Scalaの線形化と抽象型メンバーの統一のジレンマ

セプテーニ・オリジナル 下村 朋之(@s10myk47)
@市ヶ谷Geek★Night#12 ScalaMatsuriの余韻トーク〜祭りの余熱〜


Transcript

1. ScalaͷઢܗԽͱந৅ܕϝϯόʔ ͷ౷ҰͷδϨϯϚ ࢢϲ୩Geek˒Night#12 ScalaMatsuriͷ༨ӆτʔΫʙࡇΓͷ༨೤ʙ
 ηϓςʔχɾΦϦδφϧ Լଜ ๎೭(@s10myk47)
2. ABOUT ME name Լଜ ๎೭(Shimomura Tomoyuki) twitter @s10myk47 organization גࣜձࣾηϓςʔχɾΦϦδφϧ team ਓࣄʹ͓͚Δ࠾༻΍഑ଐΛ࠷దԽ͢ΔαʔϏε DDD, Scala, ࠾༻, μʔπ, αοΧʔ
3. ந৅ܕϝϯόʔ trait A { ɹtype B } ఆٛΛͤͣʹtypeΩʔϫʔυʹΑͬͯந৅ܕΛϝϯόʔͱͯ͠ એݴ͢Δ͜ͱ͕Ͱ͖Δ
4. ্ݶڥք type B <: T Any …. T ….
5. ࣗ෼ܕΞϊςʔγϣϯ trait A {
 self:B => } τϨΠτ͕۩৅Ϋϥεʹؔ͢ΔཁٻΛࢦఆͯ͠ɺBΛલఏͱ͢ ΔΑ͏ʹࢦఆͰ͖Δ
6. SAMPLE CODE trait A {
 type B <: Any
 val b:B
 }
 
 trait ListA {
 self:A =>
 type B <: List[_]
 b.size
 }
7. MOTIVATION
8. SAMPLE CODE trait A {
 type B <: Any
 val b:B
 }
 
 trait ListA {
 self:A =>
 type B <: List[_]
 b.size
 } ListAͷ ந৅ܕϝϯόʔB͸ɺListܕΛ্ݶڥքͱ͢ΔͷͰ bͷ αΠζΛऔಘͰ͖Δͱ͜Λظ଴͢Δ
9. Oops! scala> trait ListA { | self:A => | type B <: List[_] | b.size | } <console>:16: error: value size is not a member of ListA.this.B b.size ^
10. Why..? scalac͸ઢܗԽͷϓϩηεʹ͓͍ͯɺ ෳ਺ͷtraitʹఆٛ͞Ε͍ͯΔந৅ܕϝϯόʔΛ·ͱΊ ͯɺશͯͷ੍໿Λຬͨ͢ந৅ܕϝϯόʔʹ౷Ұ͢Δ͜ ͱ͕Ͱ͖ͳ͍
11. Why..? ୅ΘΓʹ… ந৅ܕϝϯόʔ͸ઢܗԽͷϓϩηεʹ͓͍ͯ࠷ޙͷ΋ ͷ͕࠾༻͞ΕɺͦΕ͕શͯͷ੍໿Λຬ͔ͨ͢Ͳ͏͔Λ ޙͰνΣοΫ͢Δͱ͍͏ํ๏
12. SAMPLE CODE trait A {
 type B <: Any
 val b:B
 }
 
 trait ListA {
 self:A =>
 type B <: List[_]
 b.size
 }
13. Why..? ઢܗԽͷࡍʹந৅ܕϝϯόʔBΛ·ͱΊͯ 
 ͱͯ͠΄͍͕͠ɺɺɺ type B <: List[_] <: Any
14. Why..? ࠷ޙʹདྷͨ B ͕࠾༻͞ΕΔ
 ListAͷޙʹA͕དྷΔͷͰɺ ந৅ܕϝϯόʔ B ͸ AͷB ͕࠾༻͞ΕΔ trait ListA {
 self:Aɹ=>
 type B <: List[_]
 b.size
 }
15. Why..? trait A {
 type B <: Any
 val b:B
 }
 
 trait ListA {
 self:A =>
 type B <: List[_]
 b.size
 } trait AͷB͸ AnyΛܧঝ͢Δͱ͍͏੍໿͔࣋ͬͯ͠ͳ͍ Anyʹsizeؔ਺ͳ͍ͷͰ…
16. Oops! scala> trait ListA { | self:A => | type B <: List[_] | b.size | } <console>:16: error: value size is not a member of ListA.this.B b.size ^
17. What should I do ? trait ListA {
 self:A with ListA =>
 type B <: List[_]
 b.size
 } ࣗ෼ܕΞϊςʔγϣϯͰઢܗԽͷॱ൪Λ ListA ͕ޙʹདྷΔΑ ͏ʹ໌ࣔ͢Δ
18. DOT FIXES THIS! Martin Odersky added a comment - 15/Mar/13 8:30 AM 
 Paul, you are correct on all counts. This is indeed a fundamental problem in Scala's type system (also in its theory, \nu-Obj): Abstract type members are linearized and the last one wins. It is later checked that that last one has a constraint that implies all others. But there is never a unification of constraints. DOT fixes this.
19. TRY ؀ڥߏஙʹ͍ͭͯ͸ͪ͜Β http://dotty.epfl.ch/#getting-started
20. SUMMARY ɾscalac͸ઢܗԽͷϓϩηεʹ͓͍ͯɺ ෳ਺ͷtraitʹఆٛ͞Ε͍ͯΔந৅ܕϝϯόʔΛ·ͱΊ ͯɺશͯͷ੍໿Λຬͨ͢ந৅ܕϝϯόʔʹ౷Ұ͢Δ͜ ͱ͕Ͱ͖ͳ͍ ɾࣗ෼ܕΞϊςʔγϣϯͰઢܗԽͷॱ൪Λ ListA ͕ޙʹདྷΔ Α͏ʹ໌ࣔͯ͠ճආ ɾDottyͰ͸fixͨ͠Α
21. ηϓςʔχΦϦδφϧੵۃ࠾༻தʂ DDD Scala TDD Angular2 Swift3 Android εΫϥϜ ࡋྔ࿑ಇ