JEP 455: Primitive Types in Patterns, instanceof, and switch (Preview)

JJUG ナイトセミナー 2024年9月

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1. JEP 455： Primitive Types in Patterns, instanceof, and switch (Preview) 2024/09/12 JJUGナイトセミナー
2. Θͨ͠ • Α͜ͳ☕
   !JIDPNFHB
   • ʰ͍ͪ͹Μ΍͍͞͠(JU(JU)VCͷڭՊॻʱ
   • ΞϝϦΧ͔Βؼࠃ͠೥ʂ
   • ࢲ΋΂ΖΜ΂ΖΜʹͳΔͷ͕޷͖
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   ʢ++6(װࣄͷօ͞Μ͢Έ·ͤΜʣ 2
3. ࠓ೔ͷςʔϚ͸
   ύλʔϯϚον🤝 3 コードを書くときの 機能を改善する取り組み Project Amberの⼀部
4. ࢹ֮తʹίʔυͷมԽΛݟͯ
   ڵຯΛ͍͖͍࣋ͬͯͨͩͨʂ 4
5. ίϯύΠϥͷ͓ؾ࣋ͪͱ͔͸
   આ໌Ͱ͖ͳ͍ͷͰ
   ѱ͔͠Βͣʜ 5
6. ύλʔϯϚονͱ͸
   Ұൠ࿦ • ෼͔Γ΍͘͢ݴ͏ͱ৚݅൑ఆͷͻͱͭ
   • ஋Λύλʔϯͱর߹͠ɺҰக Ϛον ͢Δ͔֬ೝ͢Δ
   • Ұக͔ͨ͠Ͳ͏͔Ͱ৚݅෼ذ͕Ͱ͖Δ͚ͩͰͳ͘ɺɹɹɹɹɹ ஋Λ෼ղͯ͠࢖͏͜ͱ͕Ͱ͖Δ 6
7. ύλʔϯϚονͱ͸
   Ұൠ࿦ “Ն” “य़” “Ն” “ळ” “ౙ” 7
8. ύλʔϯϚονͱ͸
   Ұൠ࿦ 🌻
   
   🌹
   
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   🌷 🌸
   
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   🌸 🌷
   
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   ❓ ❓ 💐
   
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   💐
   
   💐 8
9. ύλʔϯϚονͱ͸
   Ұൠ࿦ʣ 🌻
   
   🌹
   
   🌸
   
   🌷 🌻
   
   🌹
   
   ❓
   
   🌷 B
   ʹ
   🌹 র߹ ෼ղ C
   ʹ
   🌸 9
10. γϯϓϧͳྫ String season = "Ն"; String result = switch (season) { ɹɹcase "य़" -> "Spring"; ɹɹcase "Ն" -> "Summer"; ɹɹcase "ळ" -> "Fall"; ɹɹcase "ౙ" -> "Winter"; ɹɹdefault -> "something wrong"; } 10 定数パターン というやつ
11. ·ͣ͸
    ύλʔϯϚονΛ
    ͔ͭ΋͏ 11
12. ࢖͏ྫͷ঺հʢৄࡉ͸ޙ΄Ͳʣ 12 sealed interface UserAction permits Click, Drag, Scroll {} record Click(int x, int y) implements UserAction {} record Drag(int startX, int startY, int endX, int endY) implements UserAction {} record Scroll(int amount) implements UserAction {}
13. JOTUBODFPG
    ͰύλʔϯϚον 13 if (action instanceof Click) { Click click = (Click) action; System.out.println("Clicked " + click.getX() + ", " + click.getY()); } if (action instanceof Click click) { System.out.println("Clicked " + click.getX() + ", " + click.getY()); } キャスト不要で 簡潔かつ安全
14. TXJUDI
    ͰύλʔϯϚον 14 if (action instanceof Click) { Click c = (Click) action; result = "Clicked " + c.getX() + ", " + c.getY(); } else if (action instanceof Drag) { Drag d = (Drag) action; result = "Dragged " + d.startX() + " to " + d.endX(); } else if (action instanceof Scroll) { Scroll s = (Scroll) action; result = "Scrolled " + s.getAmount(); } else { result = "Unknown action"; }
15. TXJUDI
    ͰύλʔϯϚον 15 String result = switch (action) { case Click c -> "Clicked " + c.x() + ", " + c.y(); case Drag d -> "Dragged " + d.startX() + " to " + d.endX(); case Scroll s -> "Scrolled " + s.amount(); }; オブジェクト型で パターンマッチ、 かなり簡潔！ 判定と使⽤を 分けずに書ける タイプパターン というやつ パターン変数 スコープはマッチしたケースの中のみ
16. TXJUDI
    ͰύλʔϯϚον 16 String result = switch (action) { case Click c -> "Clicked " + c.x() + ", " + c.y(); case Drag d -> "Dragged " + d.startX() + " to " + d.endX(); case Scroll s -> "Scrolled " + s.amount(); }; String result = switch (action) { case Click(int x, int y) -> "Clicked " + x + ", " + y; case Drag(int startX, int startY, int endX, int endY) -> "Dragged " + startX + " to " + endX; case Scroll(int amount) -> "Scrolled " + amount; }; Recordを使って 構造を活⽤ 値の分解も可能
17. 3FDPSEɺγʔϧ 17 sealed interface UserAction permits Click, Drag, Scroll {} record Click(int x, int y) implements UserAction {} record Drag(int startX, int startY, int endX, int endY) implements UserAction {} record Scroll(int amount) implements UserAction {} Recordでクラス定義の ボイラープレートを減らせる (getter, equals, hashCode, toString) パターンの網羅性を担保、 defaultを省略できる
18. ؔ࿈ػೳͷ੝Γ߹Θͤ 18 String result = switch (action) { case null -> "No action provided"; case Click(int x, int y) when x > 0 && y > 0 -> "Clicked at positive coordinates"; case Click(int x, int y) -> "Clicked at " + x + ", " + y; case Drag(int startX, int startY, int endX, int endY) -> "Dragged from " + startX + " to " + endX; case Scroll(int amount) when amount > 0 -> "Scrolled down by " + amount; case Scroll(int amount) when amount < 0 -> "Scrolled up by " + amount; case Scroll _ -> "No scrolling"; }; ガードパターンで 条件を追加できる 無名パターンで 変数が不要な時は 省略できる モデルの構造を変えずに 機能追加がしやすい nullの判定も できる
19. ύλʔϯϚονؔ࿈ػೳͷมભ ϓϨϏϡʔ ਖ਼ࣜϦϦʔε 19 TXJUDIࣜ JOTUBODFPG
    ύλʔϯϚον Ϩίʔυ γʔϧΫϥε TXJUDI
    ύλʔϯϚον Ϩίʔυ
    ύλʔϯ ແ໊ม਺
    ແ໊ύλʔϯ ϓϦϛςΟϒܕ
    ύλʔϯ                                   
20. ઴͘৽͘͠ೖΔ
    ػೳͷ࿩΁ 20
21. +BWB
    Ͱೖͬͨػೳ ϓϦϛςΟϒܕͰJOTUBODFPG΍TXJUDIΛ࢖ͬͨ
    ύλʔϯϚον͕Ͱ͖Δ 21
22. ϓϦϛςΟϒܕͷύλʔϯϚον 22 String result = switch (value) { case int i when i < 0 -> "Negative number: " + i; case 0 -> "Zero"; default -> "Positive number: " + value; }; return switch (year) { case int y when (y % 400 == 0) -> y + "೥͸Ӟ೥Ͱ͢"; case int y when (y % 100 == 0) -> y + "೥͸Ӟ೥Ͱ͸͋Γ·ͤΜ"; case int y when (y % 4 == 0) -> y + "೥͸Ӟ೥Ͱ͢"; };
23. কདྷɿؔ࿈͢Δ$BOEJEBUF +&1
    
    %FSJWFE
    3FDPSE
    $SFBUJPO
    1SFWJFX
    ϑΟʔϧυΛมߋͯ͠
    ϨίʔυΫϥεͷΠϯελϯεΛෳ੡Ͱ͖Δ 23
24. কདྷɿؔ࿈͢Δ$BOEJEBUF 24 record Point(int x, int y) { } Point oldLoc = new Point(1, 2); // x࠲ඪΛมߋͯ͠৽͍͠ϨίʔυΛ࡞੒ Point newLoc = oldLoc with { x = 0; }; // xͱy࠲ඪΛ2ഒʹͯ͠৽͍͠ϨίʔυΛ࡞੒ Point finalLoc = newLoc with { x *= 2; y *= 2; }; シンプルに書けるし Recordの イミュータブルな 特性をいかせる
25. ͓͞Β͍ • ύλʔϯϚονΛ׆༻ͯ͠ϘΠϥʔϓϨʔτ͕ݮΒͤՄಡੑ͕ ্͕Δ
    • ݱঢ়+BWBͷύλʔϯϚονͰ͸JOTUBODFPG΍TXJUDIΛ׆༻͢Δ
    • ܕΛ࢖ͬͯ҆શͳίʔυΛॻ͖΍͘͢ͳΔ
    • Ωϟετͷϛε͕ݮΒͤͨΓ
    • γʔϧΫϥεͰ࿙Εෆ଍͕ग़དྷͨΓ
    • ܕΛ׆༻͢Δ্ͰϨίʔυ͸͔ܽͤͳ͍ 25
26. 5IBOL
    ZPV 26