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
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
Goodbye NPE if (nullDoesntExist != null) { } Kotlin greatly reduces the chance that you will inadvertently cause a NullPointerException in production. engel.dev
package kotlin public open class KotlinNullPointerException : java.lang.NullPointerException { public constructor() { /* compiled code */ } public constructor(message: kotlin.String?) { /* compiled code */ } } Because NPEs Still Exist.
val stringWithNothing: String? = null if (stringWithNothing != null) Which Do You Prefer? val stringWithNothing: String = “” stringWithNothing.isNotEmpty()
val possiblyNull: String? = null val definitelyNotNull = possiblyNull?.let { println("Cool this wasn't null.") } ?: { println("This used to be null.") "" }()
val possiblyNull: String? = null val definitelyNotNull = possiblyNull?.let { println("Cool this wasn't null.") } ?: { println("This used to be null.") "" }.invoke()
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 )
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 )
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 ) Required: String, Found String?
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 ) Required: String, Found String? Required: String, Found String?
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 ) Required: String, Found String? Required: String, Found String? Required: String, Found String?
// 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. }
} 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. }
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
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.
class Cat( val name: String = "Tina", val age: Int = 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.
class Cat( val name: String = "Tina", val age: Int = 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.
class Cat( val name: String = "Tina", val age: Int = 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.
class Cat( val name: String = "Tina", val age: Int = 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.
data class Cat( val name: String = "Tina", val age: Int = 4, currentlyHungry: Boolean ) " Exciting Data Class. Data class primary constructor must have only property (val/var) parameters
data class Cat( val name: String = "Tina", val age: Int = 4 ) val shouldBeTrue = tina.equals(Cat(name = “Tina")) val shouldBeConsistent = tina.hashCode() Using Data Classes.
data class Cat( val name: String = "Tina", val age: Int = 4 ) val tinaIsOlder = tina.copy(age = 5) val shouldBeTrue = tina.equals(Cat(name = “Tina")) val shouldBeConsistent = tina.hashCode() Using Data Classes.
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
sealed class DealCustomFieldValue( val fieldId: Long?, val value: String?, val title: String?, val order: Long?, val type: String?, val fieldValueId: Long? ) { data class StandardFieldValue(
) { 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,
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(
sealed class DealCustomFieldValue( val fieldId: Long?, val value: String?, val title: String?, val order: Long?, val type: String?, val fieldValueId: Long? ) { data class StandardFieldValue(
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?,
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?,
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()
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 ) } 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() }
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 ) } } }
when (this) { is DealCustomFieldValue.CurrencyFieldValue -> {} is DealCustomFieldValue.NumberFieldValue -> {} is DealCustomFieldValue.StandardFieldValue -> {} }
when (this) { is DealCustomFieldValue.CurrencyFieldValue -> {} is DealCustomFieldValue.NumberFieldValue -> {} is DealCustomFieldValue.StandardFieldValue -> {} else -> {} }
when (this) { is DealCustomFieldValue.CurrencyFieldValue -> {} is DealCustomFieldValue.NumberFieldValue -> {} is DealCustomFieldValue.StandardFieldValue -> {} else -> { /* not necessary */ } }
when (this) { is DealCustomFieldValue.CurrencyFieldValue -> {} is DealCustomFieldValue.NumberFieldValue -> { createStandardField( title = title ?: "", body = value.toDoubleFormatTwoDecimalPlaces(), leftIcon = R.drawable.ic_short_text ) } is DealCustomFieldValue.StandardFieldValue -> {} }
when (this) { is DealCustomFieldValue.CurrencyFieldValue -> {} 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 ) } }
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 ) }
Collections.kt val cats = listOf() 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
val cats = listOf() 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.
val cats = listOf() 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.
val cats = listOf() 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.
val cats = listOf() 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.
val cats = listOf() 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.
val cats = listOf() 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.
val cats = listOf() 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.
val cats = listOf() 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.
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.
// 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.
// Random Cat, from the last 20 elements, older than 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()
// Random Cat, from the last 20 elements, older than 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()
.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()
.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()
.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()
.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()
cats.reversed().asSequence() .take(20) .filter { it.age > 4 } .toList() .random() sealed class FieldValue { abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
abstract val value: T data class NumericField(override val value: Long) : FieldValue() data class MoneyField(override val value: Double) : FieldValue() data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues }
data class TextField(override val value: String) : FieldValue() data class MultiSelect(override val value: List) : FieldValue>() } val fieldValues = listOf() val fieldGroup = mutableMapOf>() for (fieldValue in fieldValues) { val fieldGroupValues = fieldGroup[fieldValue::class] ?: mutableListOf() fieldGroupValues.add(fieldValue) fieldGroup[fieldValue::class] = fieldGroupValues } val fieldValues = listOf() val fieldGroup = fieldValues.groupBy { it::class }
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
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
abstract class AbstractActivity : AppCompatActivity(), DisposableHandler by DisposableHandlerReal(), KeyboardHandler by KeyboardHandlerReal() { override fun addDisposable(disposable: Disposable) {} override fun addDisposables(vararg disposables: Disposable) {} override fun clearDisposables() {} }
abstract class AbstractActivity : AppCompatActivity(), DisposableHandler by DisposableHandlerReal(), KeyboardHandler by KeyboardHandlerReal() { override fun showKeyboard(context: Context) {} override fun dismissKeyboard(context: Context, view: View) {} }
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) }
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 $thisRef.") } } class Delegate { operator fun getValue(thisRef: Any?, property: KProperty<*>): String operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) }
val lazyInitialization by lazy { """ This String Is Created When First Needed Then Cached And Reused In The Future """.trimIndent() } operator fun getValue(thisRef: Any?, property: KProperty<*>): String { return "$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.") } }
""".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
* 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 lazy(initializer: () -> T): Lazy = 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.
*/ public actual fun lazy(lock: Any?, initializer: () -> T): Lazy = SynchronizedLazyImpl(initializer, lock) private class SynchronizedLazyImpl(initializer: () -> T, lock: Any? = null) : Lazy, 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) {
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
val startTime = System.currentTimeMillis() for (i in 0..100000) { println("Cat: ${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime
val startTime = System.currentTimeMillis() for (i in 0..100000) { println("Cat: ${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime
val startTime = System.currentTimeMillis() for (i in 0..100000) { println("Cat: ${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime
val startTime = System.currentTimeMillis() for (i in 0..100000) { println("Cat: ${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime
val startTime = System.currentTimeMillis() for (i in 0..100000) { println("Cat: ${Cat()}") } val endTime = System.currentTimeMillis() val runtime = endTime - startTime
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() }
abstract class ListViewModelAdapter> : RecyclerView.Adapter() { protected abstract val listViewModel: ListViewModel 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]) } }
abstract class ListViewModelAdapter> : RecyclerView.Adapter() { protected abstract val listViewModel: ListViewModel 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]) } }
abstract class ListViewModelAdapter> : RecyclerView.Adapter() { 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() } } }
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 = ViewStateAssertionprivate 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( 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
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() private val accountTextChanges by lazy { EventObservable() } private val usernameTextChanges by lazy { EventObservable() } private val passwordTextChanges by lazy { EventObservable() } private val domainTextChanges by lazy { EventObservable() } private val loginClicks by lazy { EventObservable() } 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() }
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() private val accountTextChanges by lazy { EventObservable() } private val usernameTextChanges by lazy { EventObservable() } private val passwordTextChanges by lazy { EventObservable() } private val domainTextChanges by lazy { EventObservable() } private val loginClicks by lazy { EventObservable() } 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() } MockKAnnotations.init(this)
private val viewStateAssertion = ViewStateAssertion() private val accountTextChanges by lazy { EventObservable() } private val usernameTextChanges by lazy { EventObservable() } private val passwordTextChanges by lazy { EventObservable() } private val domainTextChanges by lazy { EventObservable() } private val loginClicks by lazy { EventObservable() } 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() } private fun prepareTelemetry() { every { telemetry.startTrace(any()) } returns trace every { trace.putAttribute(any(), any()) } just Runs every { telemetry.endTrace(trace) } just Runs }
private val viewStateAssertion = ViewStateAssertion() private val accountTextChanges by lazy { EventObservable() } private val usernameTextChanges by lazy { EventObservable() } private val passwordTextChanges by lazy { EventObservable() } private val domainTextChanges by lazy { EventObservable() } private val loginClicks by lazy { EventObservable() } 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() } private fun prepareTelemetry() { every { telemetry.startTrace(any()) } returns trace every { trace.putAttribute(any(), any()) } just Runs every { telemetry.endTrace(trace) } just Runs }
private val viewStateAssertion = ViewStateAssertion() private val accountTextChanges by lazy { EventObservable() } private val usernameTextChanges by lazy { EventObservable() } private val passwordTextChanges by lazy { EventObservable() } private val domainTextChanges by lazy { EventObservable() } private val loginClicks by lazy { EventObservable() } 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() } private fun prepareTelemetry() { every { telemetry.startTrace(any()) } returns trace every { trace.putAttribute(any(), any()) } just Runs every { telemetry.endTrace(trace) } just Runs }
= ViewStateAssertion() by lazy { EventObservable() } s by lazy { EventObservable() } s by lazy { EventObservable() } by lazy { EventObservable() } y { EventObservable() } { randomString() } zy { randomString() } e by lazy { randomString() } rMessage by lazy { randomString() } Message by lazy { randomString() } rMessage by lazy { randomString() } ckk() } { 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()
@Test fun `initial state should have loginSuccessful set to false`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginSuccessful).isFalse() } } @Test fun `initial state should have loginEnabled set to false`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginEnabled).isFalse() } } @Test fun `initial state should have loginForm set to empty values`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginForm).isEqualTo(LoginViewModel.LoginForm()) } }
@Test fun `initial state should have loginSuccessful set to false`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginSuccessful).isFalse() } } @Test fun `initial state should have loginEnabled set to false`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginEnabled).isFalse() } } @Test fun `initial state should have loginForm set to empty values`() { viewStateAssertion.assertFirstViewState { assertThat(it.loginForm).isEqualTo(LoginViewModel.LoginForm()) } }
@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) } }
@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) } }
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