今こそ、ラムダ式を考える - なぜあなたはラムダ式を苦手と感じるのか

Burikaigi ブリ会議 2024
発表資料

Java, Java SE, Project Lambda, ラムダ式, Lambda Expression
関数型プログラミング

1. ࠓͦ͜ɺϥϜμࣜΛߟ͑Δ ᓎఉ
   ༞Ұ Java in the Box ͳͥ͋ͳͨ͸ϥϜμࣜΛۤखͱײ͡Δͷ͔
2. ϥϜμࣜಋೖ Java 8ϦϦʔε 2014: ؔ਺ܕϓϩάϥϛϯάػೳͷ୺ॹ
3. ϥϜμࣜಋೖ Java 8ϦϦʔε 2014: ؔ਺ܕϓϩάϥϛϯάػೳͷ୺ॹ Records Sealed Class Pattern Matching ݴޠ࢓༷ ୅਺తσʔλܕ ^ ඪ४ϥΠϒϥϦ Stream API CompletableFuture Flow (Reactive Stream) HTTP Client ϑϨʔϜϫʔΫ Spring WebFlux Oracle Helidon Red Hat Quarkus et al.
4. ϥϜμࣜಋೖ Java 8ϦϦʔε 2014: ؔ਺ܕϓϩάϥϛϯάػೳͷ୺ॹ Records Sealed Class Pattern Matching ݴޠ࢓༷ ୅਺తσʔλܕ ^ ඪ४ϥΠϒϥϦ Stream API CompletableFuture Flow (Reactive Stream) HTTP Client ϑϨʔϜϫʔΫ Spring WebFlux Oracle Helidon Red Hat Quarkus et al. ΋ؔ਺ܕϓϩάϥϛϯά͔ΒಀΕΒΕͳ͍ Java खଓ͖ܕ
   ͔Β
   એݴܕ
   ΁ จ
   ͔Β
   ࣜ
   ΁ ϥϜμࣜಋೖ͔Β೥ ͋ΒͨΊͯϥϜμࣜΛݟ௚ͯ͠ΈΔ ϥϜμࣜΛ࢖͏ ϥϜμࣜͷಈ࡞Λཧղ͢Δ
5. ϥϜμࣜ
   
   
   
   ແ໊ ؔ਺ ࢖͏্Ͱ͸
6. ϥϜμࣜ
   
   
   
   ແ໊ ؔ਺ ࢖͏্Ͱ͸ ϝιου͕ॻ͚Δ
   
   
   
   
   
   ϥϜμࣜ΋ॻ͚Δ JLS 15.27 A lambda expression is like a method ॻ͖ํͷ໰୊Ͱ͸ͳ͘ɺߟ͑ํͷ໰୊ खଓ͖తهड़ͷढറ ͍ʹ͑͠ͷ Java ͷهड़ελΠϧ΁ͷݻࣥ
7. มԽʹ͸ඞͣίετ͕൐͍·͢ Brian Goetz Project Lambdaͷల๬ Java Magazine Oct. 2012
8. खଓ͖తهड़ͷ໰୊఺ ෳ਺ͷॲཧΛҰॹʹ͔͚ͯ͠·͏ ϛϡʔλϒϧม਺ͷଟ༻ ม਺ͷείʔϓ͕޿͘ͳΓ͕ͪ
9. record StudentScore(String name, String className, int score) {} List<StudentScore> scores = ...; ྫ
   "૊ͷੜెͷฏۉࢉग़ record StudentScore(String name, String className, int score) {} List<StudentScore> scores = ...; double sum = 0.0; int count = 0; for (int i = 0; i < scores.size(); i++) { var ss = scores.get(i); if (ss.className().equals("A")) { sum += ss.score(); count++; } } sum /= count; தؒঢ়ଶอ࣋ͷͨΊϛϡʔλϒϧ είʔϓ͕޿͍ ϧʔϓ੍ޚ ஋औग़ɺ ৚݅ Ճࢉॲཧ͕ҰମԽ ҙຯͷҟͳΔ஋ͷ୅ೖ
10. record StudentScore(String name, String className, int score) {} List<StudentScore> scores = ...; final double ave = scores.stream() .filter(ss -> ss.className().equals("A")) .collect(Collectors.averagingDouble( ss -> ss.scores() )); ஋औग़ ৚݅ Πϛϡʔλϒϧม਺ ฏۉ஋ࢉग़
11. ϥϜμࣜ
    
    
    
    ແ໊ ؔ਺ ࢖͏্Ͱ͸ Ϋϥεʹ͸ଐ͞ͳ͍ ୯ମͰॲཧ͚ͩهड़͢Δ
12. ϥϜμࣜͷܕ͸ؾʹ͠ͳ͍ List<Integer> nums = ...; var sortedNums = nums.stream() .sorted( (x1, x2) -> x1-x2 ) .toList(); ྫ
    Ϧετͷιʔτ ͜ͷϥϜμࣜͷܕ͕ Comparatorͳͷ͔ BiFunction ͳͷ͔ ߟ͑Δඞཁ͸ͳ͍ ॏཁͳͷ͸  Ҿ਺Ͱൺֱ݁ՌΛ JOU Ͱฦ͢ͱ͍͏͜ͱ
13. ϥϜμࣜͰॏཁͳͷ͸γάωνϟʔ Ҿ਺ͷݸ਺ܕ ໭Γ஋ͷ༗ແܕ List<Integer> nums = ...; var sortedNums = nums.stream() .sorted( (x1, x2) -> x1-x2 ) .toList(); Ҿ਺ݸ਺ 
    
     Ҿ਺ܕ 
    
    Integer, Integer ໭Γ஋ 
    
    ͋Γ ໭Γ஋ܕ 
    
    Integer
14. ϥϜμࣜͰॏཁͳͷ͸γάωνϟʔ java.util.functionͷؔ਺ܕΠϯλϑΣʔε͸ γάωνϟʔΛ۠ผ͢ΔͨΊͷ΋ͷ Ҿ਺ͳ͠ Ҿ਺
    
    
    
    Ҿ਺
     Ҿ਺
     ໭Γ஋͋Γ ໭Γ஋͋Γ ໭Γ஋
    boolean ໭Γ஋ͳ͠ Supplier<T> Function<T, R> Predicate<T> Consumer<T>
15. ϥϜμࣜΛॻ͘ʹ͸ ϥϜμ͚ࣜͩͰߟ͑ͣɺ ϥΠϒϥϦͱڞʹ ϥϜμ͕ࣜҾ਺ɺ ໭Γ஋ͱͳΔߴ֊ؔ਺Ͱͷར༻͕΄ͱΜͲ Project Lambda͸୯ͳΔݴޠػೳͰ͸ͳ͘ɺ ϥΠϒϥϦ΋ର৅ͱ͍ͯ͠·͢ɻ ݴޠػೳͱϥΠϒϥϦ͕Ұମͱͳͬͯɺ Javaϓϩάϥϛϯά ɾ ϞσϧΛେ෯ʹ ΞοϓάϨʔυ͠·͢ɻ Brian Goetz Project Lambdaͷల๬ Java Magazine Oct. 2012
16. ϥϜμࣜΛॻ͘ʹ͸ ϥϜμ͚ࣜͩͰߟ͑ͣɺ ϥΠϒϥϦͱڞʹ ϥϜμ͕ࣜҾ਺ɺ ໭Γ஋ͱͳΔߴ֊ؔ਺Ͱͷར༻͕΄ͱΜͲ ॲཧ͸͚ͭͩ ॲཧ͕ෳ਺͋Ε͹ɺ ෳ਺ͷϥϜμࣜʹ෼ׂ ॲཧʹ࢖༻͢Δσʔλ͸Ҿ਺͚ͩʹ͢Δ ϥϜμࣜͷ֎ଆͷσʔλʹ͸Ͱ͖Δ͚ͩΞΫηε͠ͳ͍ ॲཧ݁ՌΛ໭Γ஋Ҏ֎Ͱ໭͞ͳ͍ ม਺͸Πϛϡʔλϒϧʹ͢Δ
17. ·ͱΊ ϥϜμࣜ͸ ແ໊ ؔ਺ +BWBͰ΋એݴతهड़͕૿Ճத ϥϜμࣜͷۤखҙࣝΛͳ͘͢ʹ͸
    
    
    
    
    
    
    
    
    खଓ͖తࢥߟ͔Βͷ୤٫͕ඞཁ ࢀߟ
    ͳͬͱ͘
    ؔ਺ܕϓϩάϥϛϯά
    
    
    
    
    
    
    
    Michał Płachta