Migrating a mature code base to Kotlin

@geeky_android
Migrating a mature
codebase to Kotlin

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@geeky_android
Mandatory who-am-i
• Savvas Dalkitsis
• Principal Software Engineer for Apps @

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@geeky_android
Mandatory who-is-ASOS
“Our mission is to become the world’s number-one
online shopping destination for fashion-loving
20-somethings.”

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@geeky_android
Team structure
Director of technology – Web and Apps
Apps team
Web team
Platform lead Platform lead Principal Architect
ADM
ADM
ADM
BA
BA
BA
Android team
Team 1
Dev
Dev
QA
QA
. . .
. . .
Team 2
Dev
Dev
QA
QA
. . .
. . .
Team 3
Dev
Dev
QA
QA
. . .
. . .
Principal Engineer
iOS team
Team 1
Dev
Dev
QA
QA
. . .
. . .
Team 2
Dev
Dev
QA
QA
. . .
. . .
Team 3
Dev
Dev
QA
QA
. . .
. . .

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@geeky_android
A mature project
17,927 files

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@geeky_android
Mobile is important to us
• 75%+ traffic from mobile (web and apps)
• 60%+ revenue

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@geeky_android
• Butterknife
• RxJava2
• OkHttp
• Retrofit
• Espresso
• Kotlin?

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@geeky_android

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@geeky_android
Why do we ?
!

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@geeky_android
class Model {
private String name;
private String surname;
private int age;
private int height;
private Address address;
private Country country;
public String getName() {
return name;
}
public String getSurname() {
return surname;
}
public int getAge() {
return age;
}
public int getHeight() {
return height;
}
public Address getAddress() {
return address;
}

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@geeky_android
if (height != model.height) return false;
if (name != null ? !name.equals(model.name) : model.name != null) return false;
if (surname != null ? !surname.equals(model.surname) : model.surname != null) return false;
if (address != null ? !address.equals(model.address) : model.address != null) return false;
return country != null ? country.equals(model.country) : model.country == null;
}
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (surname != null ? surname.hashCode() : 0);
result = 31 * result + age;
result = 31 * result + height;
result = 31 * result + (address != null ? address.hashCode() : 0);
result = 31 * result + (country != null ? country.hashCode() : 0);
return result;
}
@Override
public String toString() {
return "Model{" +
"name='" + name + '\'' +
", surname='" + surname + '\'' +
", age=" + age +
", height=" + height +
", address=" + address +
", country=" + country +
'}';
}
}

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@geeky_android
data class Model(
var name: String,
var surname: String,
var age: Int,
var height: Int,
var address: Address,
var country: Country
)

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@geeky_android
class Model {
private int age;
private int height;
return name;
}
return surname;
}
return age;
}
return height;
}
return address;
}
public Country getCountry() {
return country;
}
public void setName(String name) {
this.name = name;
}
public void setSurname(String surname) {
this.surname = surname;
}
public void setAge(int age) {
this.age = age;
}
public void setHeight(int height) {
this.height = height;
}
public void setAddress(Address address) {
this.address = address;
}
public void setCountry(Country country) {
this.country = country;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Model model = (Model) o;
if (age != model.age) return false;
}
@Override
return result;
}
@Override
return "Model{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}

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@geeky_android
class Model {
private int age;
private int height;
public Model(Builder builder) {
name = builder.name;
surname = builder.surname;
age = builder.age;
height = builder.height;
address = builder.address;
country = builder.country;
}
return name;
}
return surname;
}
return age;
}
return height;
}
return address;
}
return country;
}
@Override
}
@Override
return result;
}
@Override
return "Model{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}

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@geeky_android
class Model {
private int age;
private int height;
public Model(Builder builder) {
name = builder.name;
surname = builder.surname;
age = builder.age;
height = builder.height;
address = builder.address;
country = builder.country;
}
return name;
}
return surname;
}
return age;
}
return height;
}
return address;
}
return country;
}
@Override
}
@Override
return result;
}
@Override
return "Model{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}
public static class Builder {
private int age;
private int height;
public static Builder model() {
return new Builder();
}
public Builder withName(String name) {
this.name = name;
return this;
}
public Builder withSurname(String surname) {
this.surname = surname;
return this;
}
public Builder withAge(int age) {
this.age = age;
return this;
}
public Builder withHeight(int height) {
this.height = height;
return this;
}
public Builder withAddress(Address address) {
this.address = address;
return this;
}
public Builder withCountry(Country country) {
this.country = country;
return this;
}
public Model build() {
return new Model(this);
}
}

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@geeky_android
data class Model(
var name: String,
var age: Int,
var height: Int,
)

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@geeky_android
data class Model(
var name: String,
var age: Int,
var height: Int,
)
data class Model(
val name: String,
val surname: String,
val age: Int,
val height: Int,
val address: Address,
val country: Country
)

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@geeky_android
How do I convince my ?
"

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@geeky_android
A small feature

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@geeky_android
A small isolated feature

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@geeky_android
¯\_(ϑ)_/¯
If things don’t work out

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@geeky_android
Where do I begin?
https://kotlinlang.org/docs/tutorials/koans.html

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@geeky_android
But WHERE do I begin?

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@geeky_android

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@geeky_android
Then what?

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@geeky_android
. . .
. . .

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@geeky_android
. . .

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@geeky_android

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@geeky_android
Cmd+Shift+A is your friend

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@geeky_android

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@geeky_android
#

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@geeky_android

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@geeky_android
class ReturnListActivity: ToolbarFragmentActivity() {
companion object {
@JvmStatic fun newIntent(activity: Activity)= Intent(activity, ReturnListActivity::class.java)
}
override fun getFragment() = ReturnListFragment()
override fun getToolbarTitle(): String? = getString(R.string.my_returns_header)
override fun getDisplayHomeAsUpEnabled(): Boolean = true
}

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@geeky_android
open class ReturnMethodPresenter : BasePresenter() {
private lateinit var orderDetails: OrderDetails
fun bindView(view: T, orderDetails: OrderDetails) {
super.setView(view)
this.orderDetails = orderDetails
}
fun onDropOffClicked() {
orderDetails.deliveryDetails.address?.let {
val customerBasicInfo = CustomerBasicInfo(it.firstName,
it.lastName, it.telephoneMobile, it.emailAddress)
val searchData = DropOffSearchData(it.postalCode, it.countryCode,
orderDetails.currencyCode, customerBasicInfo)
view.launchDropOffPointSearch(searchData)
}
}
}

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@geeky_android
How are we doing?

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@geeky_android
Is it all ☁ and %?

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@geeky_android
@PaperParcel
data class SocialConnection(val isConnected: Boolean = false,
val email: String? = null,
val nickname: String? = null,
var firstName: String? = null,
var lastName: String? = null,
val isLoggedIn: Boolean = false) : Parcelable {
companion object {
@JvmField val CREATOR = PaperParcelSocialConnection.CREATOR
}
override fun writeToParcel(dest: Parcel, flags: Int) {
PaperParcelSocialConnection.writeToParcel(this, dest, flags)
}
override fun describeContents() = 0
}

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@geeky_android

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@geeky_android
• Build times
• Switching branches

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@geeky_android
Show me some % % % %!!!

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@geeky_android
val age = retrievePersonAge() ?: 0
private fun retrievePersonAge(): Int? = …
val age = retrievePersonAge() ?: throw IllegalStateException("Can I haz age?")

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@geeky_android
val savvas = Person(
name = "Savvas",
age = confidential(),
address = ditto(),
email = "[email protected]",
country = uk()
)

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@geeky_android
data class Person(
val name: String?,
val age: Int,
val email: String?,
val address: Address?,
val country: Country?
)

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@geeky_android
data class Person(
val name: String?,
val age: Int,
val email: String?,
)
data class Person(
val name: String?,
val age: Int,
val email: String? = null,
)

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@geeky_android
name = "Savvas",
address = ditto(),
country = uk()
)

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@geeky_android
name = "Savvas",
address = ditto(),
country = uk()
)
val olderSavvas = savvas.copy(age = 50)

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@geeky_android
checkout().bagStockReservation?.outOfStockItems.orEmpty()
.filter { (it.price?.discount?.value ?: 0.0) > 10 }

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@geeky_android
fun main(args: Array) {
people().orEmpty().filter { it.age > 18 }
}
private fun people(): List? = null

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@geeky_android
println(people()
.map { it.age }
.filter { it > 18 }
.average())
println(people()
.filter { it.age > 18 }
.sumBy { it.age })
println(people()
.map { it.age }
.filter { it > 18 }
.reduce { total, current -> total + current })
// prints:
// 20
// 40
// 40
}
private fun people(): List = listOf(Person(age = 19), Person(age = 10), Person(age = 21))

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@geeky_android
Intent().navigateWith(someContext())
}
fun Intent.navigateWith(context: Context) {
if (context !is Activity) {
this.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
}
context.startActivity(this)
}

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@geeky_android
Intent().apply {
action = "someAction"
setClassName("my.awesome.package", ".MyAwesomeClass")
}.navigateWith(someContext())
}

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@geeky_android
class Model
interface ModelUseCase {
fun announceModelUpdated()
fun saveModel(model: Model)
// many more methods ...
}

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@geeky_android
class Model
}
class DebounceModelUseCase(windowMillis: Long, val delegate: ModelUseCase): ModelUseCase {
private val debouncer: BehaviorProcessor = BehaviorProcessor.create()
init {
debouncer.debounce(windowMillis, TimeUnit.MILLISECONDS)
.subscribe { delegate.announceModelUpdated() }
}
override fun announceModelUpdated() {
debouncer.onNext(Unit)
}
override fun saveModel(model: Model) {
delegate.saveModel(model)
}
}

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@geeky_android
class Model
}
class DebounceModelUseCase(windowMillis: Long, delegate: ModelUseCase): ModelUseCase by delegate {
private val debouncer: BehaviorProcessor = BehaviorProcessor.create()
init {
debouncer.debounce(windowMillis, TimeUnit.MILLISECONDS)
.subscribe { delegate.announceModelUpdated() }
}
override fun announceModelUpdated() {
debouncer.onNext(Unit)
}
}

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@geeky_android
and much much more
https://kotlinlang.org/docs/tutorials/koans.html

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@geeky_android
&
Questions?

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Migrating a mature code base to Kotlin

Migrating a mature code base to Kotlin

Savvas Dalkitsis

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