Generalized existentialが内部的にすでに存在しているか調べてみた / A Dive to Find Inner Generalized Existential Containers

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Generalized existen.al͕಺෦తʹ͢ Ͱʹଘࡏ͍ͯ͠Δ͔ௐ΂ͯΈͨ Yuta Koshizawa @koher

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① ٙ໰ʹࢥͬͨ͜ͱ

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͜ͷίʔυͷ S ͕ಛघԽ͞Εͳ͍৔߹ɺ sequence ͷ࣮ߦ࣌ͷ಺෦తදݱ͸Ͳ͏ͳͬͯΔʁ func sum(of sequence: S) -> Int where S.Element == Int { return sequence.reduce(0, +) }

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΋ͬͱஸೡʹ

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associatedtype Λ࣋ͨͳ͍ϓϩτίϧ protocol Animal {} struct Cat: Animal {} let cat: Cat = Cat() let animal: Animal = cat // OK

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ϓϩτίϧܕม਺ͷαΠζ protocol Animal {} struct Cat: Animal { let a: Int8 } struct Dog: Animal { let b: Int32 } let cat: Cat = Cat(a: 2) // 1 όΠτ let dog: Dog = Dog(b: 3) // 4 όΠτ // ԿόΠτʁ ! let animal: Animal = Bool.random() ? cat : dog

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஋ܕͱϓϩτίϧܕͱσΟεύον protocol Animal { func foo() -> Int } struct Cat: Animal { func foo() -> Int { return 2 } } struct Dog: Animal { func foo() -> Int { return 3 } } let cat: Cat = Cat() let dog: Dog = Dog() _ = cat.foo() // 2 : ੩తσΟεύον _ = dog.foo() // 3 : ੩తσΟεύον

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஋ܕͱϓϩτίϧܕͱσΟεύον protocol Animal { func foo() -> Int } struct Cat: Animal { func foo() -> Int { return 2 } } struct Dog: Animal { func foo() -> Int { return 3 } } let cat: Cat = Cat() let dog: Dog = Dog() let animal: Animal = Bool.random() ? cat : dog _ = animal.foo() // 2 or 3 : ಈతσΟεύον

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Existen(al containers 1 struct OpaqueExistentialContainer { void *fixedSizeBuffer[3]; Metadata *type; WitnessTable *witnessTables[NUM_WITNESS_TABLES]; }; 1 h$ps:/ /github.com/apple/swi6/blob/master/docs/ABI/TypeLayout.rst#existenBal-container-layout

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ෳ਺ͷ Witness table Λ࣋ͭ৔߹ protocol P {} protocol Q {} struct S : P, Q {} let pq: P & Q = S()

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! Existen(al container ͷ͓͔͛Ͱ ந৅తͳϓϩτίϧܕͱͯ͠ѻ͑Δ

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associatedtype Λ࣋ͭϓϩτίϧ protocol Animal { associatedtype Value } struct Cat: Animal { typealias Value = Int } let cat: Cat = Cat() let animal: Animal = cat // NG

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Generalized existen.als 2 let strings : Any = ["a", "b", "c"] 2 h$ps:/ /github.com/apple/swi6/blob/master/docs/GenericsManifesto.md#generalized-existenAals

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associatedtype Λ࣋ͭϓϩτίϧ protocol Animal { associatedtype Value } struct Cat: Animal { typealias Value = Int } let cat: Cat = Cat() let animal: Any = cat // Generalized existential Ͱ͜Ε͕Ͱ͖ΔΑ͏ʹͳΔ͔΋

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! Generalized existen.al ͕ͳ͍ͷͰ associatedype ͕͋Δͱ ϓϩίτϧܕͱͯ͠ѻ͑ͳ͍

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Ͱ΋ɺ͜Ε͸Ͱ͖Δ protocol Animal { associatedtype Value } struct Cat: Animal { typealias Value = Int } func useAnimal(_ animal: A) -> Int where A.Value == Int { ... } useAnimal(Cat()) // ✅ OK

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A ͕ Cat ʹಛघԽ͞ΕΔͱ͜͏ͳΔ protocol Animal { associatedtype Value } struct Cat: Animal { typealias Value = Int } func useAnimal(_ animal: Cat) -> Int { ... } useAnimal(Cat()) // ✅ OK

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ಛघԽ͞Εͳ͍ͱͲ͏ͳΔʁ protocol Animal { associatedtype Value } struct Cat: Animal { typealias Value = Int } func useAnimal(_ animal: A) -> Int where A.Value == Int { ... } useAnimal(Cat()) // `Cat` ͸ͲͷΑ͏ʹѻΘΕΔʁ

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! ΋͔ͯ͠͠಺෦తʹ͸ Existen(al ʹͳ͍ͬͯΔͷͰ͸ʁ

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② LLVM IR Ͱ಺෦తදݱΛௐࠪ

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associatedtype ͕ ͳ͍ ͱ͖

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associatedtype ͕ ͳ͍ ͱ͖ protocol Animal { func foo() -> Int } struct Cat: Animal { var value: Int = 42 func foo() -> Int { return value } }

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associatedtype ͕ ͳ͍ ͱ͖ func useAnimal(_ animal: Animal) -> Int { return animal.foo() } func useCat(_ cat: Cat) -> Int { return useAnimal(cat) } print(useCat(Cat()))

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associatedtype ͕ ͳ͍ ͱ͖ func useAnimal(_ animal: Animal) -> Int { return animal.foo() } func useCat(_ cat: Cat) -> Int { return useAnimal(cat) } print(useCat(Cat()))

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swiftc -emit-ir foo.swift

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associatedtype ͕ ͳ͍ ͱ͖ define hidden swiftcc i64 @"$S4main9useAnimalySiAA0C0_pF"(%T4main6AnimalP* noalias nocapture dereferenceable(40)) #0 { entry: %1 = getelementptr inbounds %T4main6AnimalP, %T4main6AnimalP* %0, i32 0, i32 1 %2 = load %swift.type*, %swift.type** %1, align 8 %3 = getelementptr inbounds %T4main6AnimalP, %T4main6AnimalP* %0, i32 0, i32 2 %4 = load i8**, i8*** %3, align 8 %5 = getelementptr inbounds %T4main6AnimalP, %T4main6AnimalP* %0, i32 0, i32 0 %6 = call %swift.opaque* @__swift_project_boxed_opaque_existential_1([24 x i8]* %5, %swift.type* %2) #1 %7 = getelementptr inbounds i8*, i8** %4, i32 1 %8 = load i8*, i8** %7, align 8, !invariant.load !25 %9 = bitcast i8* %8 to i64 (%swift.opaque*, %swift.type*, i8**)* %10 = call swiftcc i64 %9(%swift.opaque* noalias nocapture swiftself %6, %swift.type* %2, i8** %4) ret i64 %10 }

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swift demangle S4main9useAnimalySiAA0C0_pF

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σϚϯάϦϯάͷ݁Ռ $ swift demangle S4main9useAnimalySiAA0C0_pF $S4main9useAnimalySiAA0C0_pF ---> main.useAnimal(main.Animal) -> Swift.Int

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associatedtype ͕ ͳ͍ ͱ͖ %T4main6AnimalP = type { [24 x i8], %swift.type*, i8** }

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associatedtype ͕ ͳ͍ ͱ͖ %T4main6AnimalP = type { [24 x i8], %swift.type*, i8** } ↕ ରԠ͍ͯ͠Δ struct OpaqueExistentialContainer { void *fixedSizeBuffer[3]; Metadata *type; WitnessTable *witnessTables[NUM_WITNESS_TABLES]; };

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Witness tables ͱϙΠϯλܕ • i8* : witness table ͷཁૉ • i8** : witness table • i8*** : witness table ͷू·Γ = witnessTables

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ෳ਺ͷ Witness table Λ࣋ͭ৔߹ protocol P {} protocol Q {} struct S : P, Q {} let pq: P & Q = S() ↓ LLVM IR ( P & Q ) %T4main1P_AA1Qp = type { [24 x i8], %swift.type*, i8**, i8** }

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associatedtype ͕ ͳ͍ ͱ͖ %T4main6AnimalP = type { [24 x i8], %swift.type*, i8** } ↕ ରԠ͍ͯ͠Δ struct OpaqueExistentialContainer { // 40 όΠτ void *fixedSizeBuffer[3]; // 24 όΠτ Metadata *type; // 8 όΠτ WitnessTable *witnessTable; // 8 όΠτ };

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Existen(al container ͷαΠζ protocol P {} protocol Q {} print(MemoryLayout

.size) // 40 print(MemoryLayout

.size) // 48

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getelementptr 3 = getelementptr , * {, [inrange] }* = getelementptr inbounds , * {, [inrange] }* 3 h$p:/ /llvm.org/docs/LangRef.html#getelementptr-instruc=on

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associatedtype ͕ ͳ͍ ͱ͖ define hidden swiftcc i64 @"$S4main9useAnimalySiAA0C0_pF"(%T4main6AnimalP* noalias nocapture dereferenceable(40)) #0 { entry: %1 = getelementptr inbounds %T4main6AnimalP, %T4main6AnimalP* %0, i32 0, i32 1 // getelementptr inbounds , * , , %2 = load %swift.type*, %swift.type** %1, align 8 %3 = getelementptr inbounds %T4main6AnimalP, %T4main6AnimalP* %0, i32 0, i32 2 %4 = load i8**, i8*** %3, align 8 %5 = getelementptr inbounds %T4main6AnimalP, %T4main6AnimalP* %0, i32 0, i32 0 %6 = call %swift.opaque* @__swift_project_boxed_opaque_existential_1([24 x i8]* %5, %swift.type* %2) #1 %7 = getelementptr inbounds i8*, i8** %4, i32 1 %8 = load i8*, i8** %7, align 8, !invariant.load !25 %9 = bitcast i8* %8 to i64 (%swift.opaque*, %swift.type*, i8**)* %10 = call swiftcc i64 %9(%swift.opaque* noalias nocapture swiftself %6, %swift.type* %2, i8** %4) ret i64 %10 } 0 ൪໨ͷ %T4main6AnimalP ͷ 1 ൪໨ͷϝϯόͷϙΠϯλΛऔಘ

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associatedtype ͕ ͋Δ ͱ͖

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associatedtype ͕ ͋Δ ͱ͖ protocol Animal { associatedtype Value func foo() -> Value } struct Cat: Animal { var value: Int = 42 func foo() -> Int { return value } }

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associatedtype ͕ ͋Δ ͱ͖ func useAnimal(_ animal: A) -> Int where A.Value == Int { return animal.foo() } func useCat(_ cat: Cat) -> Int { return useAnimal(cat) } print(useCat(Cat()))

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associatedtype ͕ ͋Δ ͱ͖ define hidden swiftcc i64 @"$S4main9useAnimalySixAA0C0RzSi5ValueRtzlF"(%swift.opaque* noalias nocapture, %swift.type* %A, i8** %A.Animal) #0 { entry: %1 = alloca %TSi, align 8 %2 = bitcast %TSi* %1 to i8* call void @llvm.lifetime.start.p0i8(i64 8, i8* %2) %3 = getelementptr inbounds i8*, i8** %A.Animal, i32 2 %4 = load i8*, i8** %3, align 8, !invariant.load !28 %5 = bitcast i8* %4 to void (%swift.opaque*, %swift.opaque*, %swift.type*, i8**)* %6 = bitcast %TSi* %1 to %swift.opaque* call swiftcc void %5(%swift.opaque* noalias nocapture sret %6, %swift.opaque* noalias nocapture swiftself %0, %swift.type* %A, i8** %A.Animal) %._value = getelementptr inbounds %TSi, %TSi* %1, i32 0, i32 0 %7 = load i64, i64* %._value, align 8 %8 = bitcast %TSi* %1 to i8* call void @llvm.lifetime.end.p0i8(i64 8, i8* %8) ret i64 %7 }

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associatedtype ͕ ͋Δ ͱ͖ protocol Animal { associatedtype Value func foo() -> Value } struct Cat: Animal { var value: Int = 42 func foo() -> Int { return value } }

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associatedtype ͕ ͋Δ ͱ͖ func useAnimal(_ animal: A) -> Int where A.Value == Int { return animal.foo() } func useCat(_ cat: Cat) -> Int { return useAnimal(cat) } print(useCat(Cat()))

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associatedtype ͕ ͋Δ ͱ͖ define hidden swiftcc i64 @"$S4main6useCatySiAA0C0VF"(i64) #0 { entry: %1 = alloca %T4main3CatV, align 8 %2 = bitcast %T4main3CatV* %1 to i8* call void @llvm.lifetime.start.p0i8(i64 8, i8* %2) %.value = getelementptr inbounds %T4main3CatV, %T4main3CatV* %1, i32 0, i32 0 %.value._value = getelementptr inbounds %TSi, %TSi* %.value, i32 0, i32 0 store i64 %0, i64* %.value._value, align 8 %3 = bitcast %T4main3CatV* %1 to %swift.opaque* %4 = call swiftcc i64 @"$S4main9useAnimalySixAA0C0RzSi5ValueRtzlF"( %swift.opaque* noalias nocapture %3, %swift.type* bitcast ( i64* getelementptr inbounds ( <{ i8**, i64, <{ i32, i32, i32, i32, i32, i32 }>*, i32, [4 x i8] }>, <{ i8**, i64, <{ i32, i32, i32, i32, i32, i32 }>*, i32, [4 x i8] }>* @"$S4main3CatVMf", i32 0, i32 1 ) to %swift.type* ), i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @"$S4main3CatVAA6AnimalAAWP", i32 0, i32 0) ) %5 = bitcast %T4main3CatV* %1 to i8* call void @llvm.lifetime.end.p0i8(i64 8, i8* %5) ret i64 %4 } useCat ͷ LLVM IR

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S4main3CatVAA6AnimalAAWP ΛσϚϯάϦϯά $ swift demangle S4main3CatVAA6AnimalAAWP $S4main3CatVAA6AnimalAAWP ---> protocol witness table for main.Cat : main.Animal in main

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S4main3CatVAA6AnimalAAWP ΛσϚϯάϦϯά $ swift demangle S4main3CatVAA6AnimalAAWP $S4main3CatVAA6AnimalAAWP ---> protocol witness table for main.Cat : main.Animal in main ^^^^^^^^^^^^^^^^^^^^^^^^^^

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! Existen(al container Ͱ ౉͞ͳ͍ͷ͸ͳͥʁ

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associatedtype ͕ ͋Δ ͱ͖ func useAnimal(_ animal: A) -> Int where A.Value == Int { return animal.foo() } func useCat(_ cat: Cat) -> Int { return useAnimal(cat) } print(useCat(Cat()))

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A ܕ͸ useCat ͷத͚ͩͷܕ

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! useCat ͷϩʔΧϧείʔϓͰ औΓѻ͑Ε͹ྑ͍

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! Existen(al container Ͱ औΓճ͢ඞཁ͸ͳ͍

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! Existen(al container Ͱ แΜͩΓ෼ղͨ͠Γ͢Δͱ Φʔόʔϔου͕ൃੜ

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! ͦΕͳΒ Existen)al ʹͤͣ ࠷ॳ͔Β͹Β͹Βʹѻ͓͏ ʢͱ͍͏͜ͱͰ͸ʁʣ

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ʲ౰ॳͷٙ໰ʳ ΋͔ͯ͠͠಺෦తʹ͸ Existen(al ʹͳ͍ͬͯΔͷͰ͸ʁ

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! Generalized existen.al ͸ ಺෦తʹ΋ଘࡏ͠ͳ͔ͬͨ

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! Ͱ΋ useCat(_:) ͸ Existen(al ͱࣅͨ࢓૊ΈͰಈ͍ͯͨ

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No content

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΄΅ಉ͜͡ͱ͕͔֬ΊΒΕͯͨ 4 4 h$ps:/ /qiita.com/omochimetaru/items/b41e7699ea25a324aefa

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͓͠·͍