Kotlin 2 ½ Years Later

1.

Kotlin 2 ½ Years Later A brief story about how
Cody uses Kotlin.

2.

Started Android In 2011 Java and Eclipse were fun.

3.

Started Learning Kotlin At Yello Split my time about 25%
Kotlin and 75% Java at the time.

4.

Working Exclusively In Kotlin At ActiveCampaign We’re hiring. Message me
on engel.dev if you want to learn more.

5.

Time For Some Kotlin If you have questions during the
talk, message me on engel.dev.

6.

val typeInference: Int = 1 What I’m Not Talking About

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val typeInference = 1 What I’m Not Talking About

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data class Speaker(val name: String = "Cody") val speaker =
Speaker() val stringTemplates = """ Wow this is cool. Thanks, ${speaker.name} """.trimIndent() What I’m Not Talking About

9.

data class Speaker(val name: String = "Cody") val speaker =
Speaker() val stringTemplates = """ Wow this is cool. Thanks, ${speaker.name} """.trimIndent() What I’m Not Talking About

10.

fun conditionalExpressions(a: Int, b: Int): Int { if (a >
b) { return a } else { return b } } What I’m Not Talking About

11.

fun conditionalExpressions(a: Int, b: Int): Int { return if (a
> b) { a } else { b } } What I’m Not Talking About

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fun conditionalExpressions(a: Int, b: Int) = if (a > b)
a else b What I’m Not Talking About

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fun typeCasting(any: Any) { when (any) { is String ->
any.length is Map<*, *> -> any.entries is Int -> any + 16 } } What I’m Not Talking About

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class DefaultValues(number: Int = 0) fun defaultValues(defaultValues: DefaultValues = DefaultValues())
{ defaultValues() } What I’m Not Talking About

15.

Goodbye NPE if (nullDoesntExist != null) { } Kotlin greatly
reduces the chance that you will inadvertently cause a NullPointerException in production. engel.dev

16.

if (nullDoesntExist != null) { // Why check null if
it does // not exist in Kotlin? } Why Still Check For Null?

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package kotlin public open class KotlinNullPointerException : java.lang.NullPointerException { public
constructor() { /* compiled code */ } public constructor(message: kotlin.String?) { /* compiled code */ } } Because NPEs Still Exist.

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val stringWithNothing: String? = null if (stringWithNothing != null) Which
Do You Prefer? val stringWithNothing: String = “” stringWithNothing.isNotEmpty()

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val intWithNothing: Int? = null if (intWithNothing != null) Which
Do You Prefer? val intWithNothing: Int = -1 if (intWithNothing != -1)

20.

val intWithNothing: Int? = null if (intWithNothing != null) Which
Do You Prefer? val intWithNothing: Int = 0 if (intWithNothing != -1)

21.

if (possiblyNull == null) { // What do we do!?!?!?
}

22.

val possiblyNull: String? = null val definitelyNotNull = possiblyNull ?:
""

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""

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val possiblyNull: String? = null val definitelyNotNull = possiblyNull?.run {
println("Cool this wasn't null.") } ?: ""

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{ println("This used to be null.") "" }()

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val possiblyNull: String? = null val definitelyNotNull = possiblyNull?.let {
println("Cool this wasn't null.") } ?: { println("This used to be null.") "" }()

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val possiblyNull: String? = null val definitelyNotNull = possiblyNull?.let {
println("Cool this wasn't null.") } ?: { println("This used to be null.") "" }.invoke()

28.

Working With The NullPointerException data class LocalUser( val apiKey: String?
= null, val username: String? = null, val userId: Long? = null )

29.

data class LocalUser( val apiKey: String? = null, val username:
String? = null, val userId: Long? = null ) data class AuthenticationRecord( val apiKey: String, val username: String, val userId: Long )

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data class AuthenticationRecord( val apiKey: String, val username: String, val
userId: Long ) val localUser = LocalUser() val authRecord = AuthenticationRecord( apiKey = localUser.apiKey, username = localUser.username, userId = localUser.userId )

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userId: Long ) val localUser = LocalUser() val authRecord = AuthenticationRecord( apiKey = localUser.apiKey, username = localUser.username, userId = localUser.userId ) Required: String, Found String?

32.

userId: Long ) val localUser = LocalUser() val authRecord = AuthenticationRecord( apiKey = localUser.apiKey, username = localUser.username, userId = localUser.userId ) Required: String, Found String? Required: String, Found String?

33.

userId: Long ) val localUser = LocalUser() val authRecord = AuthenticationRecord( apiKey = localUser.apiKey, username = localUser.username, userId = localUser.userId ) Required: String, Found String? Required: String, Found String? Required: String, Found String?

34.

val localUser = LocalUser() val authRecord = AuthenticationRecord( apiKey =
localUser.apiKey ?: "", username = localUser.username ?: "", userId = localUser.userId ?: -1 ) val authRecord = AuthenticationRecord( apiKey = localUser.apiKey, username = localUser.username, userId = localUser.userId ) Required: String, Found String? Required: String, Found String? Required: String, Found String?

35.

val localUser = LocalUser() val authRecord = AuthenticationRecord( apiKey =
localUser.apiKey!!, username = localUser.username!!, userId = localUser.userId!! ) val localUser = LocalUser() val authRecord = AuthenticationRecord( apiKey = localUser.apiKey ?: "", username = localUser.username ?: "", userId = localUser.userId ?: -1 )

36.

apiKey = localUser.apiKey!!, username = localUser.username!!, userId = localUser.userId!! )
val authRecord = try { AuthenticationRecord( apiKey = localUser.apiKey!!, username = localUser.username!!, userId = localUser.userId!! ) } catch (exception: KotlinNullPointerException) { // Provide an error to the user because they // aren't authenticated. }

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// Provide an error to the user because they //
aren't authenticated. } val authRecord = if ( localUser.apiKey != null && localUser.username != null && localUser.userId != null) { AuthenticationRecord( localUser.apiKey, localUser.username, localUser.userId ) } else { // Provide an error to the user because they // aren't authenticated. }

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} else { // Provide an error to the user
because they // aren't authenticated. } val authRecord = try { AuthenticationRecord( apiKey = localUser.apiKey!!, username = localUser.username!!, userId = localUser.userId!! ) } catch (exception: KotlinNullPointerException) { // Provide an error to the user because they // aren't authenticated. }

39.

This is Not Jake Wharton Approved… …so that was kind
of

40.

Kotlin Defaults To Non-Null For Java APIs… …sorry.

41.

Data Classes data class Cat( val name: String = "Tina",
val age: Int = 4 ) val tina = Cat() tina.name // Tina tina.age // 4 tina.equals(Cat(name = "Tina")) // true tina.hashCode() // some number val (name, age) = tina val tinaIsOlder = tina.copy(age = 5) // older Sometimes classes exist for the sole purpose of containing data. This is where data classes shine. engel.dev

42.

class Cat( val name: String = "Tina", val age: Int
= 4 ) val tina = Cat() tina.name // Tina tina.age // 4 tina.equals(Cat(name = "Tina")) // true tina.hashCode() // some number val (name, age) = tina val tinaIsOlder = tina.copy(age = 5) // older Normal Boring Class.

43.

= 4 ) val tina = Cat() tina.name // Tina tina.age // 4 tina.equals(Cat(name = "Tina")) // false tina.hashCode() // some number val (name, age) = tina val tinaIsOlder = tina.copy(age = 5) // older Normal Boring Class.

44.

= 4 ) val tina = Cat() tina.name // Tina tina.age // 4 tina.equals(Cat(name = "Tina")) // false tina.hashCode() // some number, but calculated differently val (name, age) = tina val tinaIsOlder = tina.copy(age = 5) // older Normal Boring Class.

45.

= 4 ) val tina = Cat() tina.name // Tina tina.age // 4 tina.equals(Cat(name = "Tina")) // false tina.hashCode() // some number, but calculated differently val (name, age) = tina val tinaIsOlder = tina.copy(age = 5) // older Normal Boring Class.

46.

= 4 ) val tina = Cat() tina.name // Tina tina.age // 4 tina.equals(Cat(name = "Tina")) // false tina.hashCode() // some number, but calculated differently val (name, age) = tina val tinaIsOlder = tina.copy(age = 5) Normal Boring Class.

47.

= 4, currentlyHungry: Boolean ) Normal Boring Class.

48.

data class Cat( val name: String = "Tina", val age:
Int = 4, currentlyHungry: Boolean ) Exciting Data Class.

49.

Int = 4, currentlyHungry: Boolean ) " Exciting Data Class.

50.

Int = 4, currentlyHungry: Boolean ) " Exciting Data Class. Data class primary constructor must have only property (val/var) parameters

51.

Int = 4 ) Using Data Classes.

52.

Int = 4 ) val shouldBeConsistent = tina.hashCode() Using Data Classes.

53.

Int = 4 ) val shouldBeTrue = tina.equals(Cat(name = “Tina")) val shouldBeConsistent = tina.hashCode() Using Data Classes.

54.

Int = 4 ) val tinaIsOlder = tina.copy(age = 5) val shouldBeTrue = tina.equals(Cat(name = “Tina")) val shouldBeConsistent = tina.hashCode() Using Data Classes.

55.

Sealed Classes sealed class DealCustomFieldValue( val fieldId: Long?, val value:
String?, val title: String?, val order: Long?, val type: String?, val fieldValueId: Long? ) { data class StandardFieldValue( private val _fieldId: Long?, private val _value: String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long? ) : DealCustomFieldValue( _fieldId, _value, _title, _order, _type, _fieldValueId ) data class NumberFieldValue( private val _fieldId: Long?, private val _value: String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long? ) : DealCustomFieldValue( _fieldId, _value, _title, _order, _type, _fieldValueId ) data class CurrencyFieldValue( private val _fieldId: Long?, private val _value: String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long?, val fieldCurrency: String?, val currencyPosition: String? ) : DealCustomFieldValue( _fieldId, _value, _title, _order, _type, _fieldValueId ) } Used for representing restricted class hierarchies. They are like an extension on enum classes where sub- classes can have multiple instances available at a time. engel.dev

56.

sealed class DealCustomFieldValue( val fieldId: Long?, val value: String?, val
title: String?, val order: Long?, val type: String?, val fieldValueId: Long? ) { data class StandardFieldValue(

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) { data class StandardFieldValue( private val _fieldId: Long?, private
val _value: String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long? ) : DealCustomFieldValue( _fieldId,

58.

private val _type: String?, private val _fieldValueId: Long? ) :
DealCustomFieldValue( _fieldId, _value, _title, _order, _type, _fieldValueId )

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data class CurrencyFieldValue( private val _fieldId: Long?, private val _value:
String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long?, val fieldCurrency: String?, val currencyPosition: String? ) : DealCustomFieldValue(

60.

val fieldCurrency: String?, val currencyPosition: String? ) : DealCustomFieldValue( _fieldId,
_value, _title, _order, _type, _fieldValueId ) }

61.

title: String?, val order: Long?, val type: String?, val fieldValueId: Long? ) { data class StandardFieldValue(

62.

sealed class DealCustomFieldValue { abstract val fieldId: Long? abstract val
value: String? abstract val title: String? abstract val order: Long? abstract val type: String? abstract val fieldValueId: Long? data class StandardFieldValue( override val fieldId: Long?,

63.

data class StandardFieldValue( override val fieldId: Long?, override val value:
String?, override val title: String?, override val order: Long?, override val type: String?, override val fieldValueId: Long? ) : DealCustomFieldValue() data class NumberFieldValue( override val fieldId: Long?,

64.

data class CurrencyFieldValue( override val fieldId: Long?, override val value:
String?, override val title: String?, override val order: Long?, override val type: String?, override val fieldValueId: Long?, val fieldCurrency: String?, val currencyPosition: String? ) : DealCustomFieldValue()

65.

title: String?, val order: Long?, val type: String?, val fieldValueId: Long? ) { data class StandardFieldValue( private val _fieldId: Long?, private val _value: String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long? ) : DealCustomFieldValue( _fieldId, _value, _title, _order, _type, _fieldValueId ) data class NumberFieldValue( private val _fieldId: Long?, private val _value: String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long? ) : DealCustomFieldValue( _fieldId, _value, _title, _order, _type, _fieldValueId ) data class CurrencyFieldValue( private val _fieldId: Long?, private val _value: String?, private val _title: String?, private val _order: Long?, private val _type: String?, private val _fieldValueId: Long?, val fieldCurrency: String?, val currencyPosition: String? ) : DealCustomFieldValue( _fieldId, _value, _title, _order, _type, _fieldValueId ) } sealed class DealCustomFieldValue { abstract val fieldId: Long? abstract val value: String? abstract val title: String? abstract val order: Long? abstract val type: String? abstract val fieldValueId: Long? data class StandardFieldValue( override val fieldId: Long?, override val value: String?, override val title: String?, override val order: Long?, override val type: String?, override val fieldValueId: Long? ) : DealCustomFieldValue() data class NumberFieldValue( override val fieldId: Long?, override val value: String?, override val title: String?, override val order: Long?, override val type: String?, override val fieldValueId: Long? ) : DealCustomFieldValue() data class CurrencyFieldValue( override val fieldId: Long?, override val value: String?, override val title: String?, override val order: Long?, override val type: String?, override val fieldValueId: Long?, val fieldCurrency: String?, val currencyPosition: String? ) : DealCustomFieldValue() }

66.

fun mapCustomFieldResponse(field: DealCustomFieldValue): StandardFieldData { return field.run { when (this)
{ is DealCustomFieldValue.CurrencyFieldValue -> { createStandardField( title = title ?: "", body = currencyUtil.serverValueToDisplayValue( value?.toDouble(), currencyPosition, fieldCurrency ), leftIcon = R.drawable.ic_short_text ) } is DealCustomFieldValue.NumberFieldValue -> createStandardField( title = title ?: "", body = value.toDoubleFormatTwoDecimalPlaces(), leftIcon = R.drawable.ic_short_text ) is DealCustomFieldValue.StandardFieldValue -> createStandardField( title = title ?: “", body = value ?: “", leftIcon = R.drawable.ic_short_text ) } } }

67.

when (this) { is DealCustomFieldValue.CurrencyFieldValue -> {} is DealCustomFieldValue.NumberFieldValue ->
{} is DealCustomFieldValue.StandardFieldValue -> {} }

68.

{} is DealCustomFieldValue.StandardFieldValue -> {} else -> {} }

69.

{} is DealCustomFieldValue.StandardFieldValue -> {} else -> { /* not necessary */ } }

70.

{ createStandardField( title = title ?: "", body = value.toDoubleFormatTwoDecimalPlaces(), leftIcon = R.drawable.ic_short_text ) } is DealCustomFieldValue.StandardFieldValue -> {} }

71.

{ createStandardField( title = title ?: "", body = value.toDoubleFormatTwoDecimalPlaces(), leftIcon = R.drawable.ic_short_text ) } is DealCustomFieldValue.StandardFieldValue -> { createStandardField( title = title ?: “", body = value ?: “", leftIcon = R.drawable.ic_short_text ) } }

72.

when (this) { is DealCustomFieldValue.CurrencyFieldValue -> { createStandardField( title =
title ?: "", body = currencyUtil.serverValueToDisplayValue( value?.toDouble(), currencyPosition, fieldCurrency ), leftIcon = R.drawable.ic_short_text ) } is DealCustomFieldValue.NumberFieldValue -> { createStandardField( title = title ?: "", body = value.toDoubleFormatTwoDecimalPlaces(), leftIcon = R.drawable.ic_short_text ) }

73.

Collections.kt val cats = listOf<Cat>() cats.map { it.age } //
List of Ages. cats.filter { it.age > 4 } // List of Cats older than 4. cats.last { it.name == "Tina" } // Last Cat named Tina. cats.slice(5..10) // Cats within the range of 5 to 10. cats.takeLast(15) // The last 15 Cats in the list. cats.groupBy { it.age } // Cats grouped by their age. cats.random() // Random Cat from the list. The Collections framework that ships with Kotlin makes working with collections a breeze. engel.dev

74.

val cats = listOf<Cat>() cats.map { it.age } // List
of Ages. cats.filter { it.age > 4 } // List of Cats older than 4. cats.last { it.name == "Tina" } // Last Cat named Tina. cats.slice(5..10) // Cats within the range of 5 to 10. cats.takeLast(15) // The last 15 Cats in the list. cats.groupBy { it.age } // Group Cats by their age. cats.random() // Random Cat from the list. Collections.kt Abbreviated.

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cats.filter { it.age > 4 } // List of Cats
older than 4. cats.last { it.name == "Tina" } // Last Cat named Tina. cats.slice(5..10) // Cats within the range of 5 to 10. cats.takeLast(15) // The last 15 Cats in the list. cats.groupBy { it.age } // Group Cats by their age. cats.random() // Random Cat from the list. cats .filter { it.age > 4 } .random() // Random Cat, older than 4.

83.

// Random Cat, from the last 20 elements, older than
4. cats .filter { it.age > 4 } .takeLast(20) .random() cats.groupBy { it.age } // Group Cats by their age. cats.random() // Random Cat from the list. cats .filter { it.age > 4 } .random() // Random Cat, older than 4.

84.

4. cats .filter { it.age > 4 } .takeLast(20) .random() // Random Cat, older than 4, from the last 20 elements. cats .takeLast(20) .filter { it.age > 4 } .random()

85.

4. cats .filter { it.age > 4 } .takeLast(20) .random() cats .takeLast(20) // New list of 20 cats. .filter { it.age > 4 } // New list containing only cats older than 4. .random()

86.

.takeLast(20) // New list of 20 cats. .filter { it.age
> 4 } // New list containing only cats older than 4. .random() cats.reversed().asSequence() .take(20) .filter { it.age > 4 } .toList() .random()

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cats.reversed().asSequence() .take(20) .filter { it.age > 4 } .toList() .random()
sealed class FieldValue<T> { abstract val value: T data class NumericField(override val value: Long) : FieldValue<Long>() data class MoneyField(override val value: Double) : FieldValue<Double>() data class TextField(override val value: String) : FieldValue<String>() data class MultiSelect<T>(override val value: List<T>) : FieldValue<List<T>>() }

91.

abstract val value: T data class NumericField(override val value: Long)
: FieldValue<Long>() data class MoneyField(override val value: Double) : FieldValue<Double>() data class TextField(override val value: String) : FieldValue<String>() data class MultiSelect<T>(override val value: List<T>) : FieldValue<List<T>>() } val fieldValues = listOf<FieldValue>() val fieldGroup = mutableMapOf<KClass, MutableList<FieldValue>>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }

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data class TextField(override val value: String) : FieldValue<String>() data class
MultiSelect<T>(override val value: List<T>) : FieldValue<List<T>>() } val fieldValues = listOf<FieldValue>() val fieldGroup = mutableMapOf<KClass, MutableList<FieldValue>>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues } val fieldValues = listOf<FieldValue>() val fieldGroup = fieldValues.groupBy { it::class }

100.

Extensions editText.setTextIfChanged(“blah") view.verticalPositionInParent moshi.toJson(EmailBody("subject", “body")) activeCampaignAnalytics.markComplete() intent.conversationUri In Java extending
functionality on concrete classes require static Util classes. Kotlin allows us to add functionality to concrete classes through extensions. engel.dev

101.

editText.setTextIfChanged(“blah") view.verticalPositionInParent moshi.toJson(EmailBody("subject", “body")) activeCampaignAnalytics.markComplete() intent.conversationUri

102.

fun TextView.setTextIfChanged(text: CharSequence) { if (this.text.toString() != text) { setTextKeepState(text)
} } editText.setTextIfChanged(“blah”) view.verticalPositionInParent moshi.toJson(EmailBody("subject", “body")) activeCampaignAnalytics.markComplete() intent.conversationUri

103.

editText.setTextIfChanged(“blah”) val View.verticalPositionInParent: Int get() { val offsetViewBounds = Rect()
parentAsViewGroup .offsetDescendantRectToMyCoords( this, offsetViewBounds ) return offsetViewBounds.top } view.verticalPositionInParent moshi.toJson(EmailBody("subject", “body")) activeCampaignAnalytics.markComplete()

104.

.offsetDescendantRectToMyCoords( this, offsetViewBounds ) return offsetViewBounds.top } view.verticalPositionInParent inline fun
<reified T> Moshi.toJson(value: T): String { val adapter: JsonAdapter<T> = adapter(T::class.java) return adapter.toJson(value) } moshi.toJson(EmailBody("subject", “body”)) activeCampaignAnalytics.markComplete() intent.conversationUri

105.

view.verticalPositionInParent inline fun <reified T> Moshi.toJson(value: T): String { val
adapter: JsonAdapter<T> = adapter(T::class.java) return adapter.toJson(value) } moshi.toJson(EmailBody("subject", “body”)) fun ActiveCampaignAnalytics.markComplete() { sendEvent(completeConversationEvent) } activeCampaignAnalytics.markComplete() intent.conversationUri

106.

view.verticalPositionInParent inline fun <reified T> Moshi.toJson(value: T): String { val
adapter: JsonAdapter<T> = adapter(T::class.java) return adapter.toJson(value) } moshi.toJson(EmailBody("subject", “body”)) fun ActiveCampaignAnalytics.markComplete() { sendEvent(completeConversationEvent) } activeCampaignAnalytics.markComplete() private val Intent.conversationUri: String get() = getStringExtra(EXTRA_CONVERSATION_URI) intent.conversationUri

107.

Class Delegation abstract class AbstractActivity : AppCompatActivity(), DisposableHandler by DisposableHandlerReal(),
KeyboardHandler by KeyboardHandlerReal() { Delegation allows for code reuse in a manner that prefers composition over inheritance. engel.dev

108.

abstract class AbstractActivity : AppCompatActivity(), DisposableHandler by DisposableHandlerReal(), KeyboardHandler by
KeyboardHandlerReal() {}

109.

KeyboardHandlerReal() { override fun addDisposable(disposable: Disposable) {} override fun addDisposables(vararg disposables: Disposable) {} override fun clearDisposables() {} }

110.

KeyboardHandlerReal() { override fun addDisposable(disposable: Disposable) { compositeDisposable.add(disposable) } override fun addDisposables(vararg disposables: Disposable) { compositeDisposable.addAll(*disposables) } override fun clearDisposables() { compositeDisposable.clear() } }

111.

KeyboardHandlerReal() {} class DisposableHandlerReal : DisposableHandler { private val compositeDisposable = CompositeDisposable() override fun addDisposable(disposable: Disposable) { compositeDisposable.add(disposable) } override fun addDisposables(vararg disposables: Disposable) { compositeDisposable.addAll(*disposables) } override fun clearDisposables() { compositeDisposable.clear() } }

112.

abstract class AbstractViewModel : ViewModel(), DisposableHandler by DisposableHandlerReal() class DisposableHandlerReal
: DisposableHandler { private val compositeDisposable = CompositeDisposable() override fun addDisposable(disposable: Disposable) { compositeDisposable.add(disposable) } override fun addDisposables(vararg disposables: Disposable) { compositeDisposable.addAll(*disposables) } override fun clearDisposables() { compositeDisposable.clear() } }

113.

KeyboardHandlerReal() {}

114.

KeyboardHandlerReal() { override fun showKeyboard(context: Context) {} override fun dismissKeyboard(context: Context, view: View) {} }

115.

KeyboardHandlerReal() { override fun showKeyboard(context: Context) { val inputMethodManager = context .getSystemService(Context.INPUT_METHOD_SERVICE) inputMethodManager.toggleSoftInput( InputMethodManager.SHOW_FORCED, InputMethodManager.HIDE_IMPLICIT_ONLY ) } override fun dismissKeyboard(context: Context, view: View) { val inputMethodManager = context .getSystemService(Context.INPUT_METHOD_SERVICE) inputMethodManager.hideSoftInputFromWindow(view.windowToken, 0) } }

116.

KeyboardHandlerReal() {} class KeyboardHandlerReal : KeyboardHandler { override fun showKeyboard(context: Context) { val inputMethodManager = context .getSystemService(Context.INPUT_METHOD_SERVICE) inputMethodManager.toggleSoftInput( InputMethodManager.SHOW_FORCED, InputMethodManager.HIDE_IMPLICIT_ONLY ) } override fun dismissKeyboard(context: Context, view: View) { val inputMethodManager = context .getSystemService(Context.INPUT_METHOD_SERVICE) inputMethodManager.hideSoftInputFromWindow(view.windowToken, 0) } }

117.

class AbstractFragment : Fragment(), KeyboardHandler by KeyboardHandlerReal() {} class KeyboardHandlerReal
: KeyboardHandler { override fun showKeyboard(context: Context) { val inputMethodManager = context .getSystemService(Context.INPUT_METHOD_SERVICE) inputMethodManager.toggleSoftInput( InputMethodManager.SHOW_FORCED, InputMethodManager.HIDE_IMPLICIT_ONLY ) } override fun dismissKeyboard(context: Context, view: View) { val inputMethodManager = context .getSystemService(Context.INPUT_METHOD_SERVICE) inputMethodManager.hideSoftInputFromWindow(view.windowToken, 0) } }

118.

class Example { var property: String by Delegate() } Property
Delegation

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class Example { var property: String by Delegate() } class
Delegate { operator fun getValue(thisRef: Any?, property: KProperty<*>): String operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) }

120.

class Example { var property: String by Delegate() } class
Delegate { operator fun getValue(thisRef: Any?, property: KProperty<*>): String { return "$thisRef, thank you for delegating '${property.name}' to me!" } operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) { println("$value has been assigned to '${property.name}' in $thisRef.") } } class Delegate { operator fun getValue(thisRef: Any?, property: KProperty<*>): String operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) }

121.

val lazyInitialization by lazy { """ This String Is Created
When First Needed Then Cached And Reused In The Future """.trimIndent() } operator fun getValue(thisRef: Any?, property: KProperty<*>): String { return "$thisRef, thank you for delegating '${property.name}' to me!" } operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) { println("$value has been assigned to '${property.name}' in $thisRef.") } }

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""".trimIndent() } /* * Copyright 2010-2018 JetBrains s.r.o. Use of
this source code is governed by the Apache 2.0 license * that can be found in the license/LICENSE.txt file. */ @file:kotlin.jvm.JvmName("LazyKt") @file:kotlin.jvm.JvmMultifileClass package kotlin /** * Creates a new instance of the [Lazy] that uses the specified initialization function [initializer] * and the default thread-safety mode [LazyThreadSafetyMode.SYNCHRONIZED]. * * If the initialization of a value throws an exception, it will attempt to reinitialize the value at next access. * * Note that the returned instance uses itself to synchronize on. Do not synchronize from external code on

123.

* If the initialization of a value throws an exception,
it will attempt to reinitialize the value at next access. * * Note that the returned instance uses itself to synchronize on. Do not synchronize from external code on * the returned instance as it may cause accidental deadlock. Also this behavior can be changed in the future. */ public actual fun <T> lazy(initializer: () -> T): Lazy<T> = SynchronizedLazyImpl(initializer) /** * Creates a new instance of the [Lazy] that uses the specified initialization function [initializer] * and thread-safety [mode]. * * If the initialization of a value throws an exception, it will attempt to reinitialize the value at next access. * * Note that when the [LazyThreadSafetyMode.SYNCHRONIZED] mode is specified the returned instance uses itself * to synchronize on. Do not synchronize from external code on the returned instance as it may cause accidental deadlock.

124.

*/ public actual fun <T> lazy(lock: Any?, initializer: () ->
T): Lazy<T> = SynchronizedLazyImpl(initializer, lock) private class SynchronizedLazyImpl<out T>(initializer: () -> T, lock: Any? = null) : Lazy<T>, Serializable { private var initializer: (() -> T)? = initializer @Volatile private var _value: Any? = UNINITIALIZED_VALUE // final field is required to enable safe publication of constructed instance private val lock = lock ?: this override val value: T get() { val _v1 = _value if (_v1 !== UNINITIALIZED_VALUE) { @Suppress("UNCHECKED_CAST") return _v1 as T } return synchronized(lock) { val _v2 = _value if (_v2 !== UNINITIALIZED_VALUE) {

125.

return newValue } } @Suppress("UNCHECKED_CAST") return _value as T }
override fun isInitialized(): Boolean = _value !== UNINITIALIZED_VALUE override fun toString(): String = if (isInitialized()) value.toString() else "Lazy value not initialized yet." private fun writeReplace(): Any = InitializedLazyImpl(value) companion object { private val valueUpdater = java.util.concurrent.atomic.AtomicReferenceFieldUpdater.newUpdater( SafePublicationLazyImpl::class.java, Any::class.java, "_value" ) } }

126.

Higher Order Functions fun randomerNumber(randomNumber: () -> Long): () ->
Long { return { randomNumber() * randomNumber() } } randomerNumber { Random.nextLong() }() Mostly used for passing a function into another function. However you can return a function from a function too. engel.dev

127.

Sandwich Code The why behind Higher Order Functions.

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None

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None

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None

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None

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None

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Boring Boring

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Boring Boring Interesting

135.

val startTime = System.currentTimeMillis() for (i in 0..100000) { println("Cat:
${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime

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fun benchmark(blockOfCode: () -> Unit): Long { val startTime =
System.currentTimeMillis() blockOfCode.invoke() val endTime = System.currentTimeMillis() return endTime - startTime } println("Cat: ${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime

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System.currentTimeMillis() blockOfCode() val endTime = System.currentTimeMillis() return endTime - startTime } println("Cat: ${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime

145.

benchmark({ for (i in 0..100000) { println("Cat: ${Cat()}") } }
val endTime = System.currentTimeMi return endTime - startTime }

146.

benchmark { for (i in 0..100000) { println("Cat: ${Cat()}") }
} val endTime = System.currentTimeMi return endTime - startTime }

147.

fun generateCats() { for (i in 0..100000) { println("Cat: ${Cat()}")
} } benchmark(::generateCats) } }

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150.

interface MutableListViewModel<T> : ListViewModel<T> { var dataSetChanges: ((change: DataSetChange) ->
Unit)? fun addItem(item: T) fun moveItem(item: T, newPosition: Int) fun removeItem(item: T) }

151.

interface MutableListViewModel<T> : ListViewModel<T> { var dataSetChanges: ((change: DataSetChange) ->
Unit)? fun addItem(item: T) fun moveItem(item: T, newPosition: Int) fun removeItem(item: T) }

152.

class MutableListViewModelDelegate<T>( initialItems: List<T> = emptyList() ) : MutableListViewModel<T> {
private val items = mutableListOf<T>() .apply { addAll(initialItems) } override var dataSetChanges: ((change: DataSetChange) -> Unit)? = null override val itemCount: Int = items.size override fun get(position: Int): T = items[position] override fun addItem(item: T) { items.add(item) dataSetChanges?.invoke(DataSetChange.Inserted(items.size, 1)) } override fun moveItem(item: T, newPosition: Int) { val from = items.indexOf(item) items.removeAt(from) items.add(newPosition, item) dataSetChanges?.invoke(DataSetChange.Moved(from, newPosition)) } override fun removeItem(item: T) { val index = items.indexOf(item) items.removeAt(index) dataSetChanges?.invoke(DataSetChange.Removed(index, 1)) } }

153.

private val items = mutableListOf<T>() .apply { addAll(initialItems) } override var dataSetChanges: ((change: DataSetChange) -> Unit)? = null override val itemCount: Int = items.size override fun get(position: Int): T = items[position] override fun addItem(item: T) { items.add(item) dataSetChanges?.invoke(DataSetChange.Inserted(items.size, 1)) } override fun moveItem(item: T, newPosition: Int) { val from = items.indexOf(item) items.removeAt(from) items.add(newPosition, item) dataSetChanges?.invoke(DataSetChange.Moved(from, newPosition)) } override fun removeItem(item: T) { val index = items.indexOf(item) items.removeAt(index) dataSetChanges?.invoke(DataSetChange.Removed(index, 1)) } }

154.

override var dataSetChanges: ((change: DataSetChange) -> Unit)? = null override fun addItem(item: T) { dataSetChanges?.invoke(DataSetChange.Inserted(items.size, 1)) } override fun moveItem(item: T, newPosition: Int) { dataSetChanges?.invoke(DataSetChange.Moved(from, newPosition)) } override fun removeItem(item: T) { dataSetChanges?.invoke(DataSetChange.Removed(index, 1)) } }

155.

sealed class DataSetChange { object All : DataSetChange() data class
Changed(val positionStart: Int, val itemCount: Int = 1) : DataSetChange() data class Inserted(val positionStart: Int, val itemCount: Int = 1) : DataSetChange() data class Moved(val from: Int, val to: Int) : DataSetChange() data class Removed(val positionStart: Int, val itemCount: Int = 1) : DataSetChange() }

156.

abstract class ListViewModelAdapter<T, VH : ListViewModelAdapter.ViewHolder<T>> : RecyclerView.Adapter<VH>() { protected
abstract val listViewModel: ListViewModel<T> val dataSetChanges: (change: DataSetChange) -> Unit = { when (it) { is DataSetChange.Inserted -> notifyItemRangeInserted(it.positionStart, it.itemCount) is DataSetChange.Moved -> notifyItemMoved(it.from, it.to) is DataSetChange.Removed -> notifyItemRangeRemoved(it.positionStart, it.itemCount) is DataSetChange.Changed -> notifyItemRangeChanged(it.positionStart, it.itemCount) is DataSetChange.All -> notifyDataSetChanged() } } override fun getItemCount(): Int = listViewModel.itemCount override fun onBindViewHolder(holder: VH, position: Int) { holder.bind(listViewModel[position]) } }

157.

abstract class ListViewModelAdapter<T, VH : ListViewModelAdapter.ViewHolder<T>> : RecyclerView.Adapter<VH>() { protected
abstract val listViewModel: ListViewModel<T> val dataSetChanges: (change: DataSetChange) -> Unit = { when (it) { is DataSetChange.Inserted -> notifyItemRangeInserted(it.positionStart, it.itemCount) is DataSetChange.Moved -> notifyItemMoved(it.from, it.to) is DataSetChange.Removed -> notifyItemRangeRemoved(it.positionStart, it.itemCount) is DataSetChange.Changed -> notifyItemRangeChanged(it.positionStart, it.itemCount) is DataSetChange.All -> notifyDataSetChanged() } } override fun getItemCount(): Int = listViewModel.itemCount override fun onBindViewHolder(holder: VH, position: Int) { holder.bind(listViewModel[position]) } }

158.

abstract class ListViewModelAdapter<T, VH : ListViewModelAdapter.ViewHolder<T>> : RecyclerView.Adapter<VH>() { val
dataSetChanges: (change: DataSetChange) -> Unit = { when (it) { is DataSetChange.Inserted -> notifyItemRangeInserted(it.positionStart, it.itemCount) is DataSetChange.Moved -> notifyItemMoved(it.from, it.to) is DataSetChange.Removed -> notifyItemRangeRemoved(it.positionStart, it.itemCount) is DataSetChange.Changed -> notifyItemRangeChanged(it.positionStart, it.itemCount) is DataSetChange.All -> notifyDataSetChanged() } } }

159.

viewModelStub.dataSetChanges = adapter.dataSetChanges

160.

Unit Testing If you don’t want to ship Kotlin to
production, then start with your CI/CD process. class LoginViewModelTest : ViewModelTest() { @MockK private lateinit var authenticationRepository: Authenti @MockK private lateinit var stringLoader: StringLoader @MockK private lateinit var telemetry: Telemetry @RelaxedMockK private lateinit var analytics: ActiveCampaignAnalytics private lateinit var subject: LoginViewModel private val viewStateAssertion = ViewStateAssertion<Log private val accountTextChanges by lazy { EventObservabl private val usernameTextChanges by lazy { EventObservab private val passwordTextChanges by lazy { EventObservab private val domainTextChanges by lazy { EventObservable private val loginClicks by lazy { EventObservable<Any>( private val textChange by lazy { randomString() } private val errorMessage by lazy { randomString() } private val genericErrorMessage by lazy { randomString( private val invalidRequestErrorMessage by lazy { random private val noPermissionsErrorMessage by lazy { randomS engel.dev

161.

class LoginViewModelTest : ViewModelTest() { @MockK private lateinit var authenticationRepository:
AuthenticationRepository @MockK private lateinit var stringLoader: StringLoader @MockK private lateinit var telemetry: Telemetry @RelaxedMockK private lateinit var analytics: ActiveCampaignAnalytics private lateinit var subject: LoginViewModel private val viewStateAssertion = ViewStateAssertion<LoginViewModel.State>() private val accountTextChanges by lazy { EventObservable<CharSequence>() } private val usernameTextChanges by lazy { EventObservable<CharSequence>() } private val passwordTextChanges by lazy { EventObservable<CharSequence>() } private val domainTextChanges by lazy { EventObservable<CharSequence>() } private val loginClicks by lazy { EventObservable<Any>() } private val textChange by lazy { randomString() } private val errorMessage by lazy { randomString() } private val genericErrorMessage by lazy { randomString() } private val invalidRequestErrorMessage by lazy { randomString() } private val noPermissionsErrorMessage by lazy { randomString() } private val accountExpiredErrorMessage by lazy { randomString() } private val trace by lazy { mockk<Trace>() }

162.

ss LoginViewModelTest : ViewModelTest() { @MockK private lateinit var authenticationRepository:
AuthenticationRepository @MockK private lateinit var stringLoader: StringLoader @MockK private lateinit var telemetry: Telemetry @RelaxedMockK private lateinit var analytics: ActiveCampaignAnalytics private lateinit var subject: LoginViewModel private val viewStateAssertion = ViewStateAssertion<LoginViewModel.State>() private val accountTextChanges by lazy { EventObservable<CharSequence>() } private val usernameTextChanges by lazy { EventObservable<CharSequence>() } private val passwordTextChanges by lazy { EventObservable<CharSequence>() } private val domainTextChanges by lazy { EventObservable<CharSequence>() } private val loginClicks by lazy { EventObservable<Any>() } private val textChange by lazy { randomString() } private val errorMessage by lazy { randomString() } private val genericErrorMessage by lazy { randomString() } private val invalidRequestErrorMessage by lazy { randomString() } private val noPermissionsErrorMessage by lazy { randomString() } private val accountExpiredErrorMessage by lazy { randomString() } private val trace by lazy { mockk<Trace>() } MockKAnnotations.init(this)

163.

private val viewStateAssertion = ViewStateAssertion<LoginViewModel.State>() private val accountTextChanges by lazy
{ EventObservable<CharSequence>() } private val usernameTextChanges by lazy { EventObservable<CharSequence>() } private val passwordTextChanges by lazy { EventObservable<CharSequence>() } private val domainTextChanges by lazy { EventObservable<CharSequence>() } private val loginClicks by lazy { EventObservable<Any>() } private val textChange by lazy { randomString() } private val errorMessage by lazy { randomString() } private val genericErrorMessage by lazy { randomString() } private val invalidRequestErrorMessage by lazy { randomString() } private val noPermissionsErrorMessage by lazy { randomString() } private val accountExpiredErrorMessage by lazy { randomString() } private val trace by lazy { mockk<Trace>() } private fun prepareTelemetry() { every { telemetry.startTrace(any()) } returns trace every { trace.putAttribute(any(), any()) } just Runs every { telemetry.endTrace(trace) } just Runs }

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166.

= ViewStateAssertion<LoginViewModel.State>() by lazy { EventObservable<CharSequence>() } s by lazy
{ EventObservable<CharSequence>() } s by lazy { EventObservable<CharSequence>() } by lazy { EventObservable<CharSequence>() } y { EventObservable<Any>() } { randomString() } zy { randomString() } e by lazy { randomString() } rMessage by lazy { randomString() } Message by lazy { randomString() } rMessage by lazy { randomString() } ckk<Trace>() } { ce(any()) } returns trace (any(), any()) } just Runs (trace) } just Runs /** * Generates a random string in the form of a [UUID]. */ fun randomString() = UUID.randomUUID().toString()

167.

@Test fun ìnitial state should have loginSuccessful set to false`()
{ viewStateAssertion.assertFirstViewState { assertThat(it.loginSuccessful).isFalse() } } @Test fun ìnitial state should have loginEnabled set to false`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginEnabled).isFalse() } } @Test fun ìnitial state should have loginForm set to empty values`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginForm).isEqualTo(LoginViewModel.LoginForm()) } }

168.

@Test fun ìnitial state should have loginSuccessful set to false`()
{ viewStateAssertion.assertFirstViewState { assertThat(it.loginSuccessful).isFalse() } } @Test fun ìnitial state should have loginEnabled set to false`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginEnabled).isFalse() } } @Test fun ìnitial state should have loginForm set to empty values`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginForm).isEqualTo(LoginViewModel.LoginForm()) } }

169.

statefulModel.state.removeObserver(currentObserver!!) } currentObserver = null } fun assertLastViewState(assertion: (actualState: S)
-> Unit) { assertViewStateSeries { actualStates -> assertion(actualStates.last()) } } fun assertFirstViewState(assertion: (actualState: S) -> Unit) { assertViewStateSeries { actualStates -> assertion(actualStates.first()) } } fun assertViewStateSeries(assertion: (actualStates: List<S>) -> Unit) { assertion(viewStates) } }

170.

statefulModel.state.removeObserver(currentObserver!!) } currentObserver = null } fun assertLastViewState(assertion: (actualState: S)
-> Unit) { assertViewStateSeries { actualStates -> assertion(actualStates.last()) } } fun assertFirstViewState(assertion: (actualState: S) -> Unit) { assertViewStateSeries { actualStates -> assertion(actualStates.first()) } } fun assertViewStateSeries(assertion: (actualStates: List<S>) -> Unit) { assertion(viewStates) } }

171.

class ViewStateAssertion<S : ViewState> { private val viewStates = mutableListOf<S>()
private var currentObserver: Observer<S>? = null private lateinit var statefulModel: StatefulModel<S> val numberOfStates: Int get() = viewStates.size fun start(statefulModel: StatefulModel<S>) { this.statefulModel = statefulModel currentObserver = Observer { viewStates.add(it!!) } try { viewStates.clear() } catch (ex: Exception) { Assert.fail("Unable to complete ViewStateAssertion.start(). The followin } this.statefulModel.state.observeForever(currentObserver!!) }

172.

@Test fun `accountTextChanges should update the loginForm with new account
value`() { prepareForFormInteractions() accountTextChanges.updateValue(textChange) viewStateAssertion.assertLastViewState { assertThat(it.loginForm.account).isEqualTo(textChange) } } @Test fun `usernameTextChanges should update the loginForm with new username value`() { prepareForFormInteractions() usernameTextChanges.updateValue(textChange) viewStateAssertion.assertLastViewState { assertThat(it.loginForm.username).isEqualTo(textChange) } }

173.

} this.statefulModel.state.observeForever(currentObserver!!) } fun end() { if (currentObserver != null)
{ statefulModel.state.removeObserver(currentObserver!!) } currentObserver = null } fun assertLastViewState(assertion: (actualState: S) -> Unit) { assertViewStateSeries { actualStates -> assertion(actualStates.last()) } } fun assertFirstViewState(assertion: (actualState: S) -> Unit) { assertViewStateSeries { actualStates -> assertion(actualStates.first()) } }

174.

@Test fun `accountTextChanges should update the loginForm with new account
value`() { prepareForFormInteractions() accountTextChanges.updateValue(textChange) viewStateAssertion.assertLastViewState { assertThat(it.loginForm.account).isEqualTo(textChange) } } @Test fun `usernameTextChanges should update the loginForm with new username value`() { prepareForFormInteractions() usernameTextChanges.updateValue(textChange) viewStateAssertion.assertLastViewState { assertThat(it.loginForm.username).isEqualTo(textChange) } }

175.

Looking Ahead Kotlin is just getting started.

176.

Coroutines It’s like multi-threading without overhead and imperative.

177.

Contracts What if your functions could provide visibility into what
they infer internally?

178.

Inline Classes Give meaning to things like Strings and Ints
without overhead.

179.

Kotlin/Native Kotlin isn’t bound to the JVM.

180.

Questions? Let’s talk after or message me on engel.dev

Kotlin 2 ½ Years Later

Kotlin 2 ½ Years Later

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