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FORGOTTEN TRAITS
Михаил Розумянский
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ПРИМЕСЬ (MIXIN)
Subclass
Mixin
Base
Class
Mixin
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TRAIT
Отсутствие состояния
Ограничение базового класса
Переопределение методов базового класса
Вызов методов базового класса
Модификаторы доступа
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ОБЪЯВЛЕНИЕ
trait CollectionWithComparator> :
AbstractCollection {
protected val comparator: Comparator
override fun contains(element: E): Boolean {
return any { comparator.compare(it, element) == 0 }
}
}
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ИСПОЛЬЗОВАНИЕ
class CaseInsensitiveStringCollection :
AbstractCollection(),
CollectionWithComparator {
override val comparator = String.CASE_INSENSITIVE_ORDER
// ...
}
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ЧЕМ ЗАМЕНИТЬ?
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НИЧЕМ
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А НА САМОМ ДЕЛЕ?
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ЗАДАЧА
Manager Worker
Employee
delegates
implements
implements
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ДЕЛЕГАТ
Manager Worker
Employee
delegates
implements
implements
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СОТРУДНИК
interface Employee {
fun performTask(task: String)
}
abstract class AbstractEmployee(val name: String) : Employee {
fun say(text: String, vararg arguments: String) {
Output.write(name, text, *arguments)
}
}
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JAVA WAY
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WORKER
public class Worker extends AbstractEmployee {
public Worker(final String name) {
super(name);
}
@Override
public void performTask(final String task) {
say("I had to %s and I've just done it.", task);
}
}
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MANAGER
public class Manager extends AbstractEmployee {
private final Employee delegate = new Worker("Dilbert");
public Manager(final String name) { super(name); }
@Override
public void performTask(@NotNull final String task) {
delegate.performTask(task);
}
public void manageTask(@NotNull final String task) {
say("Hey, %s.", task);
performTask(task);
say("It's just a piece of cake to %s.", task);
}
}
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MAIN
public class Demo {
public static void main(final String[] args) {
final Manager manager = new Manager("Boss");
for (final String task : args) {
manager.manageTask(task);
}
}
}
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Boss
Hey, prepare a presentation.
Dilbert
I had to prepare a presentation and I've just done it.
Boss
It's just a piece of cake to prepare a presentation.
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KOTLIN WAY
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WORKER
class Worker(name: String) : AbstractEmployee(name) {
override fun performTask(task: String) {
say("I had to $task and I've just done it.")
}
}
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MANAGER
class Manager(
name: String
) : AbstractEmployee(name),
Employee by Worker("Dilbert") {
fun manageTask(task: String) {
say("Hey, $task.")
performTask(task)
say("It's just a piece of cake to $task.")
}
}
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ЧТО ВНУТРИ?
public final class Manager extends AbstractEmployee {
private final Worker $$delegate_0 = new Worker("Dilbert");
public Manager(@NotNull String name) { super(name); }
@Override public void performTask(@NotNull String task) {
$$delegate_0.performTask(task);
}
public final void manageTask(@NotNull String task) {
say("Hey, " + task + '.');
performTask(task);
say("It's just a piece of cake to " + task + '.');
}
}
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ДОСТУП К ДЕЛЕГАТУ
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НОВЫЙ MANAGER
class Manager private constructor(
name: String,
private val delegate: Employee
) : AbstractEmployee(name), Employee by delegate {
constructor(name: String) : this(name, Worker("Dilbert"))
override fun performTask(task: String) {
say("Hey, $task.")
delegate.performTask(task)
say("It's just a piece of cake to $task.")
}
}
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МОГЛО БЫ БЫТЬ И ЛУЧШЕ
— Distinguish syntactically when delegating
to a property
— Provide a way to reference a delegate
in class body
KT-83
KT-18427
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ИЗМЕНЕНИЕ ДЕЛЕГАТА
Manager Worker 1
Manager Worker 2
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НАИВНЫЙ ПОДХОД
private var delegate: Employee
fireAndHire()
private fun fireAndHire() {
say("Seems I need to fire this guy and hire someone else.")
delegate = Worker(Names.next())
}
class Manager private constructor(
name: String,
) : AbstractEmployee(name), Employee by delegate {
constructor(name: String) : this(name, Worker(Names.next()))
fun manageTask(task: String) {
say("Hey, $task.")
performTask(task)
say("It's just a piece of cake to $task.")
}
}
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Boss
Hey, prepare a presentation.
Dilbert
I had to prepare a presentation and I've just done it.
Boss
It's just a piece of cake to prepare a presentation.
Seems I need to fire this guy and hire someone else.
Hey, write a speech.
Dilbert
I had to write a speech and I've just done it.
Boss
It's just a piece of cake to write a speech.
Seems I need to fire this guy and hire someone else.
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НО ПОЧЕМУ?
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ДЕКОМПИЛИРУЕМ
private Employee delegate;
private final Employee $$delegate_0;
$$delegate_0 = delegate;
delegate = delegate;
$$delegate_0.performTask(task);
delegate = new Worker(Names.INSTANCE.next());
public final class Manager extends AbstractEmployee {
private Manager(String name, Employee delegate) {
super(name);
}
public Manager(@NotNull String name) {
this(name, new Worker(Names.INSTANCE.next());
}
public void performTask(@NotNull String task) {
}
private final void fireAndHire() {
say("Seems I need to fire this guy and hire someone else.");
}
}
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ОКАЗЫВАЕТСЯ
Для делегата всегда создаётся поле
— Delegation to var field
KT-5870
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И ЧТО ЖЕ ДЕЛАТЬ?
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ОЧЕРЕДНОЙ MANAGER
private var delegate = Worker(Names.next())
delegate.performTask(task)
delegate = Worker(Names.next())
class Manager(name: String) : AbstractEmployee(name) {
override fun performTask(task: String) {
say("Hey, $task.")
say("It's just a piece of cake to $task.")
fireAndHire()
}
private fun fireAndHire() {
say("Seems I need to fire this guy and hire someone else.")
}
}
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ПРЯМО КАК В JAVA
public class Manager extends AbstractEmployee {
private final Employee delegate = new Worker(Names.INSTANCE.next());
public Manager(final String name) { super(name); }
@Override public void performTask(task: String) {
say("Hey, %s.", task);
delegate.performTask(task);
say("It's just a piece of cake to %s.", task);
fireAndHire();
}
private void fireAndHire() {
say("Seems I need to fire this guy and hire someone else.");
delegate = Worker(Names.INSTANCE.next());
}
}
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ИНТЕРФЕЙСЫ С ЧАСТИЧНОЙ РЕАЛИЗАЦИЕЙ
interface DelegatingEmployee : Employee {
val delegate: Employee
override fun performTask(task: String) {
delegate.performTask(task)
}
}
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КАК РАБОТАЮТ?
public interface DelegatingEmployee extends Employee {
@NotNull Employee getDelegate();
void performTask(@NotNull String task);
final class DefaultImpls {
public static void performTask(
@NotNull DelegatingEmployee self,
@NotNull String task) {
self.getDelegate().performTask(task);
}
}
}
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ВТОРАЯ ПОПЫТКА
, DelegatingEmployee
override var delegate: Employee = Worker(Names.next())
super.performTask(task)
delegate = Worker(Names.next())
class Manager(name: String) : AbstractEmployee(name) {
override fun performTask(task: String) {
say("Hey, $task.")
say("It's just a piece of cake to $task.")
fireAndHire()
}
private fun fireAndHire() {
say("Seems I need to fire this guy and hire someone else.")
}
}
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Boss
Hey, prepare a presentation.
Dilbert
I had to prepare a presentation and I've just done it.
Boss
It's just a piece of cake to prepare a presentation.
Seems I need to fire this guy and hire someone else.
Hey, write a speech.
Wally
I had to write a speech and I've just done it.
Boss
It's just a piece of cake to write a speech.
Seems I need to fire this guy and hire someone else.
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ПРЯМО КАК В JAVA 8
public class Manager extends AbstractEmployee, DelegatingEmployee {
private final String name;
private Employee delegate = new Worker(Names.INSTANCE.next());
public Manager(final String name) { super(name); }
@Override public Employee getDeleagate() { return delegate; }
@Override public void performTask(final String task) {
say("Hey, %s.", task);
super.performTask(task);
say("It's just a piece of cake to %s.", task);
fireAndHire();
}
private void fireAndHire() {
say("Seems I need to fire this guy and hire someone else.");
delegate = Worker(Names.INSTANCE.next());
}
}
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ТОЛЬКО НЕМНОГО ХУЖЕ
— Generate default methods for
implementations in interfaces
— Introduce JvmDefault annotation
KT-4779
KT-19415
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ДЕЛЕГАТ ДЕЛЕГАТА
Manager Worker
Expert
implements uses
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ПОЯВЛЯЕТСЯ ЭКСПЕРТ
interface Expert {
fun answer(question: String)
}
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РАБОТНИК СПРАШИВАЕТ ЭКСПЕРТА
private val expert: Expert
ask("What is the theme?")
ask("When is the deadline?")
private fun ask(question: String) {
expert.answer(question)
}
class Worker(
name: String,
) : AbstractEmployee(name) {
override fun performTask(task: String) {
say("I had to $task and I've just done it.")
}
say(question)
}
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ОЧЕВИДНОЕ РЕШЕНИЕ
Employee by Worker("Dilbert", this),
Expert
override fun answer(question: String) {
say(MotivationalQuotes.random())
}
class Manager(
name: String
) : AbstractEmployee(name),
{
fun manageTask(task: String) {
say("Hey, $task.")
performTask(task)
say("It's just a piece of cake to $task.")
}
}
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НЕ РАБОТАЕТ
Error: 'this' is not defined in this context
— Allow passing this to a class delegate
KT-13603
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ИСПРАВЛЯЕМ
DelegatingEmployee
override val delegate: Employee = Worker("Dilbert", this)
class Manager(
name: String
) : AbstractEmployee(name), , Expert {
fun manageTask(task: String) {
say("Hey, $task.")
performTask(task)
say("It's just a piece of cake to $task.")
}
override fun answer(question: String) {
say(MotivationalQuotes.random())
}
}
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Boss
Hey, prepare a presentation.
Dilbert
What is the theme?
Boss
To win in the marketplace you must first win in the workplace.
Dilbert
When is the deadline?
Boss
If it scares you, it might be a good thing to try.
Dilbert
I had to prepare a presentation and I've just done it.
Boss
It's just a piece of cake to prepare a presentation.
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ОПЯТЬ КАК В JAVA 8
public class Manager extends AbstractEmployee implements DelegatingEmployee, Expert {
private final String name;
private final Employee delegate = new Worker("Dilbert", this);
public Manager(final String name) { super(name); }
public void manageTask(final String task) {
say("Hey, %s.", task);
performTask(task);
say("It's just a piece of cake to %s.", task);
}
@Override public Employee getDelegate() { return delegate; }
@Override public void answer(final String question) {
say(MotivationalQuotes.INSTANCE.random());
}
}
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В РЕЗУЛЬТАТЕ
Наличие состояния
Ограничение использования
Вызов методов контейнера
Модификаторы доступа
Отсутствие
базового класса
Переопределение методов базового класса
базового класса
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СПАСИБО ЗА ВНИМАНИЕ!
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