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How to Kotlinͷηογϣϯ͔ΒKotlinΒ͍͠දݱΛֶͿ
(from Google I/O 2018)
@sasamihoo
ू·ΕKotlin͖ʂKotlinѪձ vol1
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Target session
— How to Kotlin - from the Lead Kotlin Language
Designer (Google I/O '18)
— Andrey Breslav
— Live Coding
ू·ΕKotlin͖ʂKotlinѪձ vol1
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Profile
— @sasamihoo
— ใܥ(IoTܥ)ͷݚڀࣨ(M2)
— Androidྺ2͘Β͍
ू·ΕKotlin͖ʂKotlinѪձ vol1
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Overview
1. class
2. Property
3. DSLs
4. Expression
5. Lambdas
6. Coroutines
7. Lazy Sequence
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1-1: class
class Bean {
private var name: String
private var age: Int
constructor(n: String, a: Int) {
name = n
age = a
}
fun getName(): String {
return name
}
fun getAge(): Int {
return age
}
}
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1-1: class
class Bean(val name: String, val age: Int)
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1-2: class
fun parseName(name: String): List {
val space = name.indexOf(' ')
return listOf(
name.substring(0, space),
name.substring(space + 1)
)
}
fun main(args: Array) {
val name = parseName("Jane Doe")
val first = name.first[0]
val last = name.last[1]
println("$first $last")
if (name != parseName("Jane Doe")) {
println("!!!!!!!!!!!!!!!!!!!!!")
println("Equals does not work!!")
println("!!!!!!!!!!!!!!!!!!!!!")
}
}
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1-2: class
class FullName(val first: String, val last: String)
fun parseName(name: String): FullName {
val space = name.indexOf(' ')
return FullName(
name.substring(0, space),
name.substring(space + 1)
)
}
fun main(args: Array) {
val name = parseName("Jane Doe")
val first = name.first
val last = name.last
println("$first $last")
if (name != parseName("Jane Doe")) {
println("!!!!!!!!!!!!!!!!!!!!!")
println("Equals does not work!!")
println("!!!!!!!!!!!!!!!!!!!!!")
}
}
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1-2: class
data class FullName(val first: String, val last: String)
fun parseName(name: String): FullName {
val space = name.indexOf(' ')
return FullName(
name.substring(0, space),
name.substring(space + 1)
)
}
fun main(args: Array) {
val name = parseName("Jane Doe")
val first = name.first
val last = name.last
println("$first $last")
if (name != parseName("Jane Doe")) {
println("!!!!!!!!!!!!!!!!!!!!!")
println("Equals does not work!!")
println("!!!!!!!!!!!!!!!!!!!!!")
}
}
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2-1 Property
private var prop: String = "..."
fun getProp() = prop
fun setProp(v: String) {
println("New value: $v")
prop = v
}
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2-1 Property
custom setter
private var prop: String = "..."
set(v) {
println("New value: $v")
field = v
}
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2-2 Property
private var _os: String? = null
val os: String
get() {
if (_os == null) {
println("Computing")
_os = System.getProperty("os.name") +
" v" + System.getProperty("os.name") +
" (" + System.getProperty("os.arch") + ")"
}
return _os!!
}
fun main(args: Array) {
for (i in 1..3) {
println(os)
}
}
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2-2 Property
val os: String by lazy {
println("Computing")
System.getProperty("os.name") +
" v" + System.getProperty("os.name") +
" (" + System.getProperty("os.arch") + ")"
}
fun main(args: Array) {
for (i in 1..3) {
println(os)
}
}
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2-3 Property
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2-3 Property
import kotlin.properties.Delegates
var observeMe by Delegates.observable("a") { p, old, new ->
println("$${p.name} goes $old -> $new")
}
fun main(args: Array) {
println("\n\nObservable property:")
observeMe = "bb"
observeMe = "ccc"
observeMe = "dddd"
}
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2-4 Property
var p1: String = "initial"
get() {
println("You read me")
return field
}
set(v) {
println("You write me")
field = v
}
var p2: String = "initial"
get() {
println("You read me")
return field
}
set(v) {
println("You write me")
field = v
}
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2-4 Property
var p3 by Prop("initial")
var p4 by Prop("initial")
var p5 by Prop("initial")
class Prop(var field: String) {
operator fun getValue(thisRef: Any?, p: KProperty<*>): String {
println("You read me")
return field
}
operator fun setValue(thisRef: Any?, p: KProperty<*>, v: String) {
println("You write me")
field = v
}
}
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2-5 Property
class StringUtils {
fun getFirstWord(s: String, separator: String): String {
val index = s.indexOf(separator)
return if (index < 0) s else s.substring(0, index)
}
fun getFirstWord(s: String) = getFirstWord(s, "")
}
fun main(args: Array) {
println(
StringUtils().getFirstWord("Jane Doe")
)
}
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2-5 Property
object StringUtils {
fun getFirstWord(s: String, separator: String): String {
val index = s.indexOf(separator)
return if (index < 0) s else s.substring(0, index)
}
fun getFirstWord(s: String) = getFirstWord(s, "")
}
fun main(args: Array) {
println(
StringUtils.getFirstWord("Jane Doe")
)
}
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2-5 Property
fun getFirstWord(s: String, separator: String): String {
val index = s.indexOf(separator)
return if (index < 0) s else s.substring(0, index)
fun getFirstWord(s: String) = getFirstWord(s, "")
}
fun main(args: Array) {
println(
StringUtils.getFirstWord("Jane Doe")
)
}
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2-5 Property
fun getFirstWord(s: String, separator: String = " "): String {
val index = s.indexOf(separator)
return if (index < 0) s else s.substring(0, index)
}
fun main(args: Array) {
println(
getFirstWord("Jane Doe", separator = “, ”)
)
}
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2-5 Property
fun String.getFirstWord(separater: String = " "): String {
val index = indexOf(separater)
return if (index < 0) this else substring(0, index)
}
fun main(args: Array) {
println(
"Jane Doe".getFirstWord()
)
}
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2-5 Property
val String.firstWord: String
get() {
val index = indexOf(" ")
return if (index < 0) this else substring(0, index)
}
fun main(args: Array) {
println(
"Jane Doe".firstWord
)
}
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3-1 DSLs
fun main(args: Array) {
val root = Container(
Text("a"),
Container(
Text("b"),
Container(
Text("c"),
Text("d")
),
Text("e")
),
Text("f")
)
println(root)
}
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3-1 DSLs
abstract class Element
class Container(vararg val children: Element) : Element()
class Text(val text: String) : Element()
fun Element.extractText(): String {
return extractText(this, StringBuilder()).toString()
}
fun extractText(e: Element, sb: StringBuilder): StringBuilder {
if (e is Text) {
val text = e as Text
sb.append(text.text)
} else if (e is Container) {
val container = e as Container
for (child in container.children) {
extractText(child, sb)
}
} else error("Unrecognised element: $e")
return sb
}
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3-1 DSLs
fun Element.extractText(): String {
val sb = StringBuilder()
fun extractText(e: Element) {
if (e is Text) {
val text = e as Text
sb.append(text.text)
} else if (e is Container) {
val container = e as Container
for (child in container.children) {
extractText(child)
}
} else error("Unrecognised element: $e")
}
extractText(this)
return sb.toString()
}
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3-1 DSLs
fun Element.extractText(): String {
val sb = StringBuilder()
fun extractText(e: Element) {
if (e is Text) {
sb.append(e.text)
} else if (e is Container) {
for (child in e.children) {
extractText(child)
}
} else error("Unrecognised element: $e")
}
extractText(this)
return sb.toString()
}
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3-1 DSLs
fun Element.extractText(): String {
val sb = StringBuilder()
fun extractText(e: Element) {
if (e is Text) {
sb.append(e.text)
} else if (e is Container) {
e.children.forEach(::extractText)
} else error("Unrecognised element: $e")
}
extractText(this)
return sb.toString()
}
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3-1 DSLs
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3-2 DSLs
fun Element.extractText(): String {
val sb = StringBuilder()
fun extractText(e: Element) {
when (e) {
is Text -> sb.append(e.text)
is Container -> e.children.forEach(::extractText)
else -> error("Unrecognized element: $e")
}
}
extractText(this)
return sb.toString()
}
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3-2 DSLs
sealed class Element
class Container(vararg val children: Element) : Element()
class Text(val text: String) : Element()
fun Element.extractText(): String {
val sb = StringBuilder()
fun extractText(e: Element) {
when (e) {
is Text -> sb.append(e.text)
is Container -> e.children.forEach(::extractText)
}
}
extractText(this)
return sb.toString()
}
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4-1 expression
class Example(val a: Int, val b: String?, val c: Boolean)
fun main(args: Array) {
val ex = Example(1, null, true)
val a = ex.a
val b = ex.b
val c = ex.c
println("a = " + a + ", b = " + b + ", c = " + c)
}
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4-1 expression
val ex = Example(1, null, true)
with(ex) {
println("a = $a, b = $b, c = $c")
}
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4-2 expression
val map = HashMap()
map.put("k1", 1)
map.put("k2", 2)
map.put("k3", 3)
for (e in map.entries) {
val key = e.key
val value = e.value
println(key + " -> " + value)
}
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4-2 expression
val map = mapOf(
"k1" to 1,
"k2" to 2,
"k3" to 3
)
for ((key, value) in map.entries) {
println("$key -> $value")
}
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4-3 expression
val s: String
if (System.currentTimeMillis() % 2L == 0L) {
println("Yay!")
"Luck!"
} else {
"Not this time"
}
println(s)
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4-3 expression
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4-3 expression
val s: String = if (System.currentTimeMillis() % 2L == 0L) {
println("Yay!")
"Luck!"
} else {
"Not this time"
}
println(s)
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4-3 expression
val s = if (System.currentTimeMillis() % 2L == 0L) {
println("Yay!")
"Luck!"
} else {
"Not this time"
}
println(s)
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4-4 expression
fun test(e: Example): String {
when (e.a) {
1 -> return "Even"
3 -> return "Even"
5 -> return "Even"
2 -> return "Odd"
4 -> return "Odd"
6 -> return "Odd"
else -> "Too Big"
}
}
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4-4 expression
fun test(e: Example): String =
when (e.a) {
1, 3, 5 -> "Even"
in setOf(2, 4, 6) -> "Odd"
else -> "Too Big"
}
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4-5 expression
fun test2(str: String?): String? {
println(str?.length)
str?.forEach(::println)
if (str == null) return null
if (str == null) throw RuntimeException("Unexpected null!!")
if (str == null) error("Unexpected null")
return ""
}
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4-5 expression
fun test2(str: String?): String? {
println(str?.length)
str?.forEach(::println)
str ?: return null
if (str == null) return null
if (str == null) throw RuntimeException("Unexpected null!!")
if (str == null) error("Unexpected null")
return ""
}
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5-1 lambdas
fun main(args: Array) {
val numbers = (1..100).toList()
val list = mutableListOf()
for (it in numbers) {
if (it % 16 == 0) {
list.add("0x" + it.toString(16))
}
}
println(list)
}
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5-1 lambdas
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5-1 lambdas
fun main(args: Array) {
val numbers = (1..100).toList()
val list = numbers
.filter { it % 16 == 0 }
.map { "0x" + it.toString(16) }
println(list)
}
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5-2 lambdas
…
repeat(6) {
println(list)
}
}
inline fun repeat(times: Int, body: (Int) -> Unit) {
for (index in 0 until times) {
body(index)
}
}
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6-1 coroutines
class CallbackService(val name: String) {
class Response(val from: CallbackService, val message: String)
fun request(from: String, callback: (Response) -> Unit) {
//Do work...
callback(Response(this, "Hi $from!\n -- Yours, $name"))
}
}
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6-1 coroutines
fun main(args: Array){
val s1 = CallbackService("1")
val s2 = CallbackService("2")
s1.request(s2.name) { r1 ->
println(r1.message)
r1.from.request(s1.name) { r2 ->
println(r2.message)
}
}
}
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6-1 coroutines
fun CallbackService.sendMany(vararg from: String, callback: (CallbackService.Response) -> Unit) {
if (from.isEmpty()) return
this.request(from[0]) { r ->
callback(r)
sendMany(*from.copyOfRange(1, from.size), callback = callback)
}
}
…
s1.sendMany("a", "b", "c") { r ->
println(r.message)
}
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6-2 coroutines
runBlocking {
val r1 = s1.request(s2.name)
val r2 = s2.request(s1.name)
for (from in listOf("a", "b", "c")) {
println(s1.request(from).message)
}
}
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6-2 coroutines
suspend fun CallbackService.request(from: String) =
suspendCoroutine { cont ->
request(from) { r ->
//called after execution is finished
cont.resume(r)
}
}
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6-2 coroutines
suspend fun CallbackService.request(from: String) =
suspendCoroutine { cont ->
try {
request(from) { r ->
//called after execution is finished
cont.resume(r)
}
} catch (e: Throwable) {
cont.resumeWithException(e)
}
}
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7-1 lazy sequence
fun main(args: Array) {
val seq = buildSequence {
var a = 1
var b = 1
while (true) {
yield(a)
val tmp = a
a = b
b += tmp
}
}
println(
seq.take(20).toList()
)
}
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7-1 lazy sequence
fun main(args: Array) {
val seq = buildSequence {
var a = 1
var b = 1
yield(2)
while (true) {
yield(a)
val tmp = a
if (tmp > 10) continue
a = b
b += tmp
}
}
println(
seq.take(20).toList()
)
}
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LiveCodingͷॻ͖ى͜͠
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LiveCodingͷॻ͖ى͜͠
ू·ΕKotlin͖ʂKotlinѪձ vol1
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LiveCodingͷ·ͶΛͯ͠Έͯ
— ϖΞϓϩͬΆ͍͜ͱ͕Ͱ͖Δ(?)
— ࣮ࡍʹखΛಈ͔͢͜ͱͰཧղ͕ਂ·Δ
— ͬͺΓ͔͔࣌ؒΔ…(ࢿྉͱ߹Θͤͯ7࣌ؒ͘Β͍!)
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Thanks!
ू·ΕKotlin͖ʂKotlinѪձ vol1