Javaの型とAI時代に型が大事な理由 / java types and type in AI era

+BWBͷܕͱɺ "*࣌୅ʹܕ͕େࣄͳཧ༝ +BWBͷܕΛʮ࢓༷ɾ੍໿ɾূ໌ʯͱͯ͠ཧղ͢Δ ܕ͸ɺਓؒɾ"*ɾίϯύΠϥͷڞ௨ݴޠ 1ZUIPO.FFUVQ'VLVPLB ͖ͩ͠ͳ͓͖

ࣗݾ঺հ ͖ͩ͠ ͳ͓͖ ʮϓϩʹͳΔ+BWBʯͱ͍͏+BWBͷຊΛॻ͍͍ͯ·͢ 9 5XJUUFS !LJT #MPH ͖ͩ͠ͷ)BUFOB 63-
OPXPLBZIBUFOBCMPHDPN

ಋೖ ࠓ೔ͷΰʔϧ +BWBͷجຊܕͱࢀরܕͷҧ͍Λཧղ͢Δ JEFOUJUZFRVBMJUZOVMMͷߟ͑ํΛཧղ͢Δ ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕΛʮܕʹΑΔ໿ଋʯͱͯ͠ཧղ͢Δ ૯শܕʴؔ਺Ͱࡾஈ࿦๏ͷϑϨʔϜΛݟΔ
"*࣌୅ʹܕ͕େࣄʹͳΔཧ༝Λઆ໌Ͱ͖ΔΑ͏ʹ͢Δ ಋೖ

ಋೖ "*࣌୅ʹɺͳͥܕͷ࿩Λ͢Δͷ͔ w "*͸ʮͦΕͬΆ͍ίʔυʯΛॻ͚Δ w ͔͠͠ʮͦΕͬΆ͍ʯͱʮਖ਼͍͠ʯ͸ҧ͏ w ܕ͸ɺίʔυͷதʹ੍໿ΛຒΊࠐΉํ๏ w ܕ͸ਓؒɾ"*ɾίϯύΠϥ͕ڞ༗Ͱ͖Δ࢓༷
ਓؒ ઃܭͷݴ༿ "* ै͏΂੍͖໿ ίϯύΠϥ͕ ݕࠪ͢Δϧʔϧ ܕ ಋೖ

ܕͷೖޱ ܕͱ͸Կ͔

ܕͷೖޱ 1ZUIPOʹ΋ܕ͸͋Δɻͨͩ͠࢖ΘΕํ͕ҧ͏ w 1ZUIPOͰ͸஋͕࣮ߦ࣌ͷܕΛ࣋ͭ w ܕΞϊςʔγϣϯ͸πʔϧ΍*%&͕׆༻͢Δ৘ใ w ඪ४ͷ࣮ߦ࣌Ͱ͸جຊతʹڧ੍͞Εͳ͍ w +BWBͰ͸ܕʹ߹Θͳ͍ίʔυ͸ίϯύΠϧͰࢭ·Δ
# Python def get_user_name(user_id: int) -> str: ... get_user_name("abc") # ࣮ߦ࣌ʹඞͣࢭ·Δͱ͸ݶΒͳ͍ // Java String name = "Alice"; name = 123; // ίϯύΠϧΤϥʔ ܕͷೖޱ

ܕͷೖޱ ܕͱ͸ʮ໿ଋʯͰ͋Δ w ͦͷ஋͕ԿͰ͋Δ͔ w ͦͷ஋ʹԿ͕Ͱ͖Δ͔ w ͦͷ஋ΛͲ͏ѻͬͯ͸͍͚ͳ͍͔ w ܕ͸ίϝϯτͰ͸ͳ͘ɺίϯύΠϥ͕ݕࠪͰ͖Δ໿ଋ
record UserId(String value) {} record EmailAddress(String value) {} void sendMail(EmailAddress email, MailTitle title, MailBody body) { ... } sendMail(title, email, body); // ίϯύΠϧΤϥʔ ܕͷೖޱ

+BWBͷܕͷجຊ جຊܕࢀরܕJEFOUJUZOVMM

+BWBͷܕͷجຊ +BWBͷܕ͸େ͖͘छྨ +BWBͷܕ جຊܕ QSJNJUJWFUZQF ࢀরܕ SFGFSFODFUZQF int / long
/ double / boolean ... String / LocalDate / User / int[] ... ஋ͦͷ΋ͷ ΦϒδΣΫτ΁ͷࢀর +BWBͷܕͷجຊ

+BWBͷܕͷجຊ جຊܕJEFOUJUZ͕ͳ͍஋ w छྨݻఆCZUFTIPSUJOUMPOHDIBSGMPBUEPVCMFCPPMFBO w ม਺͕஋ͦͷ΋ͷΛ࣋ͭ w OVMMʹͳΒͳ͍ w ಉ͡͸ɺͲ͜ʹ͋ͬͯ΋ಉ͡
int a = 3; int b = 3; System.out.println(a == b); // true +BWBͷܕͷجຊ

+BWBͷܕͷجຊ ࢀরܕΦϒδΣΫτ΁ͷࢀর w ม਺͸ΦϒδΣΫτͦͷ΋ͷͰ͸ͳ͘ࢀরΛ࣋ͭ w ΦϒδΣΫτʹ͸JEFOUJUZ͕͋Δ w ಺༰͕ಉ͡Ͱ΋ɺಉ͡ΦϒδΣΫτͱ͸ݶΒͳ͍ w ͲͷΦϒδΣΫτ΋ࢦ͍ͯ͠ͳ͍ঢ়ଶ͕OVMM
record Point(int x, int y) {} Point p1 = new Point(1, 2); Point p2 = new Point(1, 2); System.out.println(p1.equals(p2)); // true System.out.println(p1 == p2); // false +BWBͷܕͷجຊ

+BWBͷܕͷجຊ JEFOUJUZͱFRVBMJUZ JEFOUJUZ ಉ͡ݸମ͔ʁ FRVBMJUZ ಺༰ͱͯ͠౳͍͔͠ʁ ը໘"ͷʮొ࿥ʯϘλϯ ը໘#ͷʮొ࿥ʯϘλϯ ϥϕϧ͸ಉ͡Ͱ΋ผ෺
ಉ͡೔෇ͳΒಉ͡ҙຯ ΦϒδΣΫτʹ͸JEFOUJUZ͕͋Δɻ஋ʹ͸JEFOUJUZ͕ෆཁͳ͜ͱ͕ଟ͍ɻ +BWBͷܕͷجຊ

+BWBͷܕͷجຊ OVMMԿ΋ࢦ͍ͯ͠ͳ͍ࢀর w ࢀরܕ͸OVMMΛ࣋ͯΔ w جຊܕ͸OVMMʹͳΒͳ͍ w ܕͱͯ͠͸4USJOHͰ΋ɺ࣮ମ͕ͳ͍͜ͱ͕͋Δ w ܕ͸ڧྗ͕ͩɺOVMMͱ͍͏͕݀͋Δ
String name = null; System.out.println(name.length()); // NullPointerException int age = null; // ίϯύΠϧΤϥʔ +BWBͷܕͷجຊ

ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ ڞ௨ͷܕͱͯ͠ѻ͏ ܕΛύϥϝʔλʹ͢Δ

ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ ΫϥεͱΠϯλʔϑΣʔε w ΫϥεԿͰ͋Δ͔Ͳ͏࣮૷͞Ε͍ͯΔ͔ w ΠϯλʔϑΣʔεԿ͕Ͱ͖Δ͔ w ܕΛݟΔ͚ͩͰɺݺ΂Δૢ࡞͕෼͔Δ interface Animal
{ void speak(); } class Dog implements Animal { public void speak() { System.out.println("wan"); } } void speakTwice(Animal animal) { animal.speak(); animal.speak(); } ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ

ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ ଟ૬ܕ(͍ΘΏΔܧঝ)ڞ௨ͷܕͱͯ͠ѻ͏ w ͍͔ͭ͘ͷ۩ମܕΛڞ௨ͷܕͱͯ͠ѻ͏ w ಉ͡ݺͼग़͠Ͱ΋࣮ମʹΑͬͯಈ͖͕มΘΔ w ͦͷܕʹ͋Δૢ࡞͚ͩΛݺ΂Δ w "*ʹ΋ʮͰ͖Δ͜ͱ
Ͱ͖ͳ͍͜ͱʯΛࣔͤΔ Animal animal = new Dog(); animal.speak(); // wan animal = new Cat(); animal.speak(); // nya void process(Animal animal) { animal.fly(); // ίϯύΠϧΤϥʔ } ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ

ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ ૯শܕ(δΣωϦΫε)ܕΛύϥϝʔλʹ͢Δ w -JTU5ͷ 5͸ʮத਎ͷܕʯΛද͢ w -JTU4USJOH͸ 4USJOHͷϦετ w -JTU*OUFHFS͸
*OUFHFSͷϦετ w த਎ͷܕ·ͰίϯύΠϥ͕ݕࠪ͢Δ List<String> names = new ArrayList<>(); names.add("Alice"); // OK names.add(123); // ίϯύΠϧΤϥʔ String name = names.get(0); ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ

ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ ଟ૬ܕ WT૯শܕ w ଟ૬ܕ۩ମܕΛڞ௨ͷܕͱͯ͠ѻ͏ w ૯শܕܕͷҧ͍Λอͬͨ··ڞ௨Խ͢Δ w ଟ૬͸ʮͰ͖Δ͜ͱʯʹ஫໨͢Δ w
૯শܕ͸ʮܕͷରԠؔ܎ʯʹ஫໨͢Δ void makeSwim(Swimmable x) { x.swim(); } static <T> T first(List<T> xs) { return xs.get(0); } ΫϥεɾΠϯλʔϑΣʔεɾଟ૬ܕɾ૯শܕ

+BWBͷܕγεςϜͷͭΒ͍ͱ͜Ζ جຊܕͱࢀরܕͷ෼྾஋ͱΦϒδΣΫτ

+BWBͷͭΒ͍ͱ͜Ζ جຊܕͱࢀরܕ͕ผѻ͍ w AJOUA͸جຊܕɺA*OUFHFSA͸ࢀরܕ w ૯শܕʹجຊܕΛ௚઀࢖͑ͳ͍ w 4USFBN"1*Ͱ΋جຊܕ༻ͷಛผͳܕ͕͋Δ w ࣅͨ΋ͷΛɺผʑʹѻ͏ඞཁ͕͋Δ
List<int> xs; // ॻ͚ͳ͍ List<Integer> xs; // ͜͏ॻ͘ Stream<Integer> IntStream LongStream DoubleStream +BWBͷͭΒ͍ͱ͜Ζ

+BWBͷͭΒ͍ͱ͜Ζ جຊܕ͸ࣗ෼Ͱ࡞Εͳ͍ w جຊܕ͸छྨݻఆ w .POFZ6TFS*E&NBJM"EESFTT'MPBU͸جຊܕʹͰ͖ͳ͍ w ଟ͘ͷ৔߹ɺDMBTT΍SFDPSEͰදݱ͢Δ w υϝΠϯ্͸஋Ͱ΋ɺ+BWB্͸ΦϒδΣΫτʹͳΔ
record UserId(String value) {} record EmailAddress(String value) {} record Money(BigDecimal amount, Currency currency) {} +BWBͷͭΒ͍ͱ͜Ζ

+BWBͷͭΒ͍ͱ͜Ζ ஋͸ΦϒδΣΫτͰ͋Δඞཁ͕͋Δͷ͔ ೔෇ɾֹۚɾ࠲ඪɾϝʔϧΞυϨε JEFOUJUZ͸ຊ࣭Ͱ͸ͳ͍ ಉ͡஋ͳΒಉ͡ҙຯ Ϣʔβʔɾ஫จɾը໘্ͷϘλϯ JEFOUJUZ͕ॏཁ ಉ͡಺༰Ͱ΋ผݸମ +BWBͰ͸ɺ஋ͱͯ͠ѻ͍͍ͨ΋ͷ·Ͱ ΦϒδΣΫτͱͯ͠ද͢৔໘͕͋Δ
+BWBͷͭΒ͍ͱ͜Ζ 7BMIBMMBϓϩδΣΫτͰ౷ҰԽ͠Α͏ͱͯ͠Δ͚Ͳ ͳ͔ͳ͔׬੒͠ͳ͍ɾɾɾ

ܕͷϝϦοτ ؒҧͬͨ஋Λ౉ͤͳ͍࢓༷͕ίʔυʹ࢒Δ

ܕͷϝϦοτ ܕ͕͋ΔͱԿ͕͏Ε͍͠ͷ͔ w ؒҧͬͨ஋Λ౉ͤͳ͍ w ࢖͑Δૢ࡞͕෼͔Δ w ࢓༷͕ίʔυʹ࢒Δ w *%&ɾίϯύΠϥɾ"*͕ཧղ͠΍͍͢
w ϦϑΝΫλϦϯά͠΍͍͢ w ςετͷલʹόάΛ௵ͤΔόά͕͋Δ ܕͷϝϦοτ

ܕ͸ূ໌Ͱ͋Δ ૯শܕʴؔ਺Ͱࡾஈ࿦๏ͷϑϨʔϜΛݟΔ

ܕ͸ূ໌Ͱ͋Δ ܕΛ໋୊ɺ஋Λূڌͱͯ͠ݟΔ w ܕ"ͷ஋͕͋Δ"Ͱ͋Δূڌ͕͋Δ w 'VODUJPO" #"ͷূڌ͔Β#ͷূڌΛ࡞ΕΔ w ͭ·Γ'VODUJPO" #͸ʮ"ͳΒ͹#ʯ
w ͜ͷݟํ͕ʮܕ͸ূ໌ʯͷೖޱ Function<A, B> f; // A ͳΒ͹ B A a; // A Ͱ͋Δ B b = f.apply(a); // ͕ͨͬͯ͠ B Ͱ͋Δ ܕ͸ূ໌Ͱ͋Δ

ܕ͸ূ໌Ͱ͋Δ ڕɾࡪɾӭ͛ΔূڌܕͰද͢ w *T4BMNPOࡪͰ͋Δূڌ w *T'JTIڕͰ͋Δূڌ w $BO4XJNӭ͛Δূڌ record IsSalmon(String
name) {} record IsFish(String name) {} record CanSwim(String name) {} Function<IsSalmon, IsFish> salmonIsFish = s -> new IsFish(s.name()); Function<IsFish, CanSwim> fishCanSwim = f -> new CanSwim(f.name()); ܕ͸ূ໌Ͱ͋Δ

ܕ͸ূ໌Ͱ͋Δ ࡪͳΒڕɺڕͳΒӭ͛Δɺ͔ͩΒࡪ͸ӭ͛Δ w *T4BMNPO*T'JTI w *T'JTI$BO4XJN w *T4BMNPO$BO4XJNΛ DPNQPTFͰ࡞Δ w
ূڌΛͭͳ͛Δͷ͕ਪ࿦ Function<IsSalmon, CanSwim> salmonCanSwim = compose(salmonIsFish, fishCanSwim); CanSwim proof = salmonCanSwim.apply( new IsSalmon("αέ") ); ܕ͸ূ໌Ͱ͋Δ

ܕ͸ূ໌Ͱ͋Δ ͘͡Β͸ӭ͛ΔɻͰ΋ڕͱ͸ಋ͚ͳ͍ w *T8IBMF$BO4XJN͸͋Δ w *T'JTI$BO4XJN΋͋Δ w Ͱ΋ *T8IBMF*T'JTI͸࡞Εͳ͍ w
ʮӭ͛ΔͳΒڕʯͱ͍͏ϧʔϧ͸ͳ͍ record IsWhale(String name) {} Function<IsWhale, CanSwim> whaleCanSwim = w -> new CanSwim(w.name()); Function<IsFish, CanSwim> fishCanSwim = ...; // Function<IsWhale, IsFish> whaleIsFish = ? // ࡐྉ͕ͳ͍ͷͰಋ͚ͳ͍ ܕ͸ূ໌Ͱ͋Δ

ܕ͸ূ໌Ͱ͋Δ ૯শܕͰࡾஈ࿦๏ͷϑϨʔϜΛॻ͘ w "ͳΒ͹# w #ͳΒ͹$ w ͕ͨͬͯ͠"ͳΒ͹$ w ۩ମతͳܕʹґଘ͠ͳ͍ਪ࿦ύλʔϯ
static <A, B, C> Function<A, C> compose( Function<A, B> aToB, Function<B, C> bToC ) { return a -> bToC.apply(aToB.apply(a)); } ܕ͸ূ໌Ͱ͋Δ

ܕ͸ূ໌Ͱ͋Δ ܕ͕௨Δͱ͸Ͳ͏͍͏͜ͱ͔ w ܕͱͯ͠දݱ͞Εͨલఏ͔Βɺ w ܕͱͯ͠ڐ͞Εͨ݁࿦͚ͩΛಋ͍͍ͯΔ w ܕ͕௨Βͳ͍ ݁࿦Λಋͨ͘Ίͷূڌ͕଍Γͳ͍ w
*T8IBMF*T'JTI͸ূڌ͕ͳ͍ͷͰ࡞Εͳ͍ // ͋Δ: ͘͡Β -> ӭ͛Δ Function<IsWhale, CanSwim> whaleCanSwim; // ͋Δ: ڕ -> ӭ͛Δ Function<IsFish, CanSwim> fishCanSwim; // ͳ͍: ӭ͛Δ -> ڕ // ͔ͩΒ IsWhale -> IsFish ͸ಋ͚ͳ͍ ܕ͸ূ໌Ͱ͋Δ

ܕ͸ূ໌Ͱ͋Δ ͨͩ͠ɺܕ͚ͩͰ͢΂ͯ͸ূ໌Ͱ͖ͳ͍ w +BWBͷܕͰϓϩάϥϜͷਖ਼͠͞Λશ෦ূ໌Ͱ͖ΔΘ͚Ͱ͸ͳ͍ w AJOUEJWJEF JOUB JOUC A͸ܕͱͯ͠͸ਖ਼͍͠ w
͔͠͠C͸࣮ߦ࣌ʹ໰୊ʹͳΔ w ܕΛ޻෉͢ΔͱɺอূͰ͖ΔൣғΛ޿͛ΒΕΔ record NonZeroInt(int value) { public NonZeroInt { if (value == 0) { throw new IllegalArgumentException("zero"); } } } int divide(int a, NonZeroInt b) { return a / b.value(); } divide(10, 0); // ίϯύΠϧΤϥʔ ܕ͸ূ໌Ͱ͋Δ

"*࣌୅ʹܕ͕େࣄͳཧ༝ ܕ͸ϓϩϯϓτͰ͋Γɺ࠾఺ج४Ͱ͋Γɺ҆શ૷ஔͰ͋Δ

"*࣌୅ͷܕ ܕ͸"*΁ͷϓϩϯϓτͰ͋Δ w γάωνϟ͸ʮԿΛड͚औΓɺԿΛฦ͔͢ʯΛࣔ͢ w ۩ମతͳܕ΄Ͳɺ"*ʹ΋ਓؒʹ΋৘ใ͕ଟ͍ w 0CKFDUͩΒ͚ͷίʔυ͸ɺԿͰ΋Ͱ͖ͦ͏ͰԿ΋อূ͠ͳ͍ User register(EmailAddress
email, PlainPassword password) { ... } Object register(Object a, Object b) { ... } "*࣌୅ͷܕ

"*࣌୅ͷܕ ܕ͸"*ͷग़ྗΛ࠾఺͢Δج४Ͱ͋Δ "*͕ ίʔυΛॻ͘ ίϯύΠϥ͕ ܕΛݕࠪ ܕΤϥʔ͕ ग़Δ "*ਓ͕ؒ मਖ਼
ܕͷ໿ଋΛ ຬͨ͢ ܕ͕͋Δͱɺ"*ͷʮ΋ͬͱ΋Β͍ؒ͠ҧ͍ʯΛػցతʹམͱͤΔ ܕ͸ɺ"*Λ৴༻͢ΔͨΊͰ͸ͳ͘ɺ"*Λ৴༻͗͢͠ͳ͍ͨΊͷ҆શ૷ஔ "*࣌୅ͷܕ

"*࣌୅ͷܕ "*࣌୅ͷܕ࢓༷ɾ੍໿ɾূ໌ w ࢓༷ਓؒͱ"*͕ಡΉઃܭ৘ใ w ੍໿ؒҧͬͨ஋΍ૢ࡞Λڐ͞ͳ͍ڥք w ূ໌ܕͱͯ͠ڐ͞Εͨਪ࿦͚ͩΛ௨͢ w ʮԿͰ΋ॻ͚ΔʯΑΓʮؒҧͬͨ΋ͷΛॻ͚ͳ͍ʯ͕ॏཁ
"*࣌୅ͷܕ ΞϓϦέʔγϣϯͷߏ૝ΛܕͰදݱͰ͖ΔͷͰ͋Ε͹࣮ߦՄೳ

$MPTJOH ·ͱΊ +BWBͷܕ͸جຊܕͱࢀরܕʹେ͖͘෼͔ΕΔ JEFOUJUZFRVBMJUZOVMM͸+BWBͷܕཧղͷॏཁϙΠϯτ ଟ૬ܕ͸ڞ௨ͷܕͱͯ͠ѻ͍ɺ૯শܕ͸ܕΛอͬͯڞ௨Խ͢Δ ૯শܕʴؔ਺Ͱɺࡾஈ࿦๏ͷΑ͏ͳਪ࿦ϑϨʔϜΛදͤΔ
ܕ͸໋୊ɺ஋͸ূڌɺؔ਺ݺͼग़͠͸ਪ࿦ͱͯ͠ݟΒΕΔ "*࣌୅ʹ͸ɺܕ͸࢓༷ɾ੍໿ɾ࠾఺ج४ʹͳΔ "*͕ίʔυΛॻ࣌͘୅ʹ͸ɺʮؒҧͬͨ΋ͷΛॻ͚ͳ͍ʯઃܭ͕ॏཁʹͳΔɻ $MPTJOH

ܕ͸ɺ"*࣌୅ͷ҆શ૷ஔ ਓؒʹ͸ઃܭͷݴ༿ɺ"*ʹ͸ै͏΂͖࢓༷ɺίϯύΠϥʹ͸ݕࠪͰ͖Δϧʔϧɻ

Javaの型とAI時代に型が大事な理由 / java types and type in AI...

Javaの型とAI時代に型が大事な理由 / java types and type in AI era

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