Kotlin을 여행하는 히치하이커의 준비서

Kotlin/Everywhere Seoul 2019 에서 발표한 자료입니다.

Transcript

1. Kotlinਸ ৈ೯ೞח ൤஖ೞ੉ழ੄ ળ࠺ࢲ Pluu
2. Pluu Dev. উ֞ೞࣁਃ. pluuੑפ׮. Google Developers Expert for Android GDG Korea Android Organizer Developer
3. Pluu Dev. ࣁ࣌ਸ ా೧ࢲ ঳ਸ ࣻ ੓ח Ѫ - "by" ఃਕ٘ী ؀ೠ ੄޷ - Kotlinীࢲ ੽Ӕೞח Delegation - ׮द ೠߣ Delegation ୓௼ - ࢚ࣘী ؀ೠ ऀ਷ য়ܨ ҕਬ
4. Pluu Dev. "by" ܳ ݅աӝ ੹ ঌҊ оঠ ೡ ѐ֛
5. Pluu Dev. Field Accessor Property
6. Pluu Dev. Property Accessor Setter Getter Field Effective Java #15 ௿ېझ৬ ݯߡ੄ ੽Ӕ ӂೠਸ ୭ࣗചೞۄ
7. Pluu Dev. Property Accessor Setter Getter Field Effective Java #15 ௿ېझ৬ ݯߡ੄ ੽Ӕ ӂೠਸ ୭ࣗചೞۄ
8. Pluu Dev. "by" the way
9. Pluu Dev. val lazyValue: String by lazy { "Hello" }
10. Pluu Dev. val lazyValue: String by lazy { "Hello" }
11. Pluu Dev. ఃਕ٘۽ ࠄ "by" • Interface ҳഅਸ ׮ܲ ё୓ী ਤ੐ • Property੄ Accessor ҳഅਸ ׮ܲ ё୓ী ਤ੐ Reference : https://kotlinlang.org/docs/reference/keyword-reference.html
12. Pluu Dev. ఃਕ٘۽ ࠄ "by" • Interface ҳഅਸ ׮ܲ ё୓ী ਤ੐ • Property੄ Accessor ҳഅਸ ׮ܲ ё୓ী ਤ੐ Reference : https://kotlinlang.org/docs/reference/keyword-reference.html Interface ҳഅਸ ׮ܲ ё୓ী ਤ੐ Property੄ Accessor ҳഅਸ ׮ܲ ё୓ী ਤ੐
13. Pluu Dev. Hard/Soft Keyword val else = 5 // Hard Keyword println(else) val by = 10 // Soft Keyword println(by) Compile Error // 10 // Example fun testSo*Keyword(by: Int) { println(by) }
14. Pluu Dev.
15. Pluu Dev. Grammar Reference : https://kotlinlang.org/docs/reference/grammar.html
16. Pluu Dev. Kotlinীࢲ "by"ۆ? Delegationਸ ਤೠ ఃਕ٘. Photo : https://www.saba.com/blog/5-reasons-managers-need-to-delegate
17. Pluu Dev. Delegation
18. ਤ੐਷ ё୓о ਃ୒ਸ ׮ܲ ё୓۽ ੹׳ೞѢա ਤ੐ೞח ҳഅ ݫழפ્ੑפ׮. GoF੄ ٣੗ੋ ಁఢ Pluu Dev.
19. Prototypical Objects ੽Ӕ ߑध਷ ӝࠄ ૑धਸ ಴അೞҊ ѐ֛ਸ ز੸ਵ۽ ࣻ੿ೞח ؘ ੓য ݻ о૑ ੢੼੉ ੓णפ׮. ਤ੐਷ ੉ܳ ё୓ ૑ೱ ঱য۽ ҳഅೞӝਤೠ ݫழפ્ੑפ׮. Using Prototypical Objects to Implement Shared Behavior in Object Oriented Systems by Henry Lieberman Pluu Dev.
20. Pluu Dev. Delegation Pattern ࣗ೐౟ਝয ূ૑פয݂ীࢲ ਤ੐ ಁఢ਷ ё୓ ҳࢿীࢲ ࢚ࣘҗ زੌೠ ௏٘ ੤ࢎਊਸ ׳ࢿೡ ࣻ ੓ب۾ೞח ё୓ ૑ೱ ٣੗ੋ ಁఢ Reference : https://en.wikipedia.org/wiki/Delegation_pattern
21. Pluu Dev. by delegate receiving object
22. Pluu Dev. by delegate receiving object
23. Pluu Dev. Simple Delegation Pattern class Rectangle(val width: Int, val height: Int) { fun area() = width * height } class Window(val bounds: Rectangle) { // Delegation fun area() = bounds.area() } Reference : https://en.wikipedia.org/wiki/Delegation_pattern
24. Pluu Dev. Delegation in Kotlin
25. Pluu Dev. Properties Delegate class Example { var p: String by Delegate() } val/var <property name>: <Type> by <expression> Reference : https://kotlinlang.org/docs/reference/delegated-properties.html
26. Pluu Dev. Properties Delegate import kotlin.reflect.KProperty class Delegate { operator fun getValue(thisRef: Any?, property: KProperty<*>): String { // Property Get ੽Ӕद ഐ୹ } operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) { // Property Set ੽Ӕद ഐ୹ } } Reference : https://kotlinlang.org/docs/reference/delegated-properties.html Reference : https://kotlinlang.org/docs/reference/operator-overloading.html
27. Pluu Dev. Properties Delegate class Example { var p: String by Delegate() } val example = Example() println(example.p) example.p = “A” delegate.getValue ഐ୹ delegate.setValue ഐ୹
28. Pluu Dev. Lazy val lazyValue: String by lazy { "Hello" } fun main() { println(lazyValue) println(lazyValue) } property ഐ୹੹ө૑ Instance ࢤࢿਸ ૑ো Ӓ ੉റח நदػ Instanceী ੽Ӕ
29. Pluu Dev. Lazy val lazyValue: String by lazy { "Hello" } झۨ٘۽ࠗఠ উ੹? زदࢿ ೲਊ?
30. Pluu Dev. LazyThreadSafetyMode public actual fun <T> lazy( mode: LazyThreadSafetyMode, initializer: () -> T ): Lazy<T> = when (mode) { LazyThreadSafetyMode.SYNCHRONIZED -> SynchronizedLazyImpl(initializer) LazyThreadSafetyMode.PUBLICATION -> SafePublicationLazyImpl(initializer) LazyThreadSafetyMode.NONE -> UnsafeLazyImpl(initializer) } Reference : https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/jvm/src/kotlin/util/LazyJVM.kt#L33 public actual fun <T> lazy( initializer: () -> T ): Lazy<T> = SynchronizedLazyImpl(initializer)
31. Pluu Dev. Kotlin stdlibীࢲ੄ Delegate Interface interface ReadOnlyProperty<in R, out T> { operator fun getValue(thisRef: R, property: KProperty<*>): T } interface ReadWriteProperty<in R, T> { operator fun getValue(thisRef: R, property: KProperty<*>): T operator fun setValue(thisRef: R, property: KProperty<*>, value: T) } Reference : https://kotlinlang.org/docs/reference/delegated-properties.html#property-delegate-requirements
32. Pluu Dev. Delegates.vetoable public inline fun <T> vetoable( initialValue: T, crossinline onChange: ( property: KProperty<*>, oldValue: T, newValue: T ) -> Boolean): ReadWriteProperty<Any?, T> = object : ObservableProperty<T>(initialValue) { override fun beforeChange( property: KProperty<*>, oldValue: T, newValue: T ): Boolean = onChange(property, oldValue, newValue) }
33. Pluu Dev. Delegates.vetoable class User { var name: String by Delegates.vetoable("initialValue") { _, _, new -> new.length > 5 } } fun main() { val user = User() user.name = "first" user.name = "second" println(user.name) } initialValue
34. Pluu Dev. Delegates.vetoable class User { var name: String by Delegates.vetoable("initialValue") { _, _, new -> new.length > 5 } } fun main() { val user = User() user.name = "first" user.name = "second" println(user.name) } ч ߸҃ ৈࠗܳ ౸ױೞח ௒ߔ
35. Pluu Dev. Delegates.observable public inline fun <T> observable( initialValue: T, crossinline onChange: ( property: KProperty<*>, oldValue: T, newValue: T ) -> Unit ): ReadWriteProperty<Any?, T> = object : ObservableProperty<T>(initialValue) { override fun afterChange( property: KProperty<*>, oldValue: T, newValue: T ) = onChange(property, oldValue, newValue) }
36. Pluu Dev. Delegates.observable class User { var name: String by Delegates.observable("initialValue") { _, old, new -> println("$old -> $new") } } fun main() { val user = User() user.name = "first" user.name = "second" } Reference : https://kotlinlang.org/docs/reference/delegated-properties.html#observable initialValue
37. Pluu Dev. Delegates.observable class User { var name: String by Delegates.observable("initialValue") { _, old, new -> println("$old -> $new") } } fun main() { val user = User() user.name = "first" user.name = "second" } Reference : https://kotlinlang.org/docs/reference/delegated-properties.html#observable ч ߸҃ റ ഐ୹غח ௒ߔ
38. Pluu Dev. public abstract class ObservableProperty<T>( initialValue: T) : ReadWriteProperty<Any?, T> { private var value = initialValue protected open fun beforeChange( property: KProperty<*>, oldValue: T, newValue: T): Boolean = true protected open fun afterChange( property: KProperty<*>, oldValue: T, newValue: T): Unit {} ... } ObservableProperty
39. Pluu Dev. public abstract class ObservableProperty<T>( initialValue: T) : ReadWriteProperty<Any?, T> { private var value = initialValue protected open fun beforeChange( property: KProperty<*>, oldValue: T, newValue: T): Boolean = true protected open fun afterChange( property: KProperty<*>, oldValue: T, newValue: T): Unit {} ... } /** Delegates.vetoableীࢲ overrideೞח ೣࣻ */ ObservableProperty
40. Pluu Dev. public abstract class ObservableProperty<T>( initialValue: T) : ReadWriteProperty<Any?, T> { private var value = initialValue protected open fun beforeChange( property: KProperty<*>, oldValue: T, newValue: T): Boolean = true protected open fun afterChange( property: KProperty<*>, oldValue: T, newValue: T): Unit {} ... } /** Delegates.observableীࢲ overrideೞח ೣࣻ */ ObservableProperty
41. Pluu Dev. Class Delegation interface A { fun blabla() fun blabla2() } class AImpl : A { override fun blabla() { println("Hello delegation!") } override fun blabla2() { println("blabla2 delegation!") } } class B(a: A) : A by a ೙ਃೠ ࠗ࠙݅ ੤੿੄ class C(private val a: A) : A by a { override fun blabla() { println("Override method!") } } class D : A by AImpl()
42. Pluu Dev. Local Delegated Properties (Since 1.1) ૑৉߸ࣻ ࢤࢿਸ ૑ো୊ܻ fun example(computeFoo: () -> Foo) { val memoizedFoo by lazy(computeFoo) if (someCondition && memoizedFoo.isValid()) { memoizedFoo.doSomething() } } Reference : https://kotlinlang.org/docs/reference/delegated-properties.html#local-delegated-properties-since-11
43. Pluu Dev. Local Delegated Properties (Since 1.1) ૑৉߸ࣻ ࢤࢿਸ ૑ো୊ܻ fun testLocalDelegation() { val database by lazy { createDatabase() } val cache by lazy { createMemoryCache() } if (mustUseDatabase()) { database.use { ... } } else { cache.use { ... } } } Reference : https://blog.jetbrains.com/kotlin/2017/04/kotlin-1-1-is-also-for-android-developers/ ૑ো ୡӝച۽ db/cache ઺ ೞա ࢎਊ
44. Pluu Dev. Providing a delegate (Since 1.1) class SharedPreferencesProperty( private val key: String, private val defaultValue: String? ) : ReadWriteProperty<PreferencesModel, String?> { override fun getValue(thisRef: PreferencesModel, property: KProperty<*> ): String? { return thisRef.sharedPreferences.getString(key, defaultValue) } override fun setValue( thisRef: PreferencesModel, property: KProperty<*>, value: String? ) { thisRef.sharedPreferences.edit().putString(key, value).apply() } }
45. Pluu Dev. Providing a delegate (Since 1.1) class SharedPreferencesPropertyProvider( private val key: String? = null, private val defaultValue: String? = null ) { operator fun provideDelegate( thisRef: PreferencesModel, prop: KProperty<*> ): ReadWriteProperty<PreferencesModel, String?> { val propertyName = prop.name val key = key ?: propertyName require(key.isNotEmpty()) { "Key cannot be empty" } return SharedPreferencesProperty(key, defaultValue) } }
46. Pluu Dev. Providing a delegate (Since 1.1) open class PreferencesModel(context: Context, name: String) { internal val sharedPreferences: SharedPreferences = context.getSharedPreferences(name, Context.MODE_PRIVATE) protected fun stringPreferences( key: String? = null, defaultValue: String? = null ) = SharedPreferencesPropertyProvider(key, defaultValue) }
47. Pluu Dev. Providing a delegate (Since 1.1) open class PreferencesModel(context: Context, name: String) { internal val sharedPreferences: SharedPreferences = context.getSharedPreferences(name, Context.MODE_PRIVATE) protected fun stringPreferences( key: String? = null, defaultValue: String? = null ) = SharedPreferencesPropertyProvider(key, defaultValue) } class UserPreferences( context: Context ) : PreferencesModel(context, "user") { var name: String? by stringPreferences() var profile: String? by stringPreferences("profile") }
48. Pluu Dev. Providing a delegate (Since 1.1) PreferencesModel # stringPreferences(key: String?, defaultValue: String?)
 : SharedPreferencesPropertyProvider UserPreferences + name: String? by stringPreferences + profile: String? by stringPreferences Providing a delegate (Since 1.1) SharedPreferencesPropertyProvider - key: String? - val defaultValue: String? + provideDelegate(thisRef: PreferencesModel, prop: KProperty<*>)
 : ReadWriteProperty<PreferencesModel, String?> SharedPreferencesProperty - key: String? - val defaultValue: String? + getValue(thisRef: PreferencesModel, property: KProperty<*>): String? + setValue(thisRef: PreferencesModel, property: KProperty<*>, value: String?)
49. Pluu Dev. androidীࢲ Delegation ഝਊ
50. Pluu Dev. bind/extra ৘द fun Activity.bindString(@StringRes resId: Int): Lazy<String> = lazy { getString(resId) } fun Activity.bindColor(@ColorRes resId: Int): Lazy<Int> = lazy { ContextCompat.getColor(this, resId) } fun <T : Parcelable> Activity.extra(key: String): Lazy<T> = lazy { intent.extras?.getParcelable<T>(key)!! } fun Activity.extraString(key: String): Lazy<String> = lazy { intent.getStringExtra(key) }
51. Pluu Dev. bind/extra ৘द fun Activity.bindString(@StringRes resId: Int): Lazy<String> = lazy { getString(resId) } fun Activity.bindColor(@ColorRes resId: Int): Lazy<Int> = lazy { ContextCompat.getColor(this, resId) } fun <T : Parcelable> Activity.extra(key: String): Lazy<T> = lazy { intent.extras?.getParcelable<T>(key)!! } fun Activity.extraString(key: String): Lazy<String> = lazy { intent.getStringExtra(key) } class TestActivity : Activity() { private val title by bindString(R.string.title) private val accentColor by bindColor(R.color.color_accent) private val param by extra<Param>(KEY_PARAM) private val keyword by extraString(KEY_KEYWORD) }
52. Pluu Dev. Preference ৘द class IntPreference( private val preferences: SharedPreferences, private val name: String, private val defaultValue: Int = 0 ) : ReadWriteProperty<Any, Int> { override fun getValue(thisRef: Any, property: KProperty<*>): Int { return preferences.getInt(name, defaultValue) } override fun setValue(thisRef: Any, property: KProperty<*>, value: Int) { preferences.edit().putInt(name, value).apply() } }
53. Pluu Dev. Preference ৘द class IntPreference( private val preferences: SharedPreferences, private val name: String, private val defaultValue: Int = 0 ) : ReadWriteProperty<Any, Int> { override fun getValue(thisRef: Any, property: KProperty<*>): Int { return preferences.getInt(name, defaultValue) } override fun setValue(thisRef: Any, property: KProperty<*>, value: Int) { preferences.edit().putInt(name, value).apply() } } class Test(private val pref: SharedPreferences) { val count: Int by IntPreference(pref, "count", 0) }
54. Pluu Dev. BaseObservable ഝਊ class UserModel(private val user: UserData) : BaseObservable() { @get:Bindable var name: String = "" get() = user.name set(value) { user.name = value notifyPropertyChanged(BR.name) } }
55. Pluu Dev. ObservablePropertyDelegate class ObservablePropertyDelegate<T> ( data: T, id: Int ) : ReadWriteProperty<Any?, T> { override fun getValue(thisRef: Any?, property: KProperty<*>): T { return data } override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) { data = value notifyPropertyChanged(id) } }
56. Pluu Dev. Delegation ੸ਊ ੹ class UserModel(private val user: UserData) : BaseObservable() { @get:Bindable var name: String = "" get() = user.name set(value) { user.name = value notifyPropertyChanged(BR.name) } }
57. Pluu Dev. Delegation ੸ਊ റ class UserModel(private val user: UserData) : BaseObservable() { @get:Bindable var name: String by ObservablePropertyDelegate(user.name, BR.name) }
58. Pluu Dev. findViewById ! WARNING
59. Pluu Dev. Puzzle Delegation
60. Pluu Dev. Quiz #1
61. Pluu Dev. fun mainTest() { val b = BaseImpl(100) b.printX() QuizType1(b, 30).printX() QuizType2(b, 30).printX() } interface Quiz1Base { val x: Int fun printX() { println(x) } } class BaseImpl( override val x: Int ) : Quiz1Base class QuizType1( b: Quiz1Base, override val x: Int ) : Quiz1Base by b class QuizType2( b: Quiz1Base, override val x: Int ) : Quiz1Base ? ? ?
62. Pluu Dev. interface Quiz1Base { val x: Int fun printX() { println(x) } } class BaseImpl( override val x: Int ) : Quiz1Base class QuizType1( b: Quiz1Base, override val x: Int ) : Quiz1Base by b class QuizType2( b: Quiz1Base, override val x: Int ) : Quiz1Base fun mainTest() { val b = BaseImpl(100) b.printX() QuizType1(b, 30).printX() QuizType2(b, 30).printX() } 100 100 30
63. Pluu Dev. fun mainTest() { val b = BaseImpl(100) b.printX() // 100 QuizType1(b, 30).printX() // 100 QuizType2(b, 30).printX() // 30 } QuizType1 (30) printX() QuizType2 (30) printX() <<interface>> Quiz1Base x: Int printX(): Unit BaseImpl (100) printX()
64. Pluu Dev. Quiz #2
65. Pluu Dev. class Quiz2HashSet<E> : HashSet<E>() { var addCount: Int = 0 private set override fun add( element: E ): Boolean { addCount++ return super.add(element) } override fun addAll( elements: Collection<E> ) : Boolean { addCount += elements.size return super.addAll(elements) } ... } val set = Quiz2HashSet<Int>() set.add(1) set.add(2) println(set.addCount) set.addAll(setOf(3, 4, 5)) println(set.addCount) ? ?
66. Pluu Dev. val set = Quiz2HashSet<Int>() set.add(1) set.add(2) println(set.addCount) set.addAll(setOf(3, 4, 5)) println(set.addCount) 2 8 class Quiz2HashSet<E> : HashSet<E>() { var addCount: Int = 0 private set override fun add( element: E ): Boolean { addCount++ return super.add(element) } override fun addAll( elements: Collection<E> ) : Boolean { addCount += elements.size return super.addAll(elements) } ... }
67. Pluu Dev. ݏ୶न ࠙ীѱ
68. Pluu Dev. • HashSet#addAll਷ AbstractCollection#addAllਸ ഐ୹ • addAll() ղࠗীࢲ addਸ ഐ୹ೣ java.lang.Object ⽸ java.util.AbstractCollection<E> ⽸ java.util.AbstractSet<E> ⽸ java.util.HashSet<E> class Quiz2HashSet<E> : HashSet<E>() { var addCount: Int = 0 private set override fun add( element: E ): Boolean { addCount++ return super.add(element) } override fun addAll( elements: Collection<E> ) : Boolean { addCount += elements.size return super.addAll(elements) } ... }
69. Pluu Dev. Inheritance addAllਸ ࢎਊೞݶ Countо য۵׮ ࠗݽ ௿ېझ੄ झಖী ੄ઓೞѱ ػ׮. …
70. Pluu Dev. Kotlin in Action 4.3.3 ௿ېझ ਤ੐: by ఃਕ٘ ࢎਊ Effective Java ই੉మ 18 ࢚ࣘࠁ׮ח ஹನ૑࣌ਸ ࢎਊೞۄ
71. Pluu Dev. class Quiz2HashSet<E> : HashSet<E>() { var addCount: Int = 0 private set override fun add(element: E): Boolean { addCount++ return super.add(element) } override fun addAll(elements: Collection<E>) : Boolean { addCount += elements.size return super.addAll(elements) } ... }
72. Pluu Dev. class Quiz2HashSet<E>( private val set: MutableSet<E> = mutableSetOf() ) : MutableSet<E> by set { var addCount: Int = 0 private set override fun add(element: E): Boolean { addCount++ return set.add(element) } override fun addAll(elements: Collection<E>): Boolean { addCount += elements.size return set.addAll(elements) } … } Class Delegation
 ਤ੐ ഋక۽ ҳഅ
73. Pluu Dev. Summary
74. Pluu Dev. Delegation ੢ױ੼ • ࢚ࣘ਷ ױ ೞա੄ Super Class݅ оמ,
 ਤ੐਷ ࠂࣻ Interface۽ оמ • بݫੋ ૑धਸ Delegationਵ۽ ऀӡ ࣻ ੓׮. • ࢚ࣘ਷ ё୓ ௼ӝо ૐоदఃח ࠺ਊ੉ ߊࢤ • Interface ੿੄о ೙ਃ • ਬোೞ૑݅ ੉೧ೞӝ য۵׮ • protected method/propertiesח ࢎਊ ࠛоמ
75. Pluu Dev. https://github.com/google/guava/blob/master/guava/src/com/google/common/collect/ForwardingCollection.java - Child Classח Super Class੄ ҳഅ ࣁࠗ ࢎ೦ী ੄ઓ
 ➤ ࢚ࣘ੉ ஭ङചܳ ӵ౟ܽ׮. [Snyder86] - ࢚ࣘ਷ ࠗݽ/੗ध੉ ࣽࣻೠ is-a ҙ҅ੌ ٸ ࢎਊ - ࢚ࣘ਷ API੄ ߧਤ৬ Ѿೣਸ ࢚ࣘؼ ࣻ ੓׮ - Decorator Pattern ਸ ੉ਊ೧ࢲ ҳഅী ૘઺ೞח ੽Ӕ
 ➤ Wrapper Class : Guava ForwardingCollection Effective Java #16 ࢚ࣘࠁ׮ח ஹನ૑࣌ਸ ࢎਊೞۄ
76. Pluu Dev. Reference • Kotlin Reference ~ Delegated Properties • [Blog] بହ਌ש੄ ನझ౟ ⭑⭑⭑⭑⭑ • https://medium.com/til-kotlin-ko/kotlin੄-௿ېझ-ਤ੐਷-যڌѱ-ز੘ೞחо- c14dcbbb08ad • https://medium.com/til-kotlin-ko/kotlin-delegated-property-by-lazyח-যڌѱ-ز ੘ೞחо-74912d3e9c56 • [Blog] Using Prototypical Objects to Implement Shared Behavior in Object Oriented Systems by Henry Lieberman • [Blog] Kotlin “By” Class Delegation: Favor Composition Over Inheritance • [Book] Effective Java • [Book] GoF ٣੗ੋ ಁఢ
77. Pluu Dev. END. Pluu pluulove@gmail.com http://pluu.github.io pluulove