20190211のKotlinに関する記事は6件です。

投稿日：2019-02-11T16:51:18+09:00

Kotlinのforループで独自クラスをイテレートする方法

概要

Kotlinでは、規約に従った実装を行うことで言語の構文に独自のプログラムを柔軟に組み込むことができます。
この記事では、 rangeTo の規約によって、forループ内で独自クラスをいてレートする実装例をご紹介します。

rangeTo と ClosedRange

Kotlin の for文は以下のように記述されますが、以下の 1..3 の部分の正体は ClosedRange です。
for (i in 1..3) print("${i*i} ") // 1 4 9
Kotlinのコンパイラは start..end を start.rangeTo(end) という呼び出しに変換するので、 start の型に rangeTo 関数が適切に定義されていれば、独自のクラスを for文の中でイテレートすることができます。
適切な、とは以下のシグネチャーで、 ClosedRange を返却する関数です。
operator fun <T: Comparable<T>> T.rangeTo(that: T): ClosedRange<T>
実装例

以下の十二支を表す列挙型(ChineseZodiac)をfor文で使えるように実装します。
enum class ChineseZodiac(val char: String) {
 RAT("子"), OX("丑"), TIGER("寅"), RABBIT("卯"), DRAGON("辰"), SNAKE("巳"),
 HORSE("午"), SHEEP("未"), MONKEY("申"), COCK("酉"), DOG("戌"), BOAR("亥"); 
}
まずは、実装コードの見通しをよくするために、12を法とした加算が行えるように以下の拡張関数を定義しておきます。
operator fun ChineseZodiac.plus(i: Int): ChineseZodiac {
 val ord = (this.ordinal + i) % 12
 return ChineseZodiac.values()[ord]
}
これも、規約に従った実装となっていて、 plus 関数を ChineseZodiac に追加することにより、+ による演算が可能となります。
println(RAT + 1) // OX
次に rangeTo を拡張関数として定義します。
operator fun ChineseZodiac.rangeTo(that: ChineseZodiac) = ChineseZodiacRange(this, that)
ChineseZodiacRange の定義は以下となります。
ChineseZodiac を型パラメータとして、 ClosedRange インタフェースを実装します。
class ChineseZodiacRange(override val start: ChineseZodiac,
 override val endInclusive: ChineseZodiac): ClosedRange<ChineseZodiac>
forループで in演算子によって ClosedRange をイテレートするためには、実はもう一つ規約に沿う必要があります。それは iterator() メソッドで Iterator を返却することです。
ChineseZodiacRangeの拡張関数として以下のように実装します。
operator fun ChineseZodiacRange.iterator(): Iterator<ChineseZodiac> =
 object : Iterator<ChineseZodiac> {
 private var current = start
 override fun hasNext() = current != (endInclusive + 1)
 override fun next(): ChineseZodiac {
 val ret = current
 current = current + 1
 return ret
 }
 }
これで、以下のようにforループでイテレートできるようになりました。
 for (e in TIGER..DRAGON) print(e.char) // 寅卯辰
 println()
 for (e in COCK..OX) print(e.char) // 酉戌亥子丑
 println()
 for (e in OX..OX) print(e.char) // 丑
 println()
ソースコード

今回の実装例のコード一式です：
import ChineseZodiac.*

fun main(args: Array<String>) {
 for (e in TIGER..DRAGON) print(e.char) // 寅卯辰
 println()
 for (e in COCK..OX) print(e.char) // 酉戌亥子丑
 println()
 for (e in OX..OX) print(e.char) // 丑
 println()
}

enum class ChineseZodiac(val char: String) {
 RAT("子"), OX("丑"), TIGER("寅"), RABBIT("卯"), DRAGON("辰"), SNAKE("巳"),
 HORSE("午"), SHEEP("未"), MONKEY("申"), COCK("酉"), DOG("戌"), BOAR("亥"); 
}

operator fun ChineseZodiac.plus(i: Int): ChineseZodiac {
 val ord = (this.ordinal + i) % 12
 return ChineseZodiac.values()[ord]
}

operator fun ChineseZodiac.rangeTo(that: ChineseZodiac) = ChineseZodiacRange(this, that)

class ChineseZodiacRange(override val start: ChineseZodiac,
 override val endInclusive: ChineseZodiac): ClosedRange<ChineseZodiac>

operator fun ChineseZodiacRange.iterator(): Iterator<ChineseZodiac> =
 object : Iterator<ChineseZodiac> {
 private var current = start
 override fun hasNext() = current != (endInclusive + 1)
 override fun next(): ChineseZodiac {
 val ret = current
 current = current + 1
 return ret
 }
 }

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投稿日：2019-02-11T16:30:00+09:00

各言語で定義できる関数のパラメータの最大個数

ちょっと気になって、関数で定義できるパラメータの最大個数について実験してみました。

255を閾値として、それ以上のパラメータを持つ関数を定義・実行できるのか、各言語のREPLを使って調べました。 (JavaScript はブラウザのコンソールです。)

JavaScript は256以上できたので "(unlimited)" としています、実際はもっと少ないかも。
C, C++, C# はある方からいただいたコメントを元にしています。
C, C++, NodeJS, PHP, Ruby について @Nabetani 様よりいただいた情報を反映しています。

Language	Version	the maximum number	note
C		127以上	コンパイラによって変わる。オーバフローが発生するまで制限なく扱える場合もある。 SOLOLEARN, @Nabetani
C++		256以上	コンパイラによって変わる。オーバフローが発生するまで制限なく扱える場合もある。 SOLOLEARN, @Nabetani
C#		16383	オーバフローするまで成功すると思われる。 Stackoverflow
Python	3.6.5	255	256個以上のパラメータを持つ関数は定義不可。
PHP	7.2.9	262145	オーバフローするまで成功すると思われる。 @Nabetani
Ruby	2.5.1	130767	オーバフローするまで成功すると思われる。 @Nabetani
Kotlin	1.3.0	255	256個以上のパラメータを持つ関数は定義可能だが実行時に `java.lang.NullPointerException` が発生する。
Java	11.0.2	255	256個以上のパラメータを持つ関数は定義不可。
JavaScript	Chrome 72.0.3626.96	(unlimited)	オーバフローするまで成功すると思われる。
NodeJS	11.9.0	65535	ルール上は65535。現実にはオーバフローするまで。 @Nabetani

特に Kotlin は 1.3 で 255個のパラメータを持つ関数を定義できるようになりました。 Java も、ルールとして 255までパラメータ持てることになっています。たぶん Scala も？

Python

シンタックスエラーが関数定義の時に255までしか受け付けませんとメッセージを返します。

>>> def f(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, a31, a32, a33, a34, a35, a36, a37, a38, a39, a40, a41, a42, a43, a44, a45, a46, a47, a48, a49, a50, a51, a52, a53, a54, a55, a56, a57, a58, a59, a60, a61, a62, a63, a64, a65, a66, a67, a68, a69, a70, a71, a72, a73, a74, a75, a76, a77, a78, a79, a80, a81, a82, a83, a84, a85, a86, a87, a88, a89, a90, a91, a92, a93, a94, a95, a96, a97, a98, a99, a100, a101, a102, a103, a104, a105, a106, a107, a108, a109, a110, a111, a112, a113, a114, a115, a116, a117, a118, a119, a120, a121, a122, a123, a124, a125, a126, a127, a128, a129, a130, a131, a132, a133, a134, a135, a136, a137, a138, a139, a140, a141, a142, a143, a144, a145, a146, a147, a148, a149, a150, a151, a152, a153, a154, a155, a156, a157, a158, a159, a160, a161, a162, a163, a164, a165, a166, a167, a168, a169, a170, a171, a172, a173, a174, a175, a176, a177, a178, a179, a180, a181, a182, a183, a184, a185, a186, a187, a188, a189, a190, a191, a192, a193, a194, a195, a196, a197, a198, a199, a200, a201, a202, a203, a204, a205, a206, a207, a208, a209, a210, a211, a212, a213, a214, a215, a216, a217, a218, a219, a220, a221, a222, a223, a224, a225, a226, a227, a228, a229, a230, a231, a232, a233, a234, a235, a236, a237, a238, a239, a240, a241, a242, a243, a244, a245, a246, a247, a248, a249, a250, a251, a252, a253, a254, a255, a256, a257):
...     print(1)
... 
  File "<stdin>", line 1
SyntaxError: more than 255 arguments

PHP

256以上のパラメータでも定義・実行できます。

php > function f($a0, $a1, $a2, $a3, $a4, $a5, $a6, $a7, $a8, $a9, $a10, $a11, $a12, $a13, $a14, $a15, $a16, $a17, $a18, $a19, $a20, $a21, $a22, $a23, $a24, $a25, $a26, $a27, $a28, $a29, $a30, $a31, $a32, $a33, $a34, $a35, $a36, $a37, $a38, $a39, $a40, $a41, $a42, $a43, $a44, $a45, $a46, $a47, $a48, $a49, $a50, $a51, $a52, $a53, $a54, $a55, $a56, $a57, $a58, $a59, $a60, $a61, $a62, $a63, $a64, $a65, $a66, $a67, $a68, $a69, $a70, $a71, $a72, $a73, $a74, $a75, $a76, $a77, $a78, $a79, $a80, $a81, $a82, $a83, $a84, $a85, $a86, $a87, $a88, $a89, $a90, $a91, $a92, $a93, $a94, $a95, $a96, $a97, $a98, $a99, $a100, $a101, $a102, $a103, $a104, $a105, $a106, $a107, $a108, $a109, $a110, $a111, $a112, $a113, $a114, $a115, $a116, $a117, $a118, $a119, $a120, $a121, $a122, $a123, $a124, $a125, $a126, $a127, $a128, $a129, $a130, $a131, $a132, $a133, $a134, $a135, $a136, $a137, $a138, $a139, $a140, $a141, $a142, $a143, $a144, $a145, $a146, $a147, $a148, $a149, $a150, $a151, $a152, $a153, $a154, $a155, $a156, $a157, $a158, $a159, $a160, $a161, $a162, $a163, $a164, $a165, $a166, $a167, $a168, $a169, $a170, $a171, $a172, $a173, $a174, $a175, $a176, $a177, $a178, $a179, $a180, $a181, $a182, $a183, $a184, $a185, $a186, $a187, $a188, $a189, $a190, $a191, $a192, $a193, $a194, $a195, $a196, $a197, $a198, $a199, $a200, $a201, $a202, $a203, $a204, $a205, $a206, $a207, $a208, $a209, $a210, $a211, $a212, $a213, $a214, $a215, $a216, $a217, $a218, $a219, $a220, $a221, $a222, $a223, $a224, $a225, $a226, $a227, $a228, $a229, $a230, $a231, $a232, $a233, $a234, $a235, $a236, $a237, $a238, $a239, $a240, $a241, $a242, $a243, $a244, $a245, $a246, $a247, $a248, $a249, $a250, $a251, $a252, $a253, $a254, $a255, $a256,  $a257) { echo 1; }
php >
php > function f($a0 = 1, $a1 = 1, $a2 = 1, $a3 = 1, $a4 = 1, $a5 = 1, $a6 = 1, $a7 = 1, $a8 = 1, $a9 = 1, $a10 = 1, $a11 = 1, $a12 = 1, $a13 = 1, $a14 = 1, $a15 = 1, $a16 = 1, $a17 = 1, $a18 = 1, $a19 = 1, $a20 = 1, $a21 = 1, $a22 = 1, $a23 = 1, $a24 = 1, $a25 = 1, $a26 = 1, $a27 = 1, $a28 = 1, $a29 = 1, $a30 = 1, $a31 = 1, $a32 = 1, $a33 = 1, $a34 = 1, $a35 = 1, $a36 = 1, $a37 = 1, $a38 = 1, $a39 = 1, $a40 = 1, $a41 = 1, $a42 = 1, $a43 = 1, $a44 = 1, $a45 = 1, $a46 = 1, $a47 = 1, $a48 = 1, $a49 = 1, $a50 = 1, $a51 = 1, $a52 = 1, $a53 = 1, $a54 = 1, $a55 = 1, $a56 = 1, $a57 = 1, $a58 = 1, $a59 = 1, $a60 = 1, $a61 = 1, $a62 = 1, $a63 = 1, $a64 = 1, $a65 = 1, $a66 = 1, $a67 = 1, $a68 = 1, $a69 = 1, $a70 = 1, $a71 = 1, $a72 = 1, $a73 = 1, $a74 = 1, $a75 = 1, $a76 = 1, $a77 = 1, $a78 = 1, $a79 = 1, $a80 = 1, $a81 = 1, $a82 = 1, $a83 = 1, $a84 = 1, $a85 = 1, $a86 = 1, $a87 = 1, $a88 = 1, $a89 = 1, $a90 = 1, $a91 = 1, $a92 = 1, $a93 = 1, $a94 = 1, $a95 = 1, $a96 = 1, $a97 = 1, $a98 = 1, $a99 = 1, $a100 = 1, $a101 = 1, $a102 = 1, $a103 = 1, $a104 = 1, $a105 = 1, $a106 = 1, $a107 = 1, $a108 = 1, $a109 = 1, $a110 = 1, $a111 = 1, $a112 = 1, $a113 = 1, $a114 = 1, $a115 = 1, $a116 = 1, $a117 = 1, $a118 = 1, $a119 = 1, $a120 = 1, $a121 = 1, $a122 = 1, $a123 = 1, $a124 = 1, $a125 = 1, $a126 = 1, $a127 = 1, $a128 = 1, $a129 = 1, $a130 = 1, $a131 = 1, $a132 = 1, $a133 = 1, $a134 = 1, $a135 = 1, $a136 = 1, $a137 = 1, $a138 = 1, $a139 = 1, $a140 = 1, $a141 = 1, $a142 = 1, $a143 = 1, $a144 = 1, $a145 = 1, $a146 = 1, $a147 = 1, $a148 = 1, $a149 = 1, $a150 = 1, $a151 = 1, $a152 = 1, $a153 = 1, $a154 = 1, $a155 = 1, $a156 = 1, $a157 = 1, $a158 = 1, $a159 = 1, $a160 = 1, $a161 = 1, $a162 = 1, $a163 = 1, $a164 = 1, $a165 = 1, $a166 = 1, $a167 = 1, $a168 = 1, $a169 = 1, $a170 = 1, $a171 = 1, $a172 = 1, $a173 = 1, $a174 = 1, $a175 = 1, $a176 = 1, $a177 = 1, $a178 = 1, $a179 = 1, $a180 = 1, $a181 = 1, $a182 = 1, $a183 = 1, $a184 = 1, $a185 = 1, $a186 = 1, $a187 = 1, $a188 = 1, $a189 = 1, $a190 = 1, $a191 = 1, $a192 = 1, $a193 = 1, $a194 = 1, $a195 = 1, $a196 = 1, $a197 = 1, $a198 = 1, $a199 = 1, $a200 = 1, $a201 = 1, $a202 = 1, $a203 = 1, $a204 = 1, $a205 = 1, $a206 = 1, $a207 = 1, $a208 = 1, $a209 = 1, $a210 = 1, $a211 = 1, $a212 = 1, $a213 = 1, $a214 = 1, $a215 = 1, $a216 = 1, $a217 = 1, $a218 = 1, $a219 = 1, $a220 = 1, $a221 = 1, $a222 = 1, $a223 = 1, $a224 = 1, $a225 = 1, $a226 = 1, $a227 = 1, $a228 = 1, $a229 = 1, $a230 = 1, $a231 = 1, $a232 = 1, $a233 = 1, $a234 = 1, $a235 = 1, $a236 = 1, $a237 = 1, $a238 = 1, $a239 = 1, $a240 = 1, $a241 = 1, $a242 = 1, $a243 = 1, $a244 = 1, $a245 = 1, $a246 = 1, $a247 = 1, $a248 = 1, $a249 = 1, $a250 = 1, $a251 = 1, $a252 = 1, $a253 = 1, $a254 = 1, $a255 = 1,  $a256 = 1) { echo 1; }
php > f()
php > ;
1

Ruby

256以上のパラメータでも実行できます。

2.5.1 :004 > def f(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, a31, a32, a33, a34, a35, a36, a37, a38, a39, a40, a41, a42, a43, a44, a45, a46, a47, a48, a49, a50, a51, a52, a53, a54, a55, a56, a57, a58, a59, a60, a61, a62, a63, a64, a65, a66, a67, a68, a69, a70,
a71, a72, a73, a74, a75, a76, a77, a78, a79, a80, a81, a82, a83, a84, a85, a86, a87, a88, a89, a90, a91, a92, a93, a94, a95, a96, a97, a98, a99, a100, a101, a102, a103, a104, a105, a106, a107, a108, a109, a110, a111, a112, a113, a114, a115, a116, a117, a118, a119, a120, a121, a122, a123, a124, a125, a126, a127, a128, a129, a130, a131, a132, a133, a134, a135, a136, a137, a138, a139, a140, a141, a142, a143, a144, a145, a146, a147, a148, a149, a150, a151, a152, a153, a154, a155, a156, a157, a158, a159, a160, a161, a162, a163, a164, a165, a166, a167, a168, a169, a170, a171, a172, a173, a174, a175, a176, a177, a178, a179, a180, a181, a182, a183, a184, a185, a186, a187, a188, a189, a190, a191, a192, a193, a194, a195, a196, a197, a198, a199, a200, a201, a202, a203, a204, a205, a206, a207, a208, a209, a210, a211, a212, a213, a214, a215, a216, a217, a218, a219, a220, a221, a222, a223, a224, a225, a226, a227, a228, a229, a230, a231, a232, a233, a234, a235, a236, a237, a238, a239, a240, a241, a242, a243, a244, a245, a246, a247, a248, a249, a250, a251, a252, a253, a254, a255, a256, a257)
2.5.1 :005?>    puts 1
2.5.1 :006?>   end
 => :f
2.5.1 :001 > def f(a0 = 1, a1 = 1, a2 = 1, a3 = 1, a4 = 1, a5 = 1, a6 = 1, a7 = 1, a8 = 1, a9 = 1, a10 = 1, a11 = 1, a12 = 1, a13 = 1, a14 = 1, a15 = 1, a16 = 1, a17 = 1, a18 = 1, a19 = 1, a20 = 1, a21 = 1, a22 = 1, a23 = 1, a24 = 1, a25 = 1, a26 = 1, a27 = 1, a28 = 1, a29 = 1, a30 = 1, a31 = 1, a32 = 1, a33 = 1, a34 = 1, a35 = 1, a36 = 1, a37 = 1, a38 = 1, a39 = 1, a40 = 1, a41 = 1, a42 = 1, a43 = 1, a44 = 1, a45 = 1, a46 = 1, a47 = 1, a48 = 1, a49 = 1, a50 = 1, a51 = 1, a52 = 1, a53 = 1, a54 = 1, a55 = 1, a56 = 1, a57 = 1, a58 = 1, a59 = 1, a60 = 1, a61 = 1, a62 = 1, a63 = 1, a64 = 1, a65 = 1, a66 = 1, a67 = 1, a68 = 1, a69 = 1, a70 = 1, a71 = 1, a72 = 1, a73 = 1, a74 = 1, a75 = 1, a76 = 1, a77 = 1, a78 = 1, a79 = 1, a80 = 1, a81 = 1, a82 = 1, a83 = 1, a84 = 1, a85 = 1, a86 = 1, a87 = 1, a88 = 1, a89 = 1, a90 = 1, a91 = 1, a92 = 1, a93 = 1, a94 = 1, a95 = 1, a96 = 1, a97 = 1, a98 = 1, a99 = 1, a100 = 1, a101 = 1, a102 = 1, a103 = 1, a104 = 1, a105 = 1, a106 = 1, a107 = 1, a108 = 1, a109 = 1, a110 = 1, a111 = 1, a112 = 1, a113 = 1, a114 = 1, a115 = 1, a116 = 1, a117 = 1, a118 = 1, a119 = 1, a120 = 1, a121 = 1, a122 = 1, a123 = 1, a124 = 1, a125 = 1, a126 = 1, a127 = 1, a128 = 1, a129 = 1, a130 = 1, a131 = 1, a132 = 1, a133 = 1, a134 = 1, a135 = 1, a136 = 1, a137 = 1, a138 = 1, a139 = 1, a140 = 1, a141 = 1, a142 = 1, a143 = 1, a144 = 1, a145 = 1, a146 = 1, a147 = 1, a148 = 1, a149 = 1, a150 = 1, a151 = 1, a152 = 1, a153 = 1, a154 = 1, a155 = 1, a156 = 1, a157 = 1, a158 = 1, a159 = 1, a160 = 1, a161 = 1, a162 = 1, a163 = 1, a164 = 1, a165 = 1, a166 = 1, a167 = 1, a168 = 1, a169 = 1, a170 = 1, a171 = 1, a172 = 1, a173 = 1, a174 = 1, a175 = 1, a176 = 1, a177 = 1, a178 = 1, a179 = 1, a180 = 1, a181 = 1, a182 = 1, a183 = 1, a184 = 1, a185 = 1, a186 = 1, a187 = 1, a188 = 1, a189 = 1, a190 = 1, a191 = 1, a192 = 1, a193 = 1, a194 = 1, a195 = 1, a196 = 1, a197 = 1, a198 = 1, a199 = 1, a200 = 1, a201 = 1, a202 = 1, a203 = 1, a204 = 1, a205 = 1, a206 = 1, a207 = 1, a208 = 1, a209 = 1, a210 = 1, a211 = 1, a212 = 1, a213 = 1, a214 = 1, a215 = 1, a216 = 1, a217 = 1, a218 = 1, a219 = 1, a220 = 1, a221 = 1, a222 = 1, a223 = 1, a224 = 1, a225 = 1, a226 = 1, a227 = 1, a228 = 1, a229 = 1, a230 = 1, a231 = 1, a232 = 1, a233 = 1, a234 = 1, a235 = 1, a236 = 1, a237 = 1, a238 = 1, a239 = 1, a240 = 1, a241 = 1, a242 = 1, a243 = 1, a244 = 1, a245 = 1, a246 = 1, a247 = 1, a248 = 1, a249 = 1, a250 = 1, a251 = 1, a252 = 1, a253 = 1, a254 = 1, a255 = 1,  a256 = 1)
2.5.1 :002?>    puts 1
2.5.1 :003?>   end
 => :f 
2.5.1 :004 > f()
1
 => nil

Kotlin

定義はできているように見えます。しかし実行時にエラーが出ました。

>>> fun f(a0: Int, a1: Int, a2: Int, a3: Int, a4: Int, a5: Int, a6: Int, a7: Int, a8: Int, a9: Int, a10: Int, a11: Int, a12: Int, a13: Int, a14: Int, a15: Int, a16: Int, a17: Int, a18: Int, a19: Int, a20: Int, a21: Int, a22: Int, a23: Int, a24: Int, a25: Int, a26: Int, a27: Int, a28: Int, a29: Int, a30: Int, a31: Int, a32: Int, a33: Int, a34: Int, a35: Int, a36: Int, a37: Int, a38: Int, a39: Int, a40: Int, a41: Int, a42: Int, a43: Int, a44: Int, a45: Int, a46: Int, a47: Int, a48: Int, a49: Int, a50: Int, a51: Int, a52: Int, a53: Int, a54: Int, a55: Int, a56: Int, a57: Int, a58: Int, a59: Int, a60: Int, a61: Int, a62: Int, a63: Int, a64: Int, a65: Int, a66: Int, a67: Int, a68: Int, a69: Int, a70: Int, a71: Int, a72: Int, a73: Int, a74: Int, a75: Int, a76: Int, a77: Int, a78: Int, a79: Int, a80: Int, a81: Int, a82: Int, a83: Int, a84: Int, a85: Int, a86: Int, a87: Int, a88: Int, a89: Int, a90: Int, a91: Int, a92: Int, a93: Int, a94: Int, a95: Int, a96: Int, a97: Int, a98: Int, a99: Int, a100: Int, a101: Int, a102: Int, a103: Int, a104: Int, a105: Int, a106: Int, a107: Int, a108: Int, a109: Int, a110: Int, a111: Int, a112: Int, a113: Int, a114: Int, a115: Int, a116: Int, a117: Int, a118: Int, a119: Int, a120: Int, a121: Int, a122: Int, a123: Int, a124: Int, a125: Int, a126: Int, a127: Int, a128: Int, a129: Int, a130: Int, a131: Int, a132: Int, a133: Int, a134: Int, a135: Int, a136: Int, a137: Int, a138: Int, a139: Int, a140: Int, a141: Int, a142: Int, a143: Int, a144: Int, a145: Int, a146: Int, a147: Int, a148: Int, a149: Int, a150: Int, a151: Int, a152: Int, a153: Int, a154: Int, a155: Int, a156: Int, a157: Int, a158: Int, a159: Int, a160: Int, a161: Int, a162: Int, a163: Int, a164: Int, a165: Int, a166: Int, a167: Int, a168: Int, a169: Int, a170: Int, a171: Int, a172: Int, a173: Int, a174: Int, a175: Int, a176: Int, a177: Int, a178: Int, a179: Int, a180: Int, a181: Int, a182: Int, a183: Int, a184: Int, a185: Int, a186: Int, a187: Int, a188: Int, a189: Int, a190: Int, a191: Int, a192: Int, a193: Int, a194: Int, a195: Int, a196: Int, a197: Int, a198: Int, a199: Int, a200: Int, a201: Int, a202: Int, a203: Int, a204: Int, a205: Int, a206: Int, a207: Int, a208: Int, a209: Int, a210: Int, a211: Int, a212: Int, a213: Int, a214: Int, a215: Int, a216: Int, a217: Int, a218: Int, a219: Int, a220: Int, a221: Int, a222: Int, a223: Int, a224: Int, a225: Int, a226: Int, a227: Int, a228: Int, a229: Int, a230: Int, a231: Int, a232: Int, a233: Int, a234: Int, a235: Int, a236: Int, a237: Int, a238: Int, a239: Int, a240: Int, a241: Int, a242: Int, a243: Int, a244: Int, a245: Int, a246: Int, a247: Int, a248: Int, a249: Int, a250: Int, a251: Int, a252: Int, a253: Int, a254: Int, a255: Int, a256: Int, a257: Int) { println(1) }
>>> fun f(a0: Int = 1, a1: Int = 1, a2: Int = 1, a3: Int = 1, a4: Int = 1, a5: Int = 1, a6: Int = 1, a7: Int = 1, a8: Int = 1, a9: Int = 1, a10: Int = 1, a11: Int = 1, a12: Int = 1, a13: Int = 1, a14: Int = 1, a15: Int = 1, a16: Int = 1, a17: Int = 1, a18: Int = 1, a19: Int = 1, a20: Int = 1, a21: Int = 1, a22: Int = 1, a23: Int = 1, a24: Int = 1, a25: Int = 1, a26: Int = 1, a27: Int = 1, a28: Int = 1, a29: Int = 1, a30: Int = 1, a31: Int = 1, a32: Int = 1, a33: Int = 1, a34: Int = 1, a35: Int = 1, a36: Int = 1, a37: Int = 1, a38: Int = 1, a39: Int = 1, a40: Int = 1, a41: Int = 1, a42: Int = 1, a43: Int = 1, a44: Int = 1, a45: Int = 1, a46: Int = 1, a47: Int = 1, a48: Int = 1, a49: Int = 1, a50: Int = 1, a51: Int = 1, a52: Int = 1, a53: Int = 1, a54: Int = 1, a55: Int = 1, a56: Int = 1, a57: Int = 1, a58: Int = 1, a59: Int = 1, a60: Int = 1, a61: Int = 1, a62: Int = 1, a63: Int = 1, a64: Int = 1, a65: Int = 1, a66: Int = 1, a67: Int = 1, a68: Int = 1, a69: Int = 1, a70: Int = 1, a71: Int = 1, a72: Int = 1, a73: Int = 1, a74: Int = 1, a75: Int = 1, a76: Int = 1, a77: Int = 1, a78: Int = 1, a79: Int = 1, a80: Int = 1, a81: Int = 1, a82: Int = 1, a83: Int = 1, a84: Int = 1, a85: Int = 1, a86: Int = 1, a87: Int = 1, a88: Int = 1, a89: Int = 1, a90: Int = 1, a91: Int = 1, a92: Int = 1, a93: Int = 1, a94: Int = 1, a95: Int = 1, a96: Int = 1, a97: Int = 1, a98: Int = 1, a99: Int = 1, a100: Int = 1, a101: Int = 1, a102: Int = 1, a103: Int = 1, a104: Int = 1, a105: Int = 1, a106: Int = 1, a107: Int = 1, a108: Int = 1, a109: Int = 1, a110: Int = 1, a111: Int = 1, a112: Int = 1, a113: Int = 1, a114: Int = 1, a115: Int = 1, a116: Int = 1, a117: Int = 1, a118: Int = 1, a119: Int = 1, a120: Int = 1, a121: Int = 1, a122: Int = 1, a123: Int = 1, a124: Int = 1, a125: Int = 1, a126: Int = 1, a127: Int = 1, a128: Int = 1, a129: Int = 1, a130: Int = 1, a131: Int = 1, a132: Int = 1, a133: Int = 1, a134: Int = 1, a135: Int = 1, a136: Int = 1, a137: Int = 1, a138: Int = 1, a139: Int = 1, a140: Int = 1, a141: Int = 1, a142: Int = 1, a143: Int = 1, a144: Int = 1, a145: Int = 1, a146: Int = 1, a147: Int = 1, a148: Int = 1, a149: Int = 1, a150: Int = 1, a151: Int = 1, a152: Int = 1, a153: Int = 1, a154: Int = 1, a155: Int = 1, a156: Int = 1, a157: Int = 1, a158: Int = 1, a159: Int = 1, a160: Int = 1, a161: Int = 1, a162: Int = 1, a163: Int = 1, a164: Int = 1, a165: Int = 1, a166: Int = 1, a167: Int = 1, a168: Int = 1, a169: Int = 1, a170: Int = 1, a171: Int = 1, a172: Int = 1, a173: Int = 1, a174: Int = 1, a175: Int = 1, a176: Int = 1, a177: Int = 1, a178: Int = 1, a179: Int = 1, a180: Int = 1, a181: Int = 1, a182: Int = 1, a183: Int = 1, a184: Int = 1, a185: Int = 1, a186: Int = 1, a187: Int = 1, a188: Int = 1, a189: Int = 1, a190: Int = 1, a191: Int = 1, a192: Int = 1, a193: Int = 1, a194: Int = 1, a195: Int = 1, a196: Int = 1, a197: Int = 1, a198: Int = 1, a199: Int = 1, a200: Int = 1, a201: Int = 1, a202: Int = 1, a203: Int = 1, a204: Int = 1, a205: Int = 1, a206: Int = 1, a207: Int = 1, a208: Int = 1, a209: Int = 1, a210: Int = 1, a211: Int = 1, a212: Int = 1, a213: Int = 1, a214: Int = 1, a215: Int = 1, a216: Int = 1, a217: Int = 1, a218: Int = 1, a219: Int = 1, a220: Int = 1, a221: Int = 1, a222: Int = 1, a223: Int = 1, a224: Int = 1, a225: Int = 1, a226: Int = 1, a227: Int = 1, a228: Int = 1, a229: Int = 1, a230: Int = 1, a231: Int = 1, a232: Int = 1, a233: Int = 1, a234: Int = 1, a235: Int = 1, a236: Int = 1, a237: Int = 1, a238: Int = 1, a239: Int = 1, a240: Int = 1, a241: Int = 1, a242: Int = 1, a243: Int = 1, a244: Int = 1, a245: Int = 1, a246: Int = 1, a247: Int = 1, a248: Int = 1, a249: Int = 1, a250: Int = 1, a251: Int = 1, a252: Int = 1, a253: Int = 1, a254: Int = 1, a255: Int = 1) { println(1) }
>>> f()
java.lang.NullPointerException
        at Line_1.f$default(Line_1.kts:1)
>>> f(1)
java.lang.NullPointerException
        at Line_1.f$default(Line_1.kts:1)
>>> fun f(a0: Int = 1, a1: Int = 1, a2: Int = 1, a3: Int = 1, a4: Int = 1, a5: Int = 1, a6: Int = 1, a7: Int = 1, a8: Int = 1, a9: Int = 1, a10: Int = 1, a11: Int = 1, a12: Int = 1, a13: Int = 1, a14: Int = 1, a15: Int = 1, a16: Int = 1, a17: Int = 1, a18: Int = 1, a19: Int = 1, a20: Int = 1, a21: Int = 1, a22: Int = 1, a23: Int = 1, a24: Int = 1, a25: Int = 1, a26: Int = 1, a27: Int = 1, a28: Int = 1, a29: Int = 1, a30: Int = 1, a31: Int = 1, a32: Int = 1, a33: Int = 1, a34: Int = 1, a35: Int = 1, a36: Int = 1, a37: Int = 1, a38: Int = 1, a39: Int = 1, a40: Int = 1, a41: Int = 1, a42: Int = 1, a43: Int = 1, a44: Int = 1, a45: Int = 1, a46: Int = 1, a47: Int = 1, a48: Int = 1, a49: Int = 1, a50: Int = 1, a51: Int = 1, a52: Int = 1, a53: Int = 1, a54: Int = 1, a55: Int = 1, a56: Int = 1, a57: Int = 1, a58: Int = 1, a59: Int = 1, a60: Int = 1, a61: Int = 1, a62: Int = 1, a63: Int = 1, a64: Int = 1, a65: Int = 1, a66: Int = 1, a67: Int = 1, a68: Int = 1, a69: Int = 1, a70: Int = 1, a71: Int = 1, a72: Int = 1, a73: Int = 1, a74: Int = 1, a75: Int = 1, a76: Int = 1, a77: Int = 1, a78: Int = 1, a79: Int = 1, a80: Int = 1, a81: Int = 1, a82: Int = 1, a83: Int = 1, a84: Int = 1, a85: Int = 1, a86: Int = 1, a87: Int = 1, a88: Int = 1, a89: Int = 1, a90: Int = 1, a91: Int = 1, a92: Int = 1, a93: Int = 1, a94: Int = 1, a95: Int = 1, a96: Int = 1, a97: Int = 1, a98: Int = 1, a99: Int = 1, a100: Int = 1, a101: Int = 1, a102: Int = 1, a103: Int = 1, a104: Int = 1, a105: Int = 1, a106: Int = 1, a107: Int = 1, a108: Int = 1, a109: Int = 1, a110: Int = 1, a111: Int = 1, a112: Int = 1, a113: Int = 1, a114: Int = 1, a115: Int = 1, a116: Int = 1, a117: Int = 1, a118: Int = 1, a119: Int = 1, a120: Int = 1, a121: Int = 1, a122: Int = 1, a123: Int = 1, a124: Int = 1, a125: Int = 1, a126: Int = 1, a127: Int = 1, a128: Int = 1, a129: Int = 1, a130: Int = 1, a131: Int = 1, a132: Int = 1, a133: Int = 1, a134: Int = 1, a135: Int = 1, a136: Int = 1, a137: Int = 1, a138: Int = 1, a139: Int = 1, a140: Int = 1, a141: Int = 1, a142: Int = 1, a143: Int = 1, a144: Int = 1, a145: Int = 1, a146: Int = 1, a147: Int = 1, a148: Int = 1, a149: Int = 1, a150: Int = 1, a151: Int = 1, a152: Int = 1, a153: Int = 1, a154: Int = 1, a155: Int = 1, a156: Int = 1, a157: Int = 1, a158: Int = 1, a159: Int = 1, a160: Int = 1, a161: Int = 1, a162: Int = 1, a163: Int = 1, a164: Int = 1, a165: Int = 1, a166: Int = 1, a167: Int = 1, a168: Int = 1, a169: Int = 1, a170: Int = 1, a171: Int = 1, a172: Int = 1, a173: Int = 1, a174: Int = 1, a175: Int = 1, a176: Int = 1, a177: Int = 1, a178: Int = 1, a179: Int = 1, a180: Int = 1, a181: Int = 1, a182: Int = 1, a183: Int = 1, a184: Int = 1, a185: Int = 1, a186: Int = 1, a187: Int = 1, a188: Int = 1, a189: Int = 1, a190: Int = 1, a191: Int = 1, a192: Int = 1, a193: Int = 1, a194: Int = 1, a195: Int = 1, a196: Int = 1, a197: Int = 1, a198: Int = 1, a199: Int = 1, a200: Int = 1, a201: Int = 1, a202: Int = 1, a203: Int = 1, a204: Int = 1, a205: Int = 1, a206: Int = 1, a207: Int = 1, a208: Int = 1, a209: Int = 1, a210: Int = 1, a211: Int = 1, a212: Int = 1, a213: Int = 1, a214: Int = 1, a215: Int = 1, a216: Int = 1, a217: Int = 1, a218: Int = 1, a219: Int = 1, a220: Int = 1, a221: Int = 1, a222: Int = 1, a223: Int = 1, a224: Int = 1, a225: Int = 1, a226: Int = 1, a227: Int = 1, a228: Int = 1, a229: Int = 1, a230: Int = 1, a231: Int = 1, a232: Int = 1, a233: Int = 1, a234: Int = 1, a235: Int = 1, a236: Int = 1, a237: Int = 1, a238: Int = 1, a239: Int = 1, a240: Int = 1, a241: Int = 1, a242: Int = 1, a243: Int = 1, a244: Int = 1, a245: Int = 1, a246: Int = 1, a247: Int = 1, a248: Int = 1, a249: Int = 1,  a250: Int = 1,  a251: Int = 1,  a252: Int = 1,  a253: Int = 1,  a254: Int = 1) { println(1) }
>>> f()
1
>>>

Java

256個以上のパラメータがあると、定義することもできません。

jshell> void f(int a0, int a1, int a2, int a3, int a4, int a5, int a6, int a7, int a8, int a9, int a10, int a11, int a12, int a13, int a14, int a15, int a16, int a17, int a18, int a19, int a20, int a21, int a22, int a23, int a24, int a25, int a26, int a27, int a28, int a29, int a30, int a31, int a32, int a33, int a34, int a35, int a36, int a37, int a38, int a39, int a40, int a41, int a42, int a43, int a44, int a45, int a46, int a47, int a48, int a49, int a50, int a51, int a52, int a53, int a54, int a55, int a56, int a57, int a58, int a59, int a60, int a61, int a62, int a63, int a64, int a65, int a66, int a67, int a68, int a69, int a70, int a71, int a72, int a73, int a74, int a75, int a76, int a77, int a78, int a79, int a80, int a81, int a82, int a83, int a84, int a85, int a86, int a87, int a88, int a89, int a90, int a91, int a92, int a93, int a94, int a95, int a96, int a97, int a98, int a99, int a100, int a101, int a102, int a103, int a104, int a105, int a106, int a107, int a108, int a109, int a110, int a111, int a112, int a113, int a114, int a115, int a116, int a117, int a118, int a119, int a120, int a121, int a122, int a123, int a124, int a125, int a126, int a127, int a128, int a129, int a130, int a131, int a132, int a133, int a134, int a135, int a136, int a137, int a138, int a139, int a140, int a141, int a142, int a143, int a144, int a145, int a146, int a147, int a148, int a149, int a150, int a151, int a152, int a153, int a154, int a155, int a156, int a157, int a158, int a159, int a160, int a161, int a162, int a163, int a164, int a165, int a166, int a167, int a168, int a169, int a170, int a171, int a172, int a173, int a174, int a175, int a176, int a177, int a178, int a179, int a180, int a181, int a182, int a183, int a184, int a185, int a186, int a187, int a188, int a189, int a190, int a191, int a192, int a193, int a194, int a195, int a196, int a197, int a198, int a199, int a200, int a201, int a202, int a203, int a204, int a205, int a206, int a207, int a208, int a209, int a210, int a211, int a212, int a213, int a214, int a215, int a216, int a217, int a218, int a219, int a220, int a221, int a222, int a223, int a224, int a225, int a226, int a227, int a228, int a229, int a230, int a231, int a232, int a233, int a234, int a235, int a236, int a237, int a238, int a239, int a240, int a241, int a242, int a243, int a244, int a245, int a246, int a247, int a248, int a249, int a250, int a251, int a252, int a253, int a254,  int a255) { System.out.println(1); }
|  Error:
|  too many parameters
|  void f(int a0, int a1, int a2, int a3, int a4, int a5, int a6, int a7, int a8, int a9, int a10, int a11, int a12, int a13, int a14, int a15, int a16, int a17, int a18, int a19, int a20, int a21, int a22, int a23, int a24, int a25, int a26, int a27, int a28, int a29, int a30, int a31, int a32, int a33, int a34, int a35, int a36, int a37, int a38, int a39, int a40, int a41, int a42, int a43, int a44, int a45, int a46, int a47, int a48, int a49, int a50, int a51, int a52, int a53, int a54, int a55, int a56, int a57, int a58, int a59, int a60, int a61, int a62, int a63, int a64, int a65, int a66, int a67, int a68, int a69, int a70, int a71, int a72, int a73, int a74, int a75, int a76, int a77, int a78, int a79, int a80, int a81, int a82, int a83, int a84, int a85, int a86, int a87, int a88, int a89, int a90, int a91, int a92, int a93, int a94, int a95, int a96, int a97, int a98, int a99, int a100, int a101, int a102, int a103, int a104, int a105, int a106, int a107, int a108, int a109, int a110, int a111, int a112, int a113, int a114, int a115, int a116, int a117, int a118, int a119, int a120, int a121, int a122, int a123, int a124, int a125, int a126, int a127, int a128, int a129, int a130, int a131, int a132, int a133, int a134, int a135, int a136, int a137, int a138, int a139, int a140, int a141, int a142, int a143, int a144, int a145, int a146, int a147, int a148, int a149, int a150, int a151, int a152, int a153, int a154, int a155, int a156, int a157, int a158, int a159, int a160, int a161, int a162, int a163, int a164, int a165, int a166, int a167, int a168, int a169, int a170, int a171, int a172, int a173, int a174, int a175, int a176, int a177, int a178, int a179, int a180, int a181, int a182, int a183, int a184, int a185, int a186, int a187, int a188, int a189, int a190, int a191, int a192, int a193, int a194, int a195, int a196, int a197, int a198, int a199, int a200, int a201, int a202, int a203, int a204, int a205, int a206, int a207, int a208, int a209, int a210, int a211, int a212, int a213, int a214, int a215, int a216, int a217, int a218, int a219, int a220, int a221, int a222, int a223, int a224, int a225, int a226, int a227, int a228, int a229, int a230, int a231, int a232, int a233, int a234, int a235, int a236, int a237, int a238, int a239, int a240, int a241, int a242, int a243, int a244, int a245, int a246, int a247, int a248, int a249, int a250, int a251, int a252, int a253, int a254,  int a255) { System.out.println(1); }
|  ^----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------^
|  modified method f(int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int), however, it cannot be referenced until this error is corrected: 
|      too many parameters
|      void f(int a0, int a1, int a2, int a3, int a4, int a5, int a6, int a7, int a8, int a9, int a10, int a11, int a12, int a13, int a14, int a15, int a16, int a17, int a18, int a19, int a20, int a21, int a22, int a23, int a24, int a25, int a26, int a27, int a28, int a29, int a30, int a31, int a32, int a33, int a34, int a35, int a36, int a37, int a38, int a39, int a40, int a41, int a42, int a43, int a44, int a45, int a46, int a47, int a48, int a49, int a50, int a51, int a52, int a53, int a54, int a55, int a56, int a57, int a58, int a59, int a60, int a61, int a62, int a63, int a64, int a65, int a66, int a67, int a68, int a69, int a70, int a71, int a72, int a73, int a74, int a75, int a76, int a77, int a78, int a79, int a80, int a81, int a82, int a83, int a84, int a85, int a86, int a87, int a88, int a89, int a90, int a91, int a92, int a93, int a94, int a95, int a96, int a97, int a98, int a99, int a100, int a101, int a102, int a103, int a104, int a105, int a106, int a107, int a108, int a109, int a110, int a111, int a112, int a113, int a114, int a115, int a116, int a117, int a118, int a119, int a120, int a121, int a122, int a123, int a124, int a125, int a126, int a127, int a128, int a129, int a130, int a131, int a132, int a133, int a134, int a135, int a136, int a137, int a138, int a139, int a140, int a141, int a142, int a143, int a144, int a145, int a146, int a147, int a148, int a149, int a150, int a151, int a152, int a153, int a154, int a155, int a156, int a157, int a158, int a159, int a160, int a161, int a162, int a163, int a164, int a165, int a166, int a167, int a168, int a169, int a170, int a171, int a172, int a173, int a174, int a175, int a176, int a177, int a178, int a179, int a180, int a181, int a182, int a183, int a184, int a185, int a186, int a187, int a188, int a189, int a190, int a191, int a192, int a193, int a194, int a195, int a196, int a197, int a198, int a199, int a200, int a201, int a202, int a203, int a204, int a205, int a206, int a207, int a208, int a209, int a210, int a211, int a212, int a213, int a214, int a215, int a216, int a217, int a218, int a219, int a220, int a221, int a222, int a223, int a224, int a225, int a226, int a227, int a228, int a229, int a230, int a231, int a232, int a233, int a234, int a235, int a236, int a237, int a238, int a239, int a240, int a241, int a242, int a243, int a244, int a245, int a246, int a247, int a248, int a249, int a250, int a251, int a252, int a253, int a254,  int a255) { System.out.println(1); }
|      ^----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------^

jshell> void f(int a0, int a1, int a2, int a3, int a4, int a5, int a6, int a7, int a8, int a9, int a10, int a11, int a12, int a13, int a14, int a15, int a16, int a17, int a18, int a19, int a20, int a21, int a22, int a23, int a24, int a25, int a26, int a27, int a28, int a29, int a30, int a31, int a32, int a33, int a34, int a35, int a36, int a37, int a38, int a39, int a40, int a41, int a42, int a43, int a44, int a45, int a46, int a47, int a48, int a49, int a50, int a51, int a52, int a53, int a54, int a55, int a56, int a57, int a58, int a59, int a60, int a61, int a62, int a63, int a64, int a65, int a66, int a67, int a68, int a69, int a70, int a71, int a72, int a73, int a74, int a75, int a76, int a77, int a78, int a79, int a80, int a81, int a82, int a83, int a84, int a85, int a86, int a87, int a88, int a89, int a90, int a91, int a92, int a93, int a94, int a95, int a96, int a97, int a98, int a99, int a100, int a101, int a102, int a103, int a104, int a105, int a106, int a107, int a108, int a109, int a110, int a111, int a112, int a113, int a114, int a115, int a116, int a117, int a118, int a119, int a120, int a121, int a122, int a123, int a124, int a125, int a126, int a127, int a128, int a129, int a130, int a131, int a132, int a133, int a134, int a135, int a136, int a137, int a138, int a139, int a140, int a141, int a142, int a143, int a144, int a145, int a146, int a147, int a148, int a149, int a150, int a151, int a152, int a153, int a154, int a155, int a156, int a157, int a158, int a159, int a160, int a161, int a162, int a163, int a164, int a165, int a166, int a167, int a168, int a169, int a170, int a171, int a172, int a173, int a174, int a175, int a176, int a177, int a178, int a179, int a180, int a181, int a182, int a183, int a184, int a185, int a186, int a187, int a188, int a189, int a190, int a191, int a192, int a193, int a194, int a195, int a196, int a197, int a198, int a199, int a200, int a201, int a202, int a203, int a204, int a205, int a206, int a207, int a208, int a209, int a210, int a211, int a212, int a213, int a214, int a215, int a216, int a217, int a218, int a219, int a220, int a221, int a222, int a223, int a224, int a225, int a226, int a227, int a228, int a229, int a230, int a231, int a232, int a233, int a234, int a235, int a236, int a237, int a238, int a239, int a240, int a241, int a242, int a243, int a244, int a245, int a246, int a247, int a248, int a249, int a250, int a251, int a252, int a253,  int a254) { System.out.println(1); }
|  created method f(int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int)

jshell> f(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  1);
1

jshell>

JavaScript

パラメータが256個以上でも関数定義できます・

function f(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, a31, a32, a33, a34, a35, a36, a37, a38, a39, a40, a41, a42, a43, a44, a45, a46, a47, a48, a49, a50, a51, a52, a53, a54, a55, a56, a57, a58, a59, a60, a61, a62, a63, a64, a65, a66, a67, a68, a69, a70, a71, a72, a73, a74, a75, a76, a77, a78, a79, a80, a81, a82, a83, a84, a85, a86, a87, a88, a89, a90, a91, a92, a93, a94, a95, a96, a97, a98, a99, a100, a101, a102, a103, a104, a105, a106, a107, a108, a109, a110, a111, a112, a113, a114, a115, a116, a117, a118, a119, a120, a121, a122, a123, a124, a125, a126, a127, a128, a129, a130, a131, a132, a133, a134, a135, a136, a137, a138, a139, a140, a141, a142, a143, a144, a145, a146, a147, a148, a149, a150, a151, a152, a153, a154, a155, a156, a157, a158, a159, a160, a161, a162, a163, a164, a165, a166, a167, a168, a169, a170, a171, a172, a173, a174, a175, a176, a177, a178, a179, a180, a181, a182, a183, a184, a185, a186, a187, a188, a189, a190, a191, a192, a193, a194, a195, a196, a197, a198, a199, a200, a201, a202, a203, a204, a205, a206, a207, a208, a209, a210, a211, a212, a213, a214, a215, a216, a217, a218, a219, a220, a221, a222, a223, a224, a225, a226, a227, a228, a229, a230, a231, a232, a233, a234, a235, a236, a237, a238, a239, a240, a241, a242, a243, a244, a245, a246, a247, a248, a249, a250, a251, a252, a253, a254, a255) { console.log(1); }
f(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1);
1

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投稿日：2019-02-11T12:24:48+09:00

KotlinとThymeleafでハマったこと

背景

前回書いた記事でThymeleafを使った簡単なアプリケーションを実装した

その際にisNewというbooleanの変数をDTOに定義して、Thymeleafからアクセスしようとしたが、なぜか取得できなかった

ソース

ソースは以下の感じ

isNewというフラグで画像の表示をするか判定してるだけ
top.html
<div style="float: left; margin: 5px" th:each="image, index:${imageResources}">
　　　　
　　　　　　　　<img th:src="@{img/new.png}" style="width:30px; height:30px">
　　　　
下がtop画面に表示させるためのレスポンスクラス
LgtmTopResponse.kt
class LgtmTopResponse {
 var imageUrl = String()
 var imageName = String()
 var imageLgtmUrl = String()
 var updateDatetime = Date()
 var isNew = false

 fun buildWithEntity(lgtmEntity: LgtmEntity,baseDate :Date) : LgtmTopResponse{
 return LgtmTopResponse().apply {
 imageUrl = lgtmEntity.imageUrl
 imageName = lgtmEntity.imageName
 imageLgtmUrl = lgtmEntity.imageLgtmUrl
 updateDatetime = lgtmEntity.updateDatetime
 isNew = lgtmEntity.updateDatetime.after(baseDate)
 }
 }
}
このまま実行すると怒られた

原因と対策

原因としては、kotlinでisNewというプロパティがコンパイルを実行すると、newという変数名に変換されてしまうっぽい

なので、Thymeleafからはisを外したプロパティ名でアクセスすれば動く

もしくはメソッドアクセスみたいな感じで、isNew()でも動くっぽい

どっちで書くのが良いのかはまだわかってないです

ソースを修正
top.html

　　　　<img th:src="@{img/new.png}" style="width:30px; height:30px">

または、こっち
top.html

　　　　<img th:src="@{img/new.png}" style="width:30px; height:30px">

まとめ

Javaでつくったアプリケーションのサーバー側をKotlinに書き換える際に、フロントを全くいじらなくて良いという訳ではなさそう

is〇〇って名前はちょいちょい使うので、これはちょっとイケてないなーと思った

とはいえ、Kotlinはやっぱり楽しい

参考リンク

Thymeleaf で isXxx プロパティを参照するとエラーになる

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投稿日：2019-02-11T10:44:35+09:00

Java開発者に送るKotlinのスコープ関数

スコープ関数とは

Kotlinの標準ライブラリに定義されているジェネリック関数。
ジェネリック関数なので、どんな型にも適用できる関数です。
スコープ関数を使うことで、よりKotlinらしいコードが書けます。

letとrun

Streamのmap関数のようなイメージです。
val str: String = "5963"

// 変数strをIntに変換する
// letを使った場合
val i: Int = str.let { it.toInt() }

// 変数strをIntに変換する
// runを使った場合
val i2: Int = str.run { this.toInt() }
letに続くラムダ式は引数が1つです。この引数はstrへの参照です。
runに続くラムダ式は引数がありません。代わりに、このラムダ式内のthis参照はstrです。
ラムダ式の結果がlet、runの戻り値となります。

また、今回の例の変数strのような、関数の呼び出されるオブジェクトをレイシーバーオブジェクトといいます。

使いどころ
fun getName(): String? = ""
fun makeGreeting(name: String) = "Hello, $name"

fun greet(): String? {
    val name = getName()
    if (name == null) {
        return null
    }

    return makeGreeting(name)
}
greet()関数では
getName()の結果を、makeGreeting()関数に渡し、
その結果がgreet()関数の戻り値となります。

ただし、getName()の戻り値はnull許容型なので、一度nullチェックが必要です。
これを、letを使って書き換えてみます。
fun greet(): String? {
    return getName()?.let { makeGreeting(it) }
}
getName()の結果を安全呼び出しを使い、letを呼び出します。
こうすると、かなりスッキリ書けます。
安全呼び出しや、安全キャストの結果を関数の引数に渡す場合に便利です。
(もちろん、それ以外の場合にもよく使われます。)

applyとalso

letとrunに似ていますが、戻り値は常にレシーバーオブジェクトです。
val str: String = "5963"

// 変数strを標準出力
// alsoを使った場合
val str2: String = str.also { print(it) }

// 変数strを標準出力
// applyを使った場合
val str3: String = str.apply { print(this) }
使いどころ
class Person {
    var firstName: String? = null
    var middleName: String? = null
    var lastName: String? = null
}

fun registerNewPerson() : Person {
    val person = Person()
    person.firstName = "久美子"
    person.middleName = "スーザン"
    person.lastName = "山本"
    return person
}
registerNewPerson関数では、Personのインスタンスを新たに作って返します。
Personを初期化するだけですが、一旦変数に置かなければなりません。

alsoを使ってみましょう。
fun registerNewPerson() : Person {
    return Person().also {
        it.firstName = "久美子"
        it.middleName = "スーザン"
        it.lastName = "山本"
    }
}
Personの一時変数を作らずに実装できます。
Builderパターンでは無いオブジェクトを扱う場合などに、
そのオブジェクトの初期化処理がスコープ関数の中にまとまるので、可読性向上につながります。

with

withはちょっと変わりダネです。
レシーバーオブジェクトを引数で渡すrun っといったところです。
val str = "5963"
val i: Int = with(str) { this.toInt() }
使いどころ
class Greeter {
    fun greet(): String = "Hello, world"
}

fun greet(greeter: Greeter) = with(greeter) { 
    greet()
}
withを使って単一式関数にします。
this参照が変わり違った文脈で記述できるようになります。

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投稿日：2019-02-11T10:43:54+09:00

Java開発者に送るKotlinとの相互運用Tips

KotlinコードをJavaから呼び出すとき

デフォルト引数

Kotlinのデフォルト引数付き関数をJavaから扱いたい場合、全ての引数を指定しなければなりません。
ですが、関数に@JvmOverloadアノテーションを付加すると自動的にオーバーロードメソッドが生成されます。
// Kotlin
class OverloadSample {
    @JvmOverloads // アノテーションをつけると、Javaから呼び出し可能なオーバーロードメソッドが生成される
    fun test(arg1: Boolean = true, arg2: Int = 1, arg3: String = "true") : Boolean {
        return arg1 && arg2 == 1 && arg3 == "true"
    }
}
Javaからの呼び出しコードを実装してみます。
// Java
OverloadSample os = new OverloadSample();
os.test(true, 1, "true");
os.test(true, 1);
os.test(true);
トップレベル関数、プロパティ

クラスに属さないトップレベルのKotlin関数をJavaから呼び出す方法です。
Kotlinのトップレベル関数は
ソースファイル名+Ktという名前のクラスが生成され、
そのクラスのstatic関数へコンパイルされます。
// Utility.kt
fun doSomething() {
    // Do something
}
// Java
UtilityKt.doSomething();
上記のソースファイル名+Ktというクラス名を変更したい場合は@JvmNameアノテーションを使います。このアノテーションはパッケージに記述しまし。
// Utility.kt
@file: JvmName("Util")
package com.sample

fun doSomething() {
    // Do something
}
// Java
Util.doSomething();
拡張関数

拡張関数はトップレベル関数と同じく、ソースファイル名+Ktという名前のクラスのstatic関数としてコンパイルされます。Javaから呼び出す場合は、thisとなるオブジェクトが第一引数となります。
// StringUtility.kt
fun String.join(otherString: String) : String {
    return this + otherString
}
// Java
StringUtilityKt.join("Hello, ", "World!");
objectクラス

objectクラスをJavaからみると、INSTANCEというstaticフィールドを持ったクラスとなります。objectクラスのプロパティか関数にアクセスするには、このINSTANCEを経由します。
// Kotlin
object LogUtil {
    fun debug(log: String) {
        //
    }
}
// Java
LogUtil.INSTANCE.debug("completed!");
JavaコードをKotlinから呼び出すとき

プラットフォーム型

Java関数の戻り値をKotlinコードで受ける場合など、
その戻り値がnull許容型か否かは@NonNullと@Nullableの
アノテーションで判断されます。
// Java
public class Sample {

    @NonNull
    String getString1() {
        return //
    }

    @Nullable
    String getString2() {
        return //
    }
}
Kotlinで呼び出すと以下のようになります。
// Kotlin
val sample = Sample()
val str1 = sample.string1 // 非null許容型
val str2 = sample.string2 // null許容型
ただし、@NonNullや@Nullableのアノテーションは
コンパイル時に強制力を持つものではないので注意が必要です。

では、アノテーションをつけない場合は...
// Java
public class Sample {
    // アノテーション無し
    String getString3() {
        return  //
    }
}
Kotlinから呼び出してみます。
// Kotlin
val sample = Sample()
val str3 = sample.string3 // String!
String!という型になります。
この!のついた型をプラットフォーム型といいます。

null許容型でも非null許容型でも扱える、どっちも型です。
Nullであるか否かを開発者に委ねる考え方です。
// Kotlin
val sample = Sample()
val str = sample.string3
val length = str.length // 非null許容型として扱う
val char = str?.get(0) // null許容型として扱う
static関数、staticフィールド

何らかの理由でstatic関数やフィールドが必要な状況があり得ます。
例えば...

Kotlinでstaticっぽく使えるcompanion object。
ここでアノテーションを使うと、Javaのstaticとしてコンパイルされます。
// Kotlin
class Sample {
    companion object {

        @JvmField // staticフィールドへのコンパイルを指定するアノテーション
        var TAG: String = "Sample"

        @JvmStatic // static関数へのコンパイルを指定するアノテーション
        fun tag(): String {
            return "Sample"
        }
    }
}
// Java
String tag = Sample.TAG;
tag = Sample.tag();
SAM変換

特定の条件下において、
Javaのインターフェースを実装したクラスをラムダ式で作ることができます。
val executor: ThreadPoolExecutor

// executeメソッドの引数にはRunnableを実装したオブジェクトを渡す
executor.execute(object: Runnable{
    override fun run() {
        //
    }
})

// SAM変換により、ラムダ式で表現可能！
executor.execute { 
    //
}
KotlinでSAM変換が有効となる条件は以下です。

Javaで宣言されたインターフェースであること

抽象メソッドが1つだけのインターフェースであること

Kotlinには適切な関数型が存在するのでKotlinで宣言したインターフェースではSAM変換は有効になりません

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投稿日：2019-02-11T07:15:08+09:00

kotlinでAndroid端末内の画像を含むフォルダを検知する

画像系のアプリを作ってる時に端末内の画像を含むフォルダを表示させたかったので作成

ストレージの許可

端末の設定からアプリのストレージ設定を弄らないと内部ストレージにアクセスできない？らしい
詳しくはhttps://direct.fujixerox.co.jp/ap1/sc/beat/ja/support/020211.html

内部ストレージのパスを渡す

内部ストレージのパスをImgFileconクラスのimgfileserchに渡す

MainActivity.kt

package com.example.myapplication

import android.os.Bundle
import android.support.design.widget.BottomNavigationView
import android.support.v7.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import java.io.File
import com.example.myapplication.R.attr.content
import android.content.Context
import android.os.Environment

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        /*内部ストレージのパス取得*/
        val path = Environment.getExternalStorageDirectory().getPath()
        val dir  = File(path)

      /*内部ストレージのパスを渡す*/
      val imgserch=ImgFilecon()
      imgserch.imgfileserch(dir.toString())
    }
}

画像を含むフォルダを探す

渡されたパス内のディレクトを再帰的に探索してファイルを探す。見つけたファイルが画像の拡張子(.jpgなど)を持っていたらそのファイルのあるディレクトリのパスを出力
余計な画像が出てきてしまうためAndroidフォルダはリジェクト

ImgFilecon.kt

package com.example.myapplication

import android.os.Parcel
import android.os.Parcelable
import java.io.File

class ImgFilecon() {
   /*画像の含まれるディレクトリを再帰的に探すメソッド*/
    tailrec fun imgfileserch(passname: String): Unit {

       var flag = false
       val dir = File(passname)

       if (dir.listFiles() != null) {
           /*渡されたパスを探査*/
           loop@ for (i in dir.listFiles()) {

            /*ファイルの時の処理*/
            if (i.isFile()) {
              val ext = Extension()
               /*画像ファイル判定*/
               if (!flag) {
                 when (ext.extensionsplit(i.toString(), ".")) {
                   "jpeg", "JPEG", "jpg", "JPG", "png", "PNG", "gif", "GIF" -> {
                           println("画像の含まれるディレクトリのパス" + dir)
                           flag = true
                           }
                           else -> {}
                       }
                   }
               }

             /*ディレクトリの時の処理*/
             else if (i.isDirectory) {
                   val extdir = Extension()
                   /*Androidディレクトリは余計な画像が含まれるので表示しない*/
                   when (extdir.extensionsplit(i.toString(), "0/")) {
                       "/Android" -> {
                           continue@loop
                       }
                       else -> {
                      /*再帰*/
                        imgfileserch(i.toString())
                       }
                   }
               }

           }
       } else println("null")
   }
}

画像ファイルを判断するために拡張子切り出し

パスと区切り文字を渡すと区切り文字より下の文字列を返すメソッド。今回はファイルパスと区切り文字"."を渡して拡張子を取得した。

Extension.kt

package com.example.myapplication

import android.os.Parcel
import android.os.Parcelable

class Extension {

    /*区切り文字で分割するメソッド*/
     fun extensionsplit(filename: String, splitps: String): String {

        /*splitpsで指定した文字のindex*/
         val point = filename.lastIndexOf(splitps)

         if (point != -1) {
             /*pointより下の部分を切り出す*/
             /* 例 xxxx.jpg→jpg*/
             return filename.substring(startIndex = point + 1)
         }
         else return null.toString()
     }
}

デモ

こんな感じで端末内の画像を含むフォルダ一覧がAndroidStudioのRunに表示される

参考

ストレージへのアクセス許可:https://direct.fujixerox.co.jp/ap1/sc/beat/ja/support/020211.html

終わりに

Github：https://github.com/tf0101/MyApplication4

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20190211のKotlinに関する記事は6件です。

Kotlinのforループで独自クラスをイテレートする方法

概要

rangeTo と ClosedRange

実装例

ソースコード

各言語で定義できる関数のパラメータの最大個数

Python

PHP

Ruby

Kotlin

Java

JavaScript

KotlinとThymeleafでハマったこと

背景

ソース

このまま実行すると怒られた

原因と対策

ソースを修正

まとめ

参考リンク

Java開発者に送るKotlinのスコープ関数

スコープ関数とは

letとrun

applyとalso

with

Java開発者に送るKotlinとの相互運用Tips

KotlinコードをJavaから呼び出すとき

デフォルト引数

トップレベル関数、プロパティ

拡張関数

objectクラス

JavaコードをKotlinから呼び出すとき

プラットフォーム型

static関数、staticフィールド

SAM変換