotlinxSerializer()
}
}
suspend fun fetchSpeakers(): AllSpeakersEntity {
val response = client.get{ url ("$URL")}
val json = response.readText()
return Json.parse(SpeakersEntity.serializer(), json)
}
}
network
src/commonMain/data/CommitAPI.kt
android
business logic
model
parser
network
presentation
view
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class CommitAPI(engine: HttpClientEngine) {
private val client = HttpClient(engine) {
install(JsonFeature) {
serializer = KotlinxSerializer()
}
}
suspend fun fetchSpeakers(): AllSpeakersEntity {
val response = client.get{ url ("$URL")}
val json = response.readText()
return Json.parse(SpeakersEntity.serializer(), json)
}
}
parser
src/commonMain/data/CommitAPI.kt
android
business logic
model
parser
network
presentation
view
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{
“speaker": "Carlos Mota",
"company": "WIT SOFTWARE",
"title": "Lead Software Engineer",
"bio": “... GDG Coimbra organizer and Kotlin evangelist, he also has
a huge passion for travel, photography, space and the occasional run.",
"talk_title": "The Hitchhikers Guide Through Kotlin Multiplatform",
“talk_description”:”... But what I told that you could just develop
in Kotlin and run it seamlessly on all devices? Here comes Kotlin
Multiplatform!",
"talk_time":"16:00",
"img": “https://commitporto.com/static/speakers/carlos.jpg"
...
}
json response
http://gist.github.com/cmota/…commit-speakers.json
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{
"speaker": "Carlos Mota",
"company": "WIT SOFTWARE",
"title": "Lead Software Engineer",
"bio": "... GDG Coimbra organizer and Kotlin evangelist, he also has
a huge passion for travel, photography, space and the occasional run.",
"talk_title": "The Hitchhikers Guide Through Kotlin Multiplatform",
"talk_description”:"... But what I told that you could just develop
in Kotlin and run it seamlessly on all devices? Here comes Kotlin
Multiplatform!",
"talk_time":"16:00",
"img": "https://commitporto.com/static/speakers/carlos.jpg"
...
}
json response
http://gist.github.com/cmota/…commit-speakers.json
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@Serializable
data class Speaker(val speaker: String,
val company: String,
val title: String,
val bio: String,
@SerialName("talk_title") val title: String,
@SerialName("talk_description") val description: String,
@SerialName("talk_time") val schedule: String,
val img: String)
model
src/commonMain/data/Speaker.kt
ktor-client-serialization
android
business logic
model
parser
network
presentation
view
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class SpeakersListPresenter(val speakers: GetSpeakers) {
lateinit var view: ISpeakersListView
fun attachView(appView: ISpeakersListView) {
view = appView
fetchSpeakersList()
}
…
presenter
src/commonMain/presentation/SpeakersListPresenter.kt
android
business logic
model
parser
network
presentation
view
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interface ISpeakerEvent {
fun onNewList(speakers: List)
fun onNewListFailed(e: Exception)
}
presenter
src/commonMain/presentation/ISpeakerEvent.kt
android
business logic
model
parser
network
presentation
view
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class SpeakersListPresenter(val speakers: GetSpeakers) {
lateinit var view: ISpeakersListView
fun attachView(appView: ISpeakersListView) {
view = appView
fetchSpeakersList()
}
…
presenter
src/commonMain/presentation/SpeakersListPresenter.kt
android
business logic
model
parser
network
presentation
view
onCreate()/ viewDidLoad()
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fun fetchSpeakersList() {
PresenterCoroutineScope(defaultDispatcher).launch {
speakers(
onSuccess = { view.onSpeakersListFetched(it) },
onFailure = { view.onSpeakersListFailed(it) })
}
}
presenter
src/commonMain/presentation/SpeakersListPresenter.kt
android
business logic
model
parser
network
presentation
view
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class GetSpeakers(val commitAPI: CommitAPI) {
suspend operator fun invoke(
onSuccess: (List) -> Unit,
onFailure: (Exception) -> Unit) {
val result = commitAPI.fetchSpeakers()
coroutineScope {
launch(uiDispatcher) {
try {
onSuccess(result.speakers)
} catch (e: Exception) {
onFailure(e)
}
…
}
domain
src/commonMain/domain/GetSpeakers.kt
android
business logic
model
parser
network
presentation
view
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No content
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class MainActivity : AppCompatActivity(), ISpeakersEvent {
val presenter by lazy { ServiceLocator.getPresenter }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
presenter.attachView(this)
}
override fun onNewList(speakers: List) {
setUiComponents(speakers)
}
...
android
src/commonAndroid/presentation/MainActivity.kt
android
business logic
model
parser
network
presentation
view
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class MainActivity : AppCompatActivity(), ISpeakersEvent {
val presenter by lazy { ServiceLocator.getPresenter }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
presenter.attachView(this)
}
override fun onNewList(speakers: List) {
setUiComponents(speakers)
}
...
android
src/commonAndroid/presentation/MainActivity.kt
android
business logic
model
parser
network
presentation
view
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object ServiceLocator {
val commitApi =
CommitAPI(PlatformServiceLocator.httpClientEngine)
val getPresenter: SpeakersListPresenter
get() = SpeakersListPresenter(GetSpeakers(commitApi))
}
expect object PlatformServiceLocator {
val httpClientEngine: HttpClientEngine
}
init
src/commonMain/ServiceLocator.kt
android
business logic
model
parser
network
presentation
view
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actual object PlatformServiceLocator {
actual val httpClientEngine: HttpClientEngine by lazy {
OkHttp.create ()
}
}
init
src/mainAndroid/PlatformServiceLocator.kt
android
business logic
model
parser
network
presentation
view
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actual object PlatformServiceLocator {
actual val httpClientEngine: HttpClientEngine by lazy {
Ios.create()
}
}
init
src/iosMain/PlatformServiceLocator.kt
iOS
business logic
model
parser
network
presentation
view
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override fun onBindViewHolder(viewHolder:
SpeakerViewHolder, position: Int) {
val speaker = speakers[position]
Glide.with(viewHolder.speakerPhoto)
.load(speaker.img)
.apply(RequestOptions.circleCropTransform())
.into(viewHolder.speakerPhoto)
viewHolder.speakerName.text = speaker.speaker
viewHolder.talkTitle.text = speaker.talkTitle
viewHolder.container.setOnClickListener {
action.onUserClickAction(speaker, it)
}
}
android
src/mainAndroid/presentation/SpeakersListAdapter.kt
android
business logic
model
parser
network
presentation
view
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override fun onBindViewHolder(viewHolder:
SpeakerViewHolder, position: Int) {
val speaker = speakers[position]
Glide.with(viewHolder.speakerPhoto)
.load(speaker.img)
.apply(RequestOptions.circleCropTransform())
.into(viewHolder.speakerPhoto)
viewHolder.speakerName.text = speaker.speaker
viewHolder.talkTitle.text = speaker.talkTitle
viewHolder.container.setOnClickListener {
action.onUserClickAction(speaker, it)
}
}
android
src/mainAndroid/presentation/SpeakersListAdapter.kt
android
business logic
model
parser
network
presentation
view
you can keep using your android libraries
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class SpeakerTableViewController:
UITableViewController, ISpeakersListView {
lazy var presenter = ServiceLocator.init().getPresenter
var speakers = [Speaker]()
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
presenter.attachView(view: self)
}
…
iOS
iosApp/iosApp/SpeakerTableViewController.swift
iOS
business logic
model
parser
network
presentation
view
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class SpeakerTableViewController:
UITableViewController, ISpeakersListView {
lazy var presenter = ServiceLocator.init().getPresenter
var speakers = [Speaker]()
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
presenter.attachView(view: self)
}
…
iOS
iosApp/iosApp/SpeakerTableViewController.swift
iOS
business logic
model
parser
network
presentation
view
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func onSpeakersListFetched(speakers: [Speaker]) {
self.speakers = speakers
self.tableView.reloadData()
}
iOS
iosApp/iosApp/SpeakerTableViewController.swift
iOS
business logic
model
parser
network
presentation
view
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override func tableView(_ tableView: UITableView,
cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cellIdentifier = "SpeakerTableViewCell"
let cell = tableView.dequeueReusableCell(withIdentifier:
cellIdentifier, for: indexPath) as SpeakerTableViewCell
let speaker = speakers[indexPath.row]
cell.talkName.text = speaker.talkTitle
cell.speakerName.text = speaker.speaker
cell.speakerImage.image = speaker.img
return cell
}
iOS
iosApp/iosApp/SpeakerTableViewController.swift
iOS
business logic
model
parser
network
presentation
view
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conclusions
don’t forget to bring your own towel.
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- it’s in experimental state
- although there are projects in production
- you can spend some time resolving compilation issues
- specially if you try to target all platforms
- not possible to debug kotlin from Xcode
- lookout for plugins/ libraries updates
(in progress)
Kotlin Multiplatform
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- strong community
- a lot of people are using kotlin nowadays
- Google and JetBrains are pushing Kotlin in
- you can ask questions directly on https://kotlinlang.slack.com
- 2x faster to develop your features business logic
- 2x faster writing unit tests
- one tech stack
- consistency across platforms
(conclusions)
Kotlin Multiplatform
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- be extremely careful with all updates
- IDEA, jdk, kotlin, libraries - everything.
- start small, don’t try to reach 100% of shared logic
- keep versioning in mind
- remember that’s still on experimental state
(suggestions)
Kotlin Multiplatform
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- Kotlin Slack
- Android @ Portugal Slack
- Kotlin Official
- Kotlin Training
- Kotlin by:
https://jakewharton.com/presentations/
http://antonioleiva.com/kotlin
(useful links)
more information
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@cafonsomota
so long and thanks for all the fish