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Intro to typeclass in Scala

Intro to typeclass in Scala

Kazuhiro Ichikawa

June 28, 2019
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  1. *OUSPUPUZQFDMBTTJO4DBMB
    4DBMBʹ͓͚ΔܕΫϥεೖ໳
    'JWF*OD
    !QIFOBO

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  2. ໨࣍
    $POUFOUT
    6OEFSTUBOEJOHUZQFDMBTTFT
    6TJOHUZQFDMBTTFTJO4DBMB
    6TJOHUZQFDMBTTFTJO4DBMB
    ͜͜ʹ೔ຊޠࣈນ͕ೖΓ·͢

    View full-size slide

  3. 6OEFSTUBOEJOHUZQFDMBTTFT
    ܕΫϥεΛཧղ͠Α͏

    View full-size slide

  4. ܕΫϥε
    5ZQFDMBTT
    w -BOHVBHFDPOTUSVDUUIBUTVQQPSUTBEIPDQPMZNPSQIJTN
    w "EIPDQPMZNPSQIJTN
    w "LJOEPGQPMZNPSQIJTNUIBUBMMPXTEFDMBSJOHGVODUJPOTUIBU
    DBOCFBQQMJFEGPSBSHVNFOUTPGEJGGFSFOUUZQFT
    w *UJTLOPXOBTPWFSMPBEJOH
    w 0,4P 8IBUJTUZQFDMBTT
    ܕΫϥεͬͯԿ ΞυϗοΫϙϦϞʔϑΟζϜͬͯԿ
    Φʔόʔϩʔυ ݁ہͲ͏͍͏͜ͱ

    View full-size slide

  5. ετϥςδύλʔϯ
    4USBUFHZQBUUFSO
    w 0OFPGBEFTJHOQBUUFSOJOUSPEVDFECZ(P'
    w 3FHBSETBQJFDFPGMPHJDBTBOPCKFDU DBMMFETUSBUFHZ

    w &OBCMFTTFMFDUJOHTVJUBCMFTUSBUFHZBUSVOUJNF
    ετϥςδύλʔϯ

    ϩδοΫͷҰ෦ΛΦϒδΣΫτʹͯ͠੾Γସ͑Մೳʹ͢Δ

    View full-size slide

  6. ετϥςδύλʔϯ
    4USBUFHZQBUUFSO
    SVOͷϩδοΫΛ4USBUFHZΦϒδΣΫτʹ෼཭͠ɺ
    4USBUFHZΛ౉͔͢4USBUFHZΛ౉͔͢ͰॲཧΛ෼͚Δ
    interface/trait
    Strategy
    abstract logic()
    object
    Strategy2
    def logic()
    object
    Strategy1
    def logic()
    def run(strategy:Strategy) = {

    strategy.logic()

    }
    DBMM

    run(Strategy1)

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  7. ۩ମྫίϯύϨʔλ
    &YBNQMF$PNQBSBUPS
    Α͘ར༻͞ΕΔ۩ମྫ͸$PNQBSBUPSͰɺ

    TPSU಺෦Ͱར༻͢Δൺֱؔ਺Λ֎͔Βม͑ΒΕΔ
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }

    sort(list, 

    IntComparator)

    DBMM

    View full-size slide

  8. ۩ମྫίϯύϨʔλ
    &YBNQMF$PNQBSBUPS
    4DBMBͰͷ࣮૷ྫ
    trait Comparator[T] {
    def compare(a: T, b: T): Int
    }
    object IntComparator extends Comparator[Int] {
    def compare(a: Int, b: Int): Int = a - b
    }
    def sort[T](list: List[T], comparator: Comparator[T]): List[T] = {
    list match {
    case x :: xs =>
    val (ys, zs) = xs.partition(a => comparator.compare(x, a) > 0)
    sort(ys, comparator) ++ List(x) ++ sort(zs, comparator)
    case Nil => Nil
    }
    }
    sort(List(6, 1, 4, 7, 5, 2, 9, 3, 8), IntComparator)

    View full-size slide

  9. ετϥςδ͸େ఍ͷ৔߹ࣗ໌Ͱ͋Δ
    4USBUFHZJTPCWJPVTJONPTUDBTFT
    w *ONPTUDBTFT XFVTFlOBUVSBMzPSEFSGPSDPNQBSJOHWBMVFT
    w OVNFSJDBMPSEFSGPSJOUFHFSWBMVFT
    w DISPOPMPHJDBMPSEFSGPSEBUFWBMVFT
    w /PUFUIBUlOBUVSBMzPSEFSJTEJGGFSFOUCFUXFFOEJGGFSFOUUZQFT
    w 0CWJPVTTUSBUFHZDBOCFJOGFSSFEGSPNTUBUJDUZQF
    ܕʹΑͬͯzࣗવͳzετϥςδ͕͋Γɺ

    େ఍͸ͦΕΛ࢖͑͹ྑ͍

    View full-size slide

  10. ܕΫϥε㲈ܕγεςϜʹΑΓࢧԉ͞Εͨετϥςδύλʔϯ
    5ZQFDMBTT㲔TUSBUFHZQBUUFSOBTTJTUFECZUZQFTZTUFN
    w 5ZQFTZTUFNBVUPNBUJDBMMZTFBSDIFTTVJUBCMFTUSBUFHZ
    w 1SPHSBNNFSTEPOPUOFFEUPTQFDJGZTUSBUFHZ
    w 1SPHSBNNFSTDBOEFDMBSFlOBUVSBMzTUSBUFHZGPSBOZUZQF
    ܕΫϥε͸ཁ͸ετϥςδύλʔϯ
    ετϥςδΛܕ͔ΒࣗಈͰܾΊΔ࢓૊Έ͕͋Ε͹ྑ͍

    View full-size slide

  11. ܕΫϥεͱܕΫϥεΠϯελϯε
    5ZQFDMBTTBOEUZQFDMBTTJOTUBODF
    w 5ZQFDMBTTJTBTUSBUFHZJOUFSGBDF PSUSBJU

    w l9JTJOTUBODFPGUZQFDMBTT5zNFBOT

    lTUSBUFHZPCKFDUPGUZQF5<9>FYJTUTz
    9͕ܕΫϥε5ͷΠϯελϯεͰ͋Δͱ͸ɺ
    5<9>ܕͷετϥςδΦϒδΣΫτ͕࣮૷Ͱ͖Δ͜ͱΛࢦ͢

    View full-size slide

  12. ܕΫϥεͱܕΫϥεΠϯελϯε
    5ZQFDMBTTBOEUZQFDMBTTJOTUBODF
    ͭ·Γ
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM

    sort(list, 

    IntComparator)

    View full-size slide

  13. ܕΫϥεͱܕΫϥεΠϯελϯε
    5ZQFDMBTTBOEUZQFDMBTTJOTUBODF
    ͕͜͜ܕΫϥε
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM
    5ZQFDMBTT

    sort(list, 

    IntComparator)

    View full-size slide

  14. ܕΫϥεͱܕΫϥεΠϯελϯε
    5ZQFDMBTTBOEUZQFDMBTTJOTUBODF
    *OU$PNQBSBUPS͸$PNQBSBUPS<*OU>Λ࣮૷͍ͯ͠ΔͷͰ
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM
    $PNQBSBUPS<*OU>
    5ZQFDMBTT

    sort(list, 

    IntComparator)

    View full-size slide

  15. ܕΫϥεͱܕΫϥεΠϯελϯε
    5ZQFDMBTTBOEUZQFDMBTTJOTUBODF
    *OU͸ܕΫϥε$PNQBSBUPSͷΠϯελϯεͰ͋Δͱ͍͏
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM
    5ZQFDMBTT
    *OUJTJOTUBODFPG
    $PNQBSBUPS
    $PNQBSBUPS<*OU>

    sort(list, 

    IntComparator)

    View full-size slide

  16. ܕΫϥε੍໿
    5ZQFDMBTTDPOTUSBJOU
    w 5ZQFDMBTTDPOTUSBJOUJTBQBSBNFUFSUIBUUBLFTTUSBUFHZ
    ܕΫϥε੍໿ͱ͸ετϥςδΛͱΔҾ਺Λࢦ͢

    View full-size slide

  17. ܕΫϥε੍໿
    5ZQFDMBTTDPOTUSBJOU
    ͭ·Γ
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM
    5ZQFDMBTT
    *OUJTJOTUBODFPG
    $PNQBSBUPS
    $PNQBSBUPS<*OU>

    sort(list, 

    IntComparator)

    View full-size slide

  18. ܕΫϥε੍໿
    5ZQFDMBTTDPOTUSBJOU
    TPSUͷ$PNQBSBUPS<5>ܕͷҾ਺͸ܕΫϥε੍໿
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM
    5ZQFDMBTT
    5ZQFDMBTTDPOTUSBJOU
    *OUJTJOTUBODFPG
    $PNQBSBUPS
    $PNQBSBUPS<*OU>

    sort(list, 

    IntComparator)

    View full-size slide

  19. ܕΫϥεͷΠϯελϯεએݴ
    5ZQFDMBTTJOTUBODFEFDMBSBUJPO
    w *OTUBODFEFDMBSBUJPOEFDMBSFTlOBUVSBMzTUSBUFHZUPUZQF
    TZTUFN
    w 5IJTNFBOTUIBUUZQFTZTUFNBVUPNBUJDBMMZVTFTJUGPS
    BSHVNFOUPGUZQFDMBTTDPOTUSBJOU
    ܕγεςϜ͕zࣗવͳzετϥςδΛݟ͚ͭΒΕΔΑ͏ʹɺ

    Πϯελϯεએݴͱ͍͏΋ͷ͕ඞཁ

    View full-size slide

  20. ܕΫϥεͷΠϯελϯεએݴ
    5ZQFDMBTTJOTUBODFEFDMBSBUJPO
    ͭ·Γ
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM
    5ZQFDMBTT
    5ZQFDMBTTDPOTUSBJOU
    *OUJTJOTUBODFPG
    $PNQBSBUPS
    $PNQBSBUPS<*OU>

    sort(list, 

    IntComparator)

    View full-size slide

  21. ܕΫϥεͷΠϯελϯεએݴ
    5ZQFDMBTTJOTUBODFEFDMBSBUJPO
    *OU$PNQBSBUPS͕$PNQBSBUPS<*OU>ͷzࣗવͳz࣮૷Ͱ͋
    Δͱએݴ͢Δͱ Πϯελϯεએݴ

    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }
    DBMM
    5ZQFDMBTT
    5ZQFDMBTTDPOTUSBJOU
    %FDMBSFIntComparatorJTOBUVSBMTUSBUFHZ

    GPSComparator[Int]

    sort(list, 

    IntComparator)

    View full-size slide

  22. ܕΫϥεͷΠϯελϯεએݴ
    5ZQFDMBTTJOTUBODFEFDMBSBUJPO
    TPSUͷҾ਺ʹετϥςδΛ༩͑ͳ͘ͱ΋ܕγεςϜ͕ࣗಈ
    Ͱ*OU$PNQBSBUPSΛ୳ͯ͠౉ͯ͘͠ΕΔ
    interface/trait
    Comparator[T]
    abstract
    compare(a: T, b: T)
    object
    DateComparator
    def compare

    (a: Date, b: Date)
    object
    IntComparator
    def compare

    (a: Int, b: Int)
    def sort[T]

    (list:List[T])

    (cmp:Comparator[T]) = {

    cmp.compare(…)

    }

    sort(list)

    DBMM
    5ZQFDMBTT
    5ZQFDMBTTDPOTUSBJOU
    5ZQFTZTUFNBVUPNBUJDBMMZ
    SFTPMWFTUZQFDMBTT

    View full-size slide

  23. ·ͱΊ
    4FDUJPOTVNNBSZ
    w 5ZQFDMBTT㲔TUSBUFHZJOUFSGBDF
    w l9JTJOTUBODFPGUZQFDMBTT5zNFBOT

    lTUSBUFHZPCKFDUPGUZQF5<9>FYJTUTz
    w 5ZQFDMBTTDPOTUSBJOU㲔TUSBUFHZQBSBNFUFS
    w 5ZQFDMBTTJOTUBODFEFDMBSBUJPOEFDMBSFTlOBUVSBMzTUSBUFHZ
    ܕΫϥε͸ετϥςδύλʔϯͰཧղͰ͖Δ

    View full-size slide

  24. 6TJOHUZQFDMBTTFTJO4DBMB
    4DBMBͰܕΫϥεΛ࢖͏

    View full-size slide

  25. ܕΫϥεͷએݴ
    5ZQFDMBTTEFDMBSBUJPO
    w *O4DBMB UZQFDMBTTJTEFDMBSFEBTBUSBJU
    ܕΫϥε͸ҰൠʹUSBJUͱͯ͠એݴ͢Δ
    trait Comparator[T] {
    def compare(a: T, b: T): Int
    }

    View full-size slide

  26. ετϥςδΦϒδΣΫτ
    4USBUFHZPCKFDU
    w "OPCKFDUJNQMFNFOUJOHUIFUSBJUPGUZQFDMBTT
    w 'PMMPXJOHDPEFNFBOTIntJTJOTUBODFPGComparator
    $PNQBSBUPS<*OU>ͷ࣮૷
    ͜Ε͕࣮૷Ͱ͖ΔͷͰ*OU͸$PNQBSBUPSͷΠϯελϯε
    object IntComparator extends Comparator[Int] {
    def compare(a: Int, b: Int): Int = a - b
    }

    View full-size slide

  27. ܕΫϥεΠϯελϯεએݴ
    5ZQFDMBTTJOTUBODFEFDMBSBUJPO
    w “implicit object”JTUZQFDMBTTJOTUBODFEFDMBSBUJPO
    w 8FDBOEFGJOF“implicit object”POMZXJUIJODMBTTPSPCKFDU
    EFDMBSBUJPO
    ΠϯελϯεએݴΛ͢Δʹ͸JNQMJDJUPCKFDUΛ࢖͏
    object Comparators {
    implicit object IntComparator extends Comparator[Int] {
    def compare(a: Int, b: Int): Int = a - b
    }
    }

    View full-size slide

  28. ܕΫϥε੍໿
    5ZQFDMBTTDPOTUSBJOU
    w *O4DBMB QBSBNFUFSXJUI“implicit”LFZXPSEFYQSFTTFT
    UZQFDMBTTDPOTUSBJOU
    w "SHVNFOUPGJNQMJDJUQBSBNFUFSJTBVUPNBUJDBMMZTFBSDIFE
    GSPNEFDMBSFEJNQMJDJUWBMVFTJOTDPQF
    ܕΫϥε੍໿͸JNQMJDJUύϥϝʔλͰදݱ͢Δ
    def sort[T](list: List[T])(implicit cmp: Comparator[T]): List[T] = {
    list match {
    case x :: xs =>
    val (ys, zs) = xs.partition(a => cmp.compare(x, a) > 0)
    sort(ys) ++ List(x) ++ sort(zs)
    case Nil => Nil
    }
    }

    View full-size slide

  29. ܕΫϥε੍໿Λ࣋ͭؔ਺ͷ࢖͍ํ
    6TBHFPGGVODUJPOXJUIUZQFDMBTTDPOTUSBJOU
    w 8FDBOVTFsortGVODUJPOXJUIPVUTQFDJGZJOHDPNQBSBUPSBT
    JUTBSHVNFOU
    w 8FTIPVMEJNQPSUComparatorsGPSFOBCMJOHJOTUBODFEFDMT
    JNQMJDJUύϥϝʔλ͸ܕγεςϜ͕ࣗಈͰຒΊͯ͘ΕΔ

    ΠϯελϯεએݴΛJNQPSU͓ͯ͘͠ඞཁ͕͋Δ
    import Comparators._
    sort(List(1, 3, 2))
    sort(List(“a”, “c”, “b”)) // error: Comparator[String] not found

    View full-size slide

  30. Πϯελϯεએݴͷଞͷํ๏
    "OPUIFSXBZPGJOTUBODFEFDMBSBUJPO
    w “implicit def”XJUIOPQBSBNFUFSJTBMTPJOTUBODFEFDMBSBUJPO
    w 5IJTJTVTFEGPSEFDMBSJOHJOTUBODFXJUIHFOFSJDUZQF
    ܕҾ਺Λ࣋ͭܕͷΠϯελϯεએݴ͸JNQMJDJUEFGͰߦ͏
    object Comparators {
    implicit def setSizeComparator[T]: Comparator[Set[T]] = {

    new Comparator[Set[T]] {
    def compare(a: Set[T], b: Set[T]): Int = a.size - b.size
    }
    }
    }
    Note: This comparator is not common for set.

    View full-size slide

  31. Πϯελϯεએݴͷଞͷํ๏
    "OPUIFSXBZPGJOTUBODFEFDMBSBUJPO
    w *OTUBODFEFDMBSBUJPODBOIBWFUZQFDMBTTDPOTUSBJOU
    JNQMJDJUEFG΋ܕΫϥε੍໿Λ࣋ͭ͜ͱ͕Ͱ͖ɺ

    ͜ΕʹΑΓෳࡶͳܕͷΠϯελϯεએݴ͕Ͱ͖Δ
    object Comparators {
    implicit def tupleComparator[T1, T2]
    (implicit cmp1: Comparator[T1],
    cmp2: Comparator[T2]): Comparator[(T1, T2)] = {

    new Comparator[(T1, T2)] {
    def compare(a: (T1, T2), b: (T1, T2)): Int = {
    val res1 = cmp1.compare(a._1, b._1)
    if (res1 == 0) cmp2.compare(a._2, b._2)
    else res1
    }
    }
    }
    }

    View full-size slide

  32. ܕΫϥεͷϝιουͷ࢖͍ํ
    6TJOHNFUIPEPGUZQFDMBTT
    w 5PJOWPLFcompareNFUIPE XFOFFE$PNQBSBUPSJOTUBODF
    w 8FDBOPCUBJOUZQFDMBTTJOTUBODFCZimplicitlyNFUIPE
    ܕΫϥεͷϝιουΛݺͿʹ͸ܕΫϥεΠϯελϯε͕ඞཁ
    JNQMJDJUMZͰܕΫϥεΠϯελϯεΛऔಘͰ͖Δ
    import Comparators._
    IntComparator.compare(1, 2)
    implicitly[Comparator[(Int, Int)]].compare((1, 2),(3, 4))

    View full-size slide

  33. JNQMJDJUMZ<ʜ>DPNQBSF B C
    JTOPUJOUVJUJWF
    w 8FXBOUUPXSJUF“a > b”SBUIFSUIBO“….compare(a, b) > 0”
    w 8FEPOPUXBOUUPFYQMJDJUMZXSJUFUZQFDMBTTJOTUBODF
    ܕΫϥεΠϯελϯεΛ໌ࣔతʹॻ͖ͨ͘ͳ͍ʂ
    import Comparators._
    if (implicitly[Comparator[(Int, Int)]].compare((1, 2),(3, 4)) > 0) {

    }
    if ((1, 2) > (3, 4)) {

    }
    ௚ײతʹ෼͔ΓͮΒ͍

    View full-size slide

  34. ܕΫϥεΠϯελϯεͷͨΊͷ֦ுϝιου
    &YUFOTJPONFUIPETGPSUZQFDMBTTJOTUBODFT
    w 8FDBOEFDMBSFFYUFOTJPONFUIPECZ“implicit class”
    w “implicit class”DBOBMTPUBLFTUZQFDMBTTDPOTUSBJOU
    JNQMJDJUDMBTTͰطଘΫϥεʹϝιουΛੜ΍ͤΔ
    ܕ੍໿Λ͚ͭΕ͹ܕΫϥεΠϯελϯεͰͷΈ࢖͑ΔΑ͏ʹ
    object ComparatorSyntax {
    implicit class ComparatorOps[T](a: T)
    (implicit cmp: Comparator[T]) {

    def > (b: T): Boolean = cmp.compare(a, b) > 0
    }
    }
    import Comparators._
    import ComparatorSyntax._
    (1, 2) > (2, 4) // return false

    View full-size slide

  35. 4DBMBʹ͓͚ΔJNQMJDJUͷҙຯ
    *NQMJDJUTJO4DBMB
    4DBMBͰ͸༷ʑͳҙຯͰJNQMJDJU͕࢖ΘΕ͍ͯΔ
    no parameters one parameter implicit
    parameters
    implicit
    parameter
    typeclass
    constraint - -
    implicit val
    implicit object
    instance
    declaration - -
    implicit class Error!
    extension
    methods ○
    implicit def instance
    declaration
    implicit
    conversion

    View full-size slide

  36. 4DBMBͷܕΫϥεϥΠϒϥϦ
    5ZQFDMBTTMJCSBSJFTJO4DBMB
    w 5IFSFBSFUXPNBKPSMJCSBSJFT
    w 4DBMB[
    w $BUT
    w 5IJTTMJEFCSJFGMZEFTDSJCFTQBDLBHFTUSVDUVSFPGUIFN
    w 6TFSTOFFEUPJNQPSUUZQFDMBTTFT JOTUBODFEFDMBSBUJPOT
    BOEFYUFOTJPONFUIPETGPSVTJOHUIFTFMJCTXFMM
    ೋେܕΫϥεϥΠϒϥϦ4DBMB[ $BUT
    ͜ΕΒΛ্ख͘࢖͏ʹ͸ύοέʔδߏ଄Λ஌͓ͬͯ͘ඞཁ

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  37. 4DBMB[ͷύοέʔδߏ੒
    1BDLBHFTUSVDUVSFPG4DBMB[
    w TDBMB[
    w UZQFDMBTTEFDMBSBUJPOT
    w TDBMB[TUE
    w JOTUBODFEFDMBSBUJPOTPGDPNNPOUZQFT
    w TDBMB[TZOUBY
    w FYUFOTJPONFUIPET
    TDBMB[TUEҎԼʹΠϯελϯεએݴ
    TDBMB[TZOUBYҎԼʹ֦ுϝιου͕ఆٛ͞Ε͍ͯΔ

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  38. $BUTͷύοέʔδߏ੒
    1BDLBHFTUSVDUVSFPG$BUT
    w DBUT
    w UZQFDMBTTEFDMBSBUJPOT
    w DBUTJOTUBODFT
    w JOTUBODFEFDMBSBUJPOTPGDPNNPOUZQFT
    w DBUTTZOUBY
    w FYUFOTJPONFUIPET
    $BUT΋ࣅͨΑ͏ͳύοέʔδͷߏ଄Λ͍ͯ͠Δ

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  39. 6TJOHUZQFDMBTTFTJO4DBMB
    4DBMBͰܕΫϥεΛ࢖͏

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  40. 4DBMBʹ͓͚ΔܕΫϥεએݴ
    5ZQFDMBTTEFDMBSBUJPOJO4DBMB
    w 5ZQFDMBTTJTEFDMBSFEBTBUSBJU
    4DBMBͱಉ༷ʹܕΫϥεͷએݴ͸USBJU
    trait Comparator[T] {
    def compare(a: T, b: T): Int
    }

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  41. 4DBMBʹ͓͚ΔܕΫϥεΠϯελϯεએݴ
    5ZQFDMBTTJOTUBODFEFDMBSBUJPOJO4DBMB
    • “delegate for”JTJOTUBODFEFDMBSBUJPO
    • 5IFOBNFPGEFMFHBUFJOTUBODFJTPQUJPOBM
    Πϯελϯεએݴ͸৽ͨʹEFMFHBUFGPSߏจ͕ಋೖ
    object Comparators {
    delegate IntComparator for Comparator[Int] {
    def compare(a: Int, b: Int): Int = a - b
    }
    delegate [T] for Comparator[Set[T]] {
    def compare(a: Set[T], b: Set[T]): Int = a.size - b.size
    }
    }

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  42. 4DBMBʹ͓͚ΔܕΫϥε੍໿ͷॻ͖ํ
    5ZQFDMBTTDPOTUSBJOUJO4DBMB
    w *O4DBMB QBSBNFUFSMJTUGPMMPXJOH“given”LFZXPSEFYQSFTTFT
    UZQFDMBTTDPOTUSBJOU
    ܕΫϥε੍໿͸HJWFOΩʔϫʔυͰએݴ͢Δ
    def sort[T](list: List[T]) given (cmp: Comparator[T]): List[T] = {
    list match {
    case x :: xs =>
    val (ys, zs) = xs.partition(a => cmp.compare(x, a) > 0)
    sort(ys) ++ List(x) ++ sort(zs)
    case Nil => Nil
    }
    }

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  43. ܕΫϥε੍໿Λ࣋ͭؔ਺ͷ࢖͍ํ
    6TBHFPGGVODUJPOXJUIUZQFDMBTTDPOTUSBJOU
    w 8FTIPVMEJNQPSUJOTUBODFEFDMBSBUJPOTCZ“import delegate”
    w 8FDBOFYQMJDJUMZHJWFBOBSHVNFOUGPSUZQFDMBTTDPOTUSBJOU
    CZVTJOH“given”LFZXPSE
    ΠϯελϯεએݴͷΠϯϙʔτʹ͸JNQPSUJNQMJFEΛར༻
    HJWFOʹΑΓܕΫϥε੍໿ͷ࣮Ҿ਺Λ໌ࣔతʹ༩͑ΒΕΔ
    import delegate Comparators._
    sort(List(1, 3, 2))
    sort(List(“a”, “c”, “b”)) given stringComparator

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  44. ܕΫϥεΠϯελϯεͷͨΊͷ֦ுϝιου
    &YUFOTJPONFUIPETGPSUZQFDMBTTJOTUBODFT
    w 4DBMBTVQQPSUTOFXTZOUBYGPSEFDMBSJOHFYUFOTJPONFUIPET
    w /FXTZOUBYUBLFTBQBSBNFUFSCFGPSFNFUIPEOBNFBOEUIF
    NFUIPEJTUSFBUFEBTJOTUBODFNFUIPEPGUIFQBSBNFUFSUZQF
    4DBMBͰ͸ΑΓ௚઀తʹ֦ுϝιουΛαϙʔτ͍ͯ͠Δ
    trait Comparator[T] {
    def compare(a: T, b: T): Int
    def (a: T) > (b: T): Boolean = compare(a, b) > 0
    def (a: T) < (b: T): Boolean = compare(a, b) < 0
    }

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  45. ܕΫϥεΠϯελϯεͷͨΊͷ֦ுϝιου
    &YUFOTJPONFUIPETGPSUZQFDMBTTJOTUBODFT
    w compareDBOBMTPCFFYUFOTJPONFUIPE
    w *OUIJTDBTF compareTIPVMECFJNQMFNFOUFEJOJOTUBODF
    EFDMBSBUJPO
    ܕΫϥε͕ཁٻ͢Δϝιου͕֦ுϝιουͰ΋ྑ͍
    trait Comparator[T] {
    def (a: T) compare (b: T): Int
    def (a: T) > (b: T): Boolean = a.compare(b) > 0
    }
    object Comparators {
    delegate for Comparator[Int] {
    def (a: Int) compare (b: Int): Int = a - b
    }
    }

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  46. ܕΫϥε੍໿Λ࣋ͭΠϯελϯεએݴ
    *OTUBODFEFDMBSBUJPOXJUIUZQFDMBTTDPOTUSBJOU
    w “delegate for”EFDMBSBUJPODBOUBLF“given”DMBVTF
    w QBSBNFUFSOBNFJO“given”DMBVTFJTPQUJPOBM
    4DBMBͱҟͳΓɺΠϯελϯεએݴ͸ৗʹEFMFHBUFGPS
    object Comparators {
    delegate TupleComparator [T1, T2] for Comparator[(T1, T2)]
    given Comparator[T1], Comparator[T2]
    {
    def (a: (T1, T2)) compare (b: (T1, T2)): Int = {
    val res1 = a._1.compare(b._1)
    if (res1 == 0) a._2.compare(b._2)
    else res1
    }
    }
    }

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  47. ·ͱΊ
    $PODMVTJPO
    4DBMBͱ4DBMB͸ܕΫϥεͷॻ͖ํ͕େ͖͘ҧ͏
    4DBMBͷํ͕Θ͔Γ΍͍͢
    typeclass
    declaration
    instance
    declaration
    typeclass
    constraint
    extension
    methods
    import
    instance
    declaration
    Scala2 trait
    implicit
    object/val/def
    implicit
    parameter
    implicit 

    class/def
    import
    Scala3 trait delegate for given
    extension
    methods
    import
    delegate

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