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KotlinとJavaとnullのライトな話
RyotaMurohoshi
November 26, 2016
Technology
2
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KotlinとJavaとnullのライトな話
2016/11/26(土)のKotlin Internal勉強会の資料です
#kotlin_internal
https://connpass.com/event/40360/
RyotaMurohoshi
November 26, 2016
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Transcript
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KotlinͱJavaͱnullͷϥΠτͳ @RyotaMurohoshi 2016/11/26()(Kotlin(internal(ษڧձ
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͜Μͳ͜ͱ͠·͢ • nullʹ·ͭΘΔKotlinݴޠ༷ͷ֬ೝ • όΠτίʔυͱσίϯύΠϧͨ͠JavaͲ͏ͳΔʁ • ͪΐͬͱ͚ͩίϯύΠϥͷίʔυݟΔ
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ࣗݾհ • ྄ࣨଠ(ΉΖ΄͠) • @RyotaMurohoshi • ࣄͰKotlin+Android • झຯͰC#+UnityͰήʔϜ։ൃ
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ͱ͜ΖͰɺ࠷ۙʹͨ͠هࣄͱ͔
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ʰnull$ͱϓϩάϥϛϯάݴޠʱ
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ʰnull͕;ΜͪΌ͔ʱ
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ʰnull͕͋Δϓϩάϥϛϯάݴޠ ͳΜͪΌΒʱ
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ۤ͠ΜͰΔ͔ΒΈΜͳnullͷ͖
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KotlinͷnullΛ͓͞Β͍
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String?Λฦؔ͢((Kotlinͷίʔυ) fun returnStringNullableKotlin(): String? = null
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͜ΕΛ͏ͱ!(Kotlinͷίʔυ) val str = returnNullableStringKotlin() // ͜ΕOK // val str
: String? = returnNullableStringKotlin() // ͜ΕίϯύΠϧΤϥʔ Type Mismatch // val str : String = returnNullableStringKotlin() // println(str.length) // ίϯύΠϧΤϥʔ println(str?.length) // ͜ΕͳΒOK
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͞Α͏ͳΒnullʂʂʂ
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ຊʹʁ
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ݱ࣮ͦΜͳʹ͘ͳ͍
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Kotlin͚ͩͰίʔυΛॻ͖͖ΕΔΘ͚Ͱͳ͍ ͦ͏ɺJavaͷίʔυΛݺͼग़͞ͳ͍ͱ͍͚ͳ͍ ͦͷ߹nullɺNullableʁ
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StringΛฦؔ͢'(Javaͷίʔυ) public class Utility { public static String returnNullableStringJava() {
return null; } }
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͜ΕΛ͏ͱ!(JavaͷίʔυΛKotlinͷίʔυ͔ΒݺͿ) val str = Utility.returnNullableStringJava() // ͜ΕOK // val str
: String? = Utility.returnNullableStringJava() // ʂʂʂ // ͜ΕOKʂʂ ʂ // val str : String = Utility.returnNullableStringJava()
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JavaͰॻ͍ͨStringΛฦ͢ϝιουͷฦΓɺ StringܕʹString?ܕʹೖͰ͖Δ StringͱString?ͬͯҧ͏ܕͩͬͨͣͳͷʹʁ
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ʲ࠶ܝʳ͜ΕΛ͏ͱ!(Kotlinͷίʔυ) val str = returnNullableStringKotlin() // ͜ΕOK // val str
: String? = returnNullableStringKotlin() // ͜ΕίϯύΠϧΤϥʔ Type Mismatch // val str : String = returnNullableStringKotlin() // println(str.length) // ίϯύΠϧΤϥʔ println(str?.length) // ͜ΕͳΒOK
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Pla$orm(Type U"lity.returnNullableStringJava()ͷฦΓPla6orm9Type
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• JavaͷࢀরܕͷϝιουͷฦΓͳͲɺPla'orm+Typeʹ • IDEͷ্ͰɺString!ͱ͔Person!ͱ͔ͬͯද͢ • ͚ͲίʔυͰɺString!ͱॻ͚ͳ͍
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ܕΛ໌ࣔతʹॻ͍ͨΒͲ͏ͳΔʁ
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U"lity.returnNullableStringJava()ͷฦΓ Stringܕʹೖͨ͠ΒҎޙɺStringܕͱͯ͠ѻ͏͠ String?ܕʹೖͨ͠ΒҎޙɺString?ܕͱͯ͠ѻ͏
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JavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ String?ʹೖ val str : String? = Utility.returnNullableStringJava() println(str?.length) //
ίϯύΠϧΤϥʔ // println(str.length)
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JavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ Stringʹೖ val str : String = Utility.returnNullableStringJava() println(str.length) //
ίϯύΠϧΤϥʔʮͰʯͳ͍͚Ͳ // ͦΕඞཁͳ͍Αͬͯɺܯࠂ͕ग़Δ // println(str?.length)
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JavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ ܕΛ໌ࣔ͠ͳ͍ͱ val str = Utility.returnNullableStringJava() // ͜ΕOK println(str?.length) //
͜ΕOKʁ(ίϯύΠϧΤϥʔʮͰʯͳ͍) println(str.length)
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ͳΔ΄ͲɺΊͰͨ͠ΊͰͨ͠ʁ
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ʹͳΒͳ͍ ղઆΛޙճ͠ʹ͕ͨ͠ʮ2ͭʯʂ
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ʲ࠶ܝʳStringΛฦؔ͢'(Javaͷίʔυ) public class Utility { public static String returnNullableStringJava() {
return null; } }
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͍ͭ͜nullฦͧ͢ʂ
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JavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ ܕΛ໌ࣔ͠ͳ͍ͱ val str = Utility.returnNullableStringJava() // ͜ΕOK println(str?.length) //
ίϯύΠϧΤϥʔͰͳ͍͚ΕͲɺ // ࣮ߦ࣌ʹʮjava.lang.NullPointerExceptionʯ println(str.length)
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͵ΔΆग़Δ͡ΌΜʂ Pla$orm(TypeͰɺʮNullPointerExcep5onʯͳ͛͏Δ
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͏ͻͱͭ
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ʲ࠶ܝʳJavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ Stringʹೖ val str : String = Utility.returnNullableStringJava() println(str.length) //
ίϯύΠϧΤϥʔʮͰʯͳ͍͚Ͳ // ͦΕඞཁͳ͍Αͬͯɺܯࠂ͕ग़Δ // println(str?.length)
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ͩΊͦ͏ U"lity.returnNullableStringJava()nullΛฦ͢ ͜ΕΛɺStringܕʹೖͯ͠ ී௨ʹϝϯόʹΞΫηεͯ͠͠·͍ͬͯΔ
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ɺͲ͏ͳΔʁ • ϝϯόʹΞΫηεͨ͠λΠϛϯάͰNullPointerExcep0on • ͦΕҎ֎ʢԿ͔ͷλΠϛϯάͰͳΜ͔ͷྫ֎Λ͛Δʣ
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ਖ਼ղɺʰͦΕҎ֎ʱ ϝϯόʹΞΫηε͢Δલʹྫ֎Λ͛Δ
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ʲ࠶ܝʳJavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ Stringʹೖ val str : String = Utility.returnNullableStringJava() println(str.length) //
ίϯύΠϧΤϥʔʮͰʯͳ͍͚Ͳ ͜ͷίʔυΛ࣮ߦ͢Δͱ...
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java.lang.IllegalStateExcep0on Λ͛Δ U"lity.returnNullableStringJava()5must5not5be5null
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NullPointerExcep/onͰͳͯ͘IllegalStateExcep/on ͱ͍͏͜ͱɺίϯύΠϥ͕Կ͔͍ͯ͠Δͣʂ ݟͯΈΑ͏
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ʲ࠶ܝʳJavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ Stringʹೖ val str : String = Utility.returnNullableStringJava() println(str.length) //
ίϯύΠϧΤϥʔʮͰʯͳ͍͚Ͳ ͜ͷByte%CodeΛΈͯΈΔ IDEAͰɺTools)>)Kotlin)>)Show)Kotlin)Bytecode
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L0 LINENUMBER 73 L0 INVOKESTATIC com/muhron/kotlin_java_interpolator/Utility.returnNullableStringJava ()Ljava/lang/String; DUP LDC "Utility.returnNullableStringJava()"
INVOKESTATIC kotlin/jvm/internal/Intrinsics.checkExpressionValueIsNotNull (Ljava/lang/Object;Ljava/lang/String;)V ASTORE 0 L1 LINENUMBER 74 L1 ALOAD 0 INVOKEVIRTUAL java/lang/String.length ()I ISTORE 1 NOP L2 GETSTATIC java/lang/System.out : Ljava/io/PrintStream; ILOAD 1 INVOKEVIRTUAL java/io/PrintStream.println (I)V L3 ͜ΕΛ͞ΒʹDecompoleʂ
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KotlinΛBytecodeʹͯ͠ɺͦΕΛ͞ΒʹDecompile String var10000 = Utility.returnNullableStringJava(); Intrinsics.checkExpressionValueIsNotNull(var10000, "Utility.returnNullableStringJava()"); String str =
var10000; int var1 = str.length(); System.out.println(var1);
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ϙΠϯτ ʮIntrinsics.checkExpressionValueIsNotNullʯ ϝϯόʹΞΫηε͢Δલʹɺ͜Ε͕ݺΕ͍ͯΔʂ
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ίʔυΛݟͯΈ·͠ΐ͏ʂ Intrinsics.checkExpressionValueIsNotNull
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h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/core/run;me.jvm/src/kotlin/jvm/internal/ Intrinsics.java#L86 package kotlin.jvm.internal; @SuppressWarnings("unused") public class Intrinsics {
private Intrinsics() { } /*ུ*/ public static void checkExpressionValueIsNotNull(Object value, String expression) { if (value == null) { throw sanitizeStackTrace(new IllegalStateException(expression + " must not be null")); } } /*ུ*/ }
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ͳΔ΄Ͳɺ͔֬ʹnullͩͬͨΒIllegalStateExcep.on͍͛ͯΔ
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Ͱɺ͜Ε୭͕Αͼ͍ͩͯ͠Δͷ͔ʁ ʮcheckExpressionValueIsNotNullʯͰ୳͢
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h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/compiler/backend/src/org/jetbrains/kotlin/codegen/ AsmU?l.java#L650 AsmU%lͱ͍͏தͰݺͼग़͍ͯ͠Δʂʂʂ ͞ΒʹಡΈਐΊΔͱ
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ExpressionCodegen#genQualified h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/compiler/backend/src/org/jetbrains/kotlin/codegen/ ExpressionCodegen.java#L291 ͱ Func%onCodegen#genDelegate h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/compiler/backend/src/org/jetbrains/kotlin/codegen/ Func>onCodegen.java#L1029
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ͳΔ΄Ͳ
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ͯ͞ɺKotlinͰίʔυΛॻ͚Δͱݴͬͯ Javaͱͷ૬ޓӡ༻ඞਢʂ nullͱͷઓ͍ͭͮ͘ͷͰ͋ͬͨ
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͚ͲͳΜͱ͔͍ͨ͠
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@NotNull ͱ @Nullable
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@NotNull
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Javaͷίʔυ // ΞϊςʔγϣϯΛ͚ͭΔ @NotNull public static String returnStringWithNotNullAnnotation() { return
""; }
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@NotNullͳJavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ // IDEɺฦΓܕ͕Stringͬͯڭ͑ͯ͘ΕΔʢString!Ͱͳ͍ʣ val str = Utility.returnStringWithNotNullAnnotation() // ͜ΕOK //
val str : String = Utility.returnStringWithNotNullAnnotation() // ࣮ɺ͜ΕOK //val str : String? = Utility.returnStringWithNotNullAnnotation() println(str?.length) // ܯࠂ͕ͰΔ println(str.length) // ͜ΕOK
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@NotNullͳJavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ Bytecode()>(JavaͰίϯύΠϧ String str = Utility.returnStringWithNotNullAnnotation(); int var1 = str.length();
System.out.println(var1);
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@Nullable
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Javaͷίʔυ // ΞϊςʔγϣϯΛ͚ͭΔ @Nullable public static String returnStringWithNullableAnnotation() { return
""; }
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@NullableͳJavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ // IDEɺฦΓܕ͕String?ͬͯڭ͑ͯ͘ΕΔʢString!Ͱͳ͍ʣ val str = Utility.returnStringWithNullableAnnotation() // ͜ΕOK //val
str : String? = Utility.returnNullableStringJava() // ͜ΕίϯύΠϧΤϥʔ //val str : String = Utility.returnStringWithNullableAnnotation() println(str?.length) // ͜ΕOK // println(str.length) // ͜ΕίϯύΠϧΤϥʔ
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@NullableͳJavaͷίʔυΛKotlinͷίʔυ͔ΒݺΜͰ Bytecode()>(JavaͰίϯύΠϧ String str = Utility.returnStringWithNullableAnnotation(); Integer var1 = str
!= null?Integer.valueOf(str.length()):null; System.out.println(var1);
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૬ޓӡ༻લఏͷJavaͷίʔυʹɺ @Nullabeͱ@NotNullΛ͚ͭΑ͏
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Androiderͷํɺ @Nullabeͱ͍͑ʁ
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LombokϢʔβʔͷํɺ @Nullableͱ͍͑ʁ
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FindbugsϢʔβʔͷํɺ @Nullableͱ͍͑ʁ
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JetBrainsతʹ @Nullabeͱ͍͑ʁ
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@NullableΊͬͪΌ͋Δʂʂʂ ͲͷNullableͩΑʂʁ
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࣮ෳରԠ͍ͯ͠Δ • org.jetbrains.annota.ons.Nullable • android.support.annota.on.Nullable • com.android.annota.ons.Nullable • org.eclipse.jdt.annota.on.Nullable •
org.checkerframework.checker.nullness.qual.Nullable h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/ java/JvmAnnota?onNames.kt
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࣮ෳରԠ͍ͯ͠Δʢଓ͖ʣ • javax.annota*on.Nullable • javax.annota*on.CheckForNull • edu.umd.cs.findbugs.annota*ons.CheckForNull • edu.umd.cs.findbugs.annota*ons.Nullable •
edu.umd.cs.findbugs.annota*ons.PossiblyNull h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/ java/JvmAnnota?onNames.kt
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͜͜ΒΜOK
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ίʔυΛ͍·͠ΐ͏
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h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/ java/JvmAnnota?onNames.kt val NULLABLE_ANNOTATIONS = listOf( JvmAnnotationNames.JETBRAINS_NULLABLE_ANNOTATION, FqName("android.support.annotation.Nullable"), FqName("com.android.annotations.Nullable"),
FqName("org.eclipse.jdt.annotation.Nullable"), FqName("org.checkerframework.checker.nullness.qual.Nullable"), FqName("javax.annotation.Nullable"), FqName("javax.annotation.CheckForNull"), FqName("edu.umd.cs.findbugs.annotations.CheckForNull"), FqName("edu.umd.cs.findbugs.annotations.Nullable"), FqName("edu.umd.cs.findbugs.annotations.PossiblyNull") )
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typeQualifiers.ktͷதʹ.... class JavaTypeQualifiers internal constructor( val nullability: NullabilityQualifier?, val mutability:
MutabilityQualifier?, internal val isNotNullTypeParameter: Boolean ) { companion object { val NONE = JavaTypeQualifiers(null, null, false) } } ͷnullabilityͷੜʹΘΕ͍ͯΔ h"ps:/ /github.com/JetBrains/kotlin/blob/1.0.5/core/descriptor.loader.java/src/org/jetbrains/kotlin/load/ java/typeEnhancement/typeQualifiers.kt#L42
75
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·ͱΊ • Pla%orm)TypeΛཧղ͠Α͏ • Javaͱͷ૬ޓӡ༻ՕॴͰɺNullPointetExcep8on IllegalStateExcep8onՄೳੑ͋Γ • JavaͷϥΠϒϥϦʹɺ@Nullableͱ@NotNull͚ͭΑ͏
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NextΞΫγϣϯ ίϯύΠϥɺJavaTypeQualifiersΛ༻͍ͯ AsmU%l͕Intrinsicsݺͼग़͢ίʔυΛు͍͍ͯΔ ͱࢥΘΕΔͷͰɺௐࠪ
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͋Γ͕ͱ͏͍͟͝·ͨ͠
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ؔ࿈ɾࢀߟ • Calling(Java(code(from(Kotlin h5ps:/ /kotlinlang.org/docs/reference/java=interop.html • Kotlin(M9ͰՃ͞ΕͨPlaAorm(Typeͷ h5p:/ /taro.hatenablog.jp/entry/2014/10/16/233702 •
ʲίʔυϦʔσΟϯάʳKotlin(to(JavaScriptίϯύΠϥϝϞ h5p:/ /yyyank.blogspot.jp/2015/05/kotlinkotlin=to= javascript.html
RyotaMurohoshi
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