https://www.youtube.com/watch?v=lOY0YkH_5cA https://fortee.jp/iosdc-japan-2018/proposal/1056b7c9-d1ab-4c66-b6a7-e37254b969ee
ίϯύΠϥ͔Βඥղ͘4XJGUNFUIPEEJTQBUDI!LBUFJOPJHBLVLVO
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ࣗݾհw !LBUFJOPJHBLVLVOw ૣҴాେֶߴֶӃ̏
͍͖ͳΓͰ͕͢
ΫΠζͰ͢
class Cat {func bark() -> String {return "ʹΌΜ"}}class Dog {func bark() -> String {return "ΘΜ"}}let cat = Cat()let dog = unsafeBitCast(cat, to: Dog.self)print(dog.bark())2Կ͕ग़ྗ͞ΕΔͰ͠ΐ͏ʁʹΌΜPSΘΜ
class Cat {func bark() -> String {return "ʹΌΜ"}}class Dog {func bark() -> String {return "ΘΜ"}}let cat = Cat()let dog = unsafeBitCast(cat, to: Dog.self)print(dog.bark())2Կ͕ग़ྗ͞ΕΔͰ͠ΐ͏ʁ"ΘΜ
ʮΘΜʯ
ࠓ͢͜ͱw .FUIPE%JTQBUDIͷΈw ࠷దԽͷΈw ύϑΥʔϚϯε
2.FUIPEEJTQBUDIͱʁ
2.FUIPEEJTQBUDIͱʁ"ϝιου͕ݺͼग़͞ΕΔ࣌ʹɺ ࣮ࡍʹͲͷϝιουΛ࣮ߦ͢Δ͔ΛܾΊΔػߏ
class Animal {func bark() {print("ΞχϚϧͰ͢")}}class Cat: Animal {override func bark() {print("ʹΌΜ")}}func callAnimalBark(_ animal: Animal) {animal.bark()}
class Animal {func bark() {print("ΞχϚϧͰ͢")}}class Cat: Animal {override func bark() {print("ʹΌΜ")}}func callAnimalBark(_ animal: Animal) {animal.bark() // ΞχϚϧͰ͢ or ʹΌΜ}
class Animal {func bark() {print("ΞχϚϧͰ͢")}}class Cat: Animal {override func bark() {print("ʹΌΜ")}}func callAnimalBark(_ animal: Animal) {animal.bark() // ΞχϚϧͰ͢ or ʹΌΜ}࣮ߦ͞ΕΔϝιουͲͬͪʁʁ
.FUIPE%JTQBUDIͷύλʔϯw 4UBUJD%JTQBUDIw ݺͼग़͢ϝιουΛίϯύΠϧ࣌ʹܾΊΔw %ZOBNJD%JTQBUDIw ݺͼग़͢ϝιουΛ࣮ߦ࣌ʹܾΊΔ
4UBUJD%JTQBUDIw ؔw ܕͷϝιουw FYUFOTJPOʹॻ͍ͨϝιουw pOBMͳϝιουstruct S {func foo() {}}let s = S()s.foo()
4UBUJD%JTQBUDIstruct S {func foo() {}}let s = S()s.foo()ಉ͡γάωνϟͷϝιου͕ଘࡏ͠ͳ͍w ؔw ܕͷϝιουw FYUFOTJPOʹॻ͍ͨϝιουw pOBMͳϝιου
%ZOBNJD%JTQBUDIw $MBTTͷϝιουw 1SPUPDPMͷϝιουprotocol Animal {func foo()}struct Cat: Animal {func foo() {}}func callFoo(_ animal: T) {animal.foo()}
w $MBTTͷϝιουΦʔόʔϥΠυw 1SPUPDPMͷϝιουෳͷܕ͕४ڌ%ZOBNJD%JTQBUDIprotocol Animal {func foo()}struct Cat: Animal {func foo() {}}func callFoo(_ animal: T) {animal.foo()}ಉ͡γάωνϟͷϝιου͕ෳଘࡏ͢Δ
.FUIPE%JTQBUDIͷύλʔϯw 4UBUJD%JTQBUDIw ݺͼग़͢ϝιουΛίϯύΠϧ࣌ʹܾΊΔw %ZOBNJD%JTQBUDIw ݺͼग़͢ϝιουΛ࣮ߦ࣌ʹܾΊΔw 75BCMFw 8JUOFTT5BCMF
75BCMFw Ծؔςʔϒϧ͔ΒϝιουΛ୳ࡧ͢Δ%JTQBUDIํࣜw ΫϥεͷϝιουΛݺͼग़࣌͢ʹ͏w ΠϯελϯεͷϝλσʔλʹຒΊࠐ·ΕΔ
func Animal.bark()*Animal.bark75BCMFGPS"OJNBMclass Animal {func bark() {}}
func Animal.bark()*Animal.bark75BCMFGPS$BU*Animal.bark75BCMFGPS"OJNBMclass Animal {func bark() {}}class Cat: Animal {}
func Cat.foo()func Animal.bark()*Animal.bark*Animal.bark*Cat.foo75BCMFGPS"OJNBM75BCMFGPS$BUclass Animal {func bark() {}}class Cat: Animal {func foo() {}}
class Animal {func bark() {}}class Cat: Animal {override func bark() {}func foo() {}}75BCMFGPS$BUfunc Animal.bark()75BCMFGPS"OJNBM*Animal.bark*Animal.bark*Cat.foofunc Cat.bark()func Cat.foo()
8JUOFTT5BCMFw Ծؔςʔϒϧ͔ΒϝιουΛ୳ࡧ͢Δ%JTQBUDIํࣜw ϓϩτίϧͷϝιουΛݺͼग़࣌͢ʹ͏w ϓϩτίϧͷ४ڌ͝ͱʹఆٛ͞ΕΔ
protocol Animal {func bark()}
protocol Animal {func bark()}struct Dog: Animal {func bark() {}}8JUOFTT5BCMFGPS"OJNBMJODPOGPSNBODF%PH*Animal.barkfunc Animal.bark(dog) {Dog.bark(dog)}8JUOFTTNFUIPEGPS"OJNBMJODPOGPSNBODF%PH
ʮΘΜʯ
class Cat {func bark() -> String {return "ʹΌΜ"}}class Dog {func bark() -> String {return “ΘΜ"}}let cat = Cat()let dog = unsafeBitCast(cat, to: Dog.self)print(dog.bark())ϝϞϦϨΠΞτมߋ͞Εͳ͍ࢀর͢ΔVTableมΘΒͳ͍Catͷςʔϒϧ͕ࢀর͞ΕΔʮʹΌΜʯ͕ग़ྗ͞ΕΔͣʂ
͔͠͠ɺ
class Cat {func bark() -> String {return "ʹΌΜ"}}class Dog {func bark() -> String {return "ΘΜ"}}let cat = Cat()let dog = unsafeBitCast(cat, to: Dog.self)print(dog.bark()) // ΘΜʮΘΜʯ
࠷దԽΛΦϑʹͯ͠ΈΔ
$ swiftc -frontend -c -primary-file animal.swift$ swiftc animal.o$ ./animalʹΌΜʮʹΌΜʯ
࠷దԽͷաఔʹԿ͔͋Γͦ͏
%FWJSUVBMJ[F
%FWJSUVBMJ[Fw 4*-0QUJNJ[FSͷ࠷దԽύεw %ZOBNJD%JTQBUDIΛ4UBUJD%JTQBUDIʹ࠷దԽ͢Δw ίϯύΠϧ࣌ͷܕใ͔ΒϝιουΛ̍ͭʹܾΊΔ
75BCMFͷ࠷దԽ
USZ%FWJSUVBMJ[F"QQMZauto &M = FAS.getModule();auto Instance = stripUpCasts(CMI->getOperand());auto ClassType = Instance->getType();...if (isEffectivelyFinalMethod(FAS, ClassType, CD, CHA))return tryDevirtualizeClassMethod(FAS, Instance, ORE,true /*isEffectivelyFinalMethod*/);if (auto Instance = getInstanceWithExactDynamicType(CMI->getOperand(),CMI->getModule(),CHA))return tryDevirtualizeClassMethod(FAS, Instance, ORE);if (auto ExactTy = getExactDynamicType(CMI->getOperand(), CMI->getModule(),CHA)) {if (ExactTy == CMI->getOperand()->getType())return tryDevirtualizeClassMethod(FAS, CMI->getOperand(), ORE);}MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
USZ%FWJSUVBMJ[F"QQMZauto &M = FAS.getModule();auto Instance = stripUpCasts(CMI->getOperand());auto ClassType = Instance->getType();...if (isEffectivelyFinalMethod(FAS, ClassType, CD, CHA))return tryDevirtualizeClassMethod(FAS, Instance, ORE,true /*isEffectivelyFinalMethod*/);if (auto Instance = getInstanceWithExactDynamicType(CMI->getOperand(),CMI->getModule(),CHA))return tryDevirtualizeClassMethod(FAS, Instance, ORE);if (auto ExactTy = getExactDynamicType(CMI->getOperand(), CMI->getModule(),CHA)) {if (ExactTy == CMI->getOperand()->getType())return tryDevirtualizeClassMethod(FAS, CMI->getOperand(), ORE);}Πϯελϯεͷ࣮ߦ࣌ͷܕ͕੩తʹܾఆͰ͖ΔύλʔϯMJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
%FWJSUVBMJ[FGPS75BCMFclass Animal {func bark() {}}class Cat: Animal {override func bark() {}}let animal: Animal = Cat() // ΠχγϟϥΠβ͔Β࡞ͬͯΔͷͰCatܕanimal.bark()Πϯελϯεͷ࣮ߦ࣌ͷܕ͕੩తʹܾఆͰ͖Δύλʔϯ
USZ%FWJSUVBMJ[F"QQMZauto &M = FAS.getModule();auto Instance = stripUpCasts(CMI->getOperand());auto ClassType = Instance->getType();...if (isEffectivelyFinalMethod(FAS, ClassType, CD, CHA))return tryDevirtualizeClassMethod(FAS, Instance, ORE,true /*isEffectivelyFinalMethod*/);if (auto Instance = getInstanceWithExactDynamicType(CMI->getOperand(),CMI->getModule(),CHA))return tryDevirtualizeClassMethod(FAS, Instance, ORE);if (auto ExactTy = getExactDynamicType(CMI->getOperand(), CMI->getModule(),CHA)) {if (ExactTy == CMI->getOperand()->getType())return tryDevirtualizeClassMethod(FAS, CMI->getOperand(), ORE);}ϝιου͕z࣮࣭pOBMzͳύλʔϯMJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
JT&⒎FDUJWFMZ'JOBM.FUIPEstatic bool isEffectivelyFinalMethod(FullApplySite AI,SILType ClassType,ClassDecl *CD,ClassHierarchyAnalysis *CHA) {if (CD && CD->isFinal())return true;const DeclContext *DC = AI.getModule().getAssociatedContext();auto *CMI = cast(AI.getCallee());if (!calleesAreStaticallyKnowable(AI.getModule(), CMI->getMember()))return false;auto *Method = CMI->getMember().getAbstractFunctionDecl();if (!Method->isOverridden())return true;...return true;}ϝιου͕z࣮࣭pOBMzͳύλʔϯMJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
DBMMFFT"SF4UBUJDBMMZ,OPXBCMFbool swift::calleesAreStaticallyKnowable(SILModule &M, SILDeclRef Decl) {...switch (AFD->getEffectiveAccess()) {case AccessLevel::Open:return false;case AccessLevel::Public:if (isa(AFD)) {auto *ND = AFD->getDeclContext()->getSelfNominalTypeDecl();if (ND->getEffectiveAccess() == AccessLevel::Open)return false;}case AccessLevel::Internal:return M.isWholeModule();case AccessLevel::FilePrivate:case AccessLevel::Private:return true;}}ϝιουΛ੩తʹܾఆͰ͖ΔύλʔϯMJC4*-0QUJNJ[FS6UJMT-PDBMDQQ
JT&⒎FDUJWFMZ'JOBM.FUIPEstatic bool isEffectivelyFinalMethod(FullApplySite AI,SILType ClassType,ClassDecl *CD,ClassHierarchyAnalysis *CHA) {...if (!Method->isOverridden())return true;ClassHierarchyAnalysis::ClassList Subs;getAllSubclasses(CHA, CD, ClassType, AI.getModule(), Subs);auto *ImplMethod = CD->findImplementingMethod(Method);for (auto S : Subs) {auto *ImplFD = S->findImplementingMethod(Method);if (ImplFD != ImplMethod)return false;}return true;}ϝιου͕z࣮࣭pOBMzͳύλʔϯMJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
0WFSSJEF͞ΕͭͭΠϯελϯε͕ͦͷαϒΫϥεʹͳΓಘͳ͍߹class Cat {func bark() {}}enum Tama {}enum Kuro {}class TamaCat: Cat {override func bark() {}}func callBark(cat: Cat) {cat.bark()}
class Cat {func bark() {}}enum Tama {}enum Kuro {}// CatͷαϒλΠϓͰͳ͍class TamaCat: Cat {override func bark() {}}func callBark(cat: Cat) {cat.bark()}0WFSSJEF͞ΕͭͭΠϯελϯε͕ͦͷαϒΫϥεʹͳΓಘͳ͍߹
JT&⒎FDUJWFMZ'JOBM.FUIPEϝιου͕z࣮࣭pOBMzͳύλʔϯ
class Cat {func bark() -> String {return “ʹΌΜ"}}class Dog {func bark() -> String {return "ΘΜ"}}let cat = Cat()let dog = unsafeBitCast(cat, to: Dog.self)print(dog.bark()) // ΘΜ࠷దԽ͋Γͷ߹Dog.barkϝιουnon-finalΦʔόʔϥΠυ͞Ε͍ͯͳ͍ͷͰ”࣮࣭final”dog.bark()͕Static Dispatchʹ࠷దԽ͞ΕΔ
࠷దԽͳ͠ͷ߹class Cat {func bark() -> String {return “ʹΌΜ"}}class Dog {func bark() -> String {return "ΘΜ"}}let cat = Cat()let dog = unsafeBitCast(cat, to: Dog.self)print(dog.bark()) // ʹΌΜWhole Module࠷దԽ͕ΦϑϞδϡʔϧͰΦʔόʔϥΠυ͞ΕΔՄೳੑ͕͋ΔΠϯελϯεͷϝλσʔλͷVTable͔ΒDynamic Dispatch͢Δ
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