Tuples conform to Equatable, Comparable, and Hashableの実装

わいわいswiftc #24 https://iosdiscord.connpass.com/event/199431/

Transcript

1. Tuples conform to Equatable,
   Comparable, and Hashableͷ࣮૷
   Θ͍Θ͍swiftc #22
   @kateinoigakukun
   1
   

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2. ࣗݾ঺հ
   @kateinoigakukun
   • Merpay Expert Team Πϯλʔϯ
   • SwiftWasmϝϯςφ
   2
   

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3. ࠓ·Ͱͷ໰୊
   let points = [(x: 128, y: 316), (x: 0, y: 0), (x: 100, y: 42)]
   let origin = (x: 0, y: 0)
   // error: type '(x: Int, y: Int)' cannot conform to 'Equatable';
   // only struct/enum/class types can conform to protocols
   if points.contains(origin) {
   // do some serious calculations here
   }
   // error: type '(x: Int, y: Int)' cannot conform to 'Comparable';
   // only struct/enum/class types can conform to protocols
   let sortedPoints = points.sorted()
   // error: type '(x: Int, y: Int)' cannot conform to 'Hashable';
   // only struct/enum/class types can conform to protocols
   let uniquePoints = Set(points)
   3
   

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4. λϓϧ͕͋Δͱࣗಈ࣮૷΋Ͱ͖ͳ͘ͳͬͯͨ
   struct Restaurant {
   let name: String
   let location: (latitude: Int, longitude: Int)
   }
   // error: type 'Restaurant' does not conform to protocol 'Equatable'
   extension Restaurant: Equatable {}
   // error: type 'Restaurant' does not conform to protocol 'Hashable'
   extension Restaurant: Hashable {}
   4
   

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5. ࣮͸͢ͰʹΦʔόʔϩʔυ͸͋Δ
   SE-0015: Tuple comparison operators
   .gybͰίʔυੜ੒͞ΕͯΔɻ
   @warn_unused_result
   public func == (lhs: (A,B,C), rhs: (A,B,C)) -> Bool {
   return lhs.0 == rhs.0 && lhs.1 == rhs.1 && lhs.2 == rhs.2
   }
   @warn_unused_result
   public func < (lhs: (A,B,C), rhs: (A,B,C)) -> Bool {
   if lhs.0 != rhs.0 { return lhs.0 < rhs.0 }
   if lhs.1 != rhs.1 { return lhs.1 < rhs.1 }
   return lhs.2 < rhs.2
   }
   ...
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6. SE-0283ͱ͸
   શͯͷཁૉ͕EquatableɺComparableɺHashableͷ͍ͣΕ͔ʹ
   ४ڌ͍ͯ͠Δ৔߹ɺλϓϧࣗମ΋ͦͷϓϩτίϧʹ४ڌ͢Δ
   ϓϩϙʔβϧ͸डཧ͞Εɺ࣮૷΋͋Δ͕ϝΠϯετϦʔϜʹ͸
   ೖͬͯͳ͍
   https://github.com/apple/swift-evolution/blob/master/proposals/0283-tuples-are-equatable-comparable-hashable.md 6
   

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7. func isEqual(_ lhs: T, _ rhs: T) -> Bool { lhs == rhs }
   // Ok, Int is Equatable thus the tuples are Equatable
   isEqual((1, 2, 3), (1, 2, 3)) // true
   struct EmptyStruct {}
   // error: type '(EmptyStruct, Int, Int)' does not conform to protocol 'Equatable'
   // note: value of type 'EmptyStruct' does not conform to protocol 'Equatable',
   // preventing conformance of '(EmptyStruct, Int, Int)' to 'Equatable'
   isEqual((EmptyStruct(), 1, 2), (EmptyStruct(), 1, 2))
   // We don't take into account the labels for equality.
   isEqual((x: 0, y: 0), (0, 0)) // true
   7
   

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8. func isLessThan(_ lhs: T, _ rhs: T) -> Bool { lhs < rhs }
   let origin = (x: 0, y: 0)
   let randomPoint = (x: Int.random(in: 1 ... 10), y: Int.random(in: 1 ... 10))
   // In this case, the first element of origin is 0 and the first element
   // of randomPoint is somewhere between 1 and 10, so they are not equal.
   // origin's element is less than randomPoint's, thus true.
   isLessThan(origin, randomPoint) // true
   // We don't take into account the labels for comparison.
   isLessThan((x: 0, y: 0), (1, 0)) // true
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9. let points = [(x: 0, y: 0), (x: 1, y: 2), (x: 0, y: 0)]
   let uniquePoints = Set(points)
   // Create a grid system to hold game entities.
   var grid = [(x: Int, y: Int): Entity]()
   for point in uniquePoints {
   grid[point]?.move(up: 10)
   }
   // We don't take into account the labels for hash value.
   (x: 0, y: 0).hashValue == (0, 0).hashValue // true
   grid[(x: 100, y: 200)] = Entity(name: "Pam")
   print(grid[(100, 200)]) // Entity(name: "Pam")
   9
   

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10. ࣮૷ํ਑
    λϓϧͷϓϩτίϧద߹ΛҰൠԽ͢Δͷ͸ϋʔυͳͷͰɺ
    EquatableɺComparableɺHashableʹରͯ͠ΞυϗοΫͳ࣮૷
    Λ͢ΔɻίϯύΠϥతʹ͸ٕज़ෛ࠴ʹͳΔ͕ɺଟ͘ͷϢʔβʔ
    Λٹ͏͜ͱΛ༏ઌͯ͠Δɻ
    ࢀߟɿSpecial Case Protocol Conformance: Long-term
    Tradeoffs for Near-term Conformance
    10
    

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11. • ຊ౰͸͜͏͍͏ίʔυΛඪ४ϥΠϒϥϦʹೖΕ͓͚ͯͩ͘ʹ
    ͍ͨ͠ɻ
    • ͕ɺҰൠԽ͢Δʹ͸Մม௕δΣωϦΫεͳͲͷॏΊͷݴޠػ
    ೳ͕ඞཁ
    extension Tuple: Equatable where T1: Equatable, T2: Equatable, ... {
    public static func ==(_ lhs: Self, _ rhs: Self) -> Bool { ... }
    }
    11
    

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12. ࣮૷಺༰ PR apple/swift#28833
    1. ௨ৗͷϓϩτίϧίϯϑΥʔϚϯεͷଞʹ
    BuiltinProtocolConformanceͷ֓೦Λ௥Ճ
    2. ܕਪ࿦ثͷରԠ
    3. ϥϯλΠϜϥΠϒϥϦʹBuiltinProtocolConformanceΛ࣮૷
    4. IRGenͰBuiltinProtocolConformanceΛࢀর͢ΔΑ͏ʹίʔ
    υੜ੒
    ࠓ೔ͷϝΠϯτϐοΫ͸3ͱ4
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13. ⾠ આ໌ͷͨΊɺٙࣅSwiftΛ࢖ͬͨΓɺ࣮ࡍ͸C++Ͱॻ͔Εͨϥ
    ϯλΠϜؔ਺ΛSwiftͰ؆୯ʹॻ͖௚ͨ͠Γͯ͠·͢ɻ
    13
    

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14. ௨ৗͷϓϩτίϧద߹
    WitnessTable͕੩తʹܾ·Δ৔߹
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15. func isEqual(_ lhs: T, _ rhs: T) -> Bool { lhs == rhs }
    _ = isEqual(1, 2) // false
    // ↓తͳײ͡ʹίϯύΠϧ͞ΕΔ
    func isEqual(_ lhs: T, _ rhs: T, type: T.Type, witnessTable: WitnessTable) -> Bool {
    let fn = witnessTable[Equatable.==]
    return fn(lhs, rhs)
    }
    let Int_Equatable_WitnessTable: WitnessTable = [
    Equatable.==: Int.==,
    ]
    _ = isEqual(1, 2, Int.self, Int_Equatable_WitnessTable) // false
    15
    

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16. ௨ৗͷϓϩτίϧద߹
    WitnessTable͕ಈతʹܾ·Δ৔߹
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17. ίϯύΠϧલ
    public struct Box { public let value: T }
    extension Box: CustomStringConvertible where T: CustomStringConvertible {
    var description: String { value.description }
    }
    func stringify(_ target: T) -> String {
    return target.description
    }
    func boxStringify(_ target: T) -> String {
    return stringify(Box(value: target))
    }
    _ = boxStringify(1) // "1"
    17
    

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18. ίϯύΠϧޙ
    func stringify(_ target: T, type: T.Type, witnessTable: WitnessTable) -> String? {
    return witnessTable.description(target)
    }
    func boxStringify(_ target: T, type: T.Type, witnessTable: WitnessTable) -> String {
    let witnessTable = swift_getWitnessTable(Box.self, CustomStringConvertible.self)
    return stringify(Box(value: target), Box.self, witnessTable)
    }
    let Int_CustomStringConvertible_WitnessTable: WitnessTable = [
    CustomStringConvertible.description: Int.description,
    ]
    _ = boxStringify(1, Int.self, Int_CustomStringConvertible_WitnessTable) // "1"
    18
    

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19. swift_conformsToProtocol͸Ͳ͏΍ͬͯWitnessTableΛऔ
    ಘͯ͠Δͷʁ
    // ඪ४ϥΠϒϥϦ
    public protocol CustomStringConvertible { ... }
    public extension Int: CustomStringConvertible { ... }
    let Int_CustomStringConvertible_WitnessTable: WitnessTable = [
    CustomStringConvertible.description: Int.description,
    ]
    let localConformances = [
    Conformance(
    type: Int.self, conforming: CustomStringConvertible.self,
    witnessTable: Int_CustomStringConvertible_WitnessTable
    ),
    ...
    ]
    _registerProtocolConformances(localConformances)
    19
    

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20. // ϥϯλΠϜϥΠϒϥϦ
    var globalConformances: [Conformance] = []
    func _registerProtocolConformances(_ conformances: [Conformance]) {
    globalConformances.append(conformances)
    }
    func swift_getWitnessTable(_ type: Any.Type, _ proto: Protocol.Type) -> WitnessTable? {
    for conformance in globalConformances {
    if conformance.type == type && conformance.conforming == proto {
    return conformance.witnessTable
    }
    }
    return nil
    }
    https://github.com/apple/swift/blob/41f74e4/stdlib/public/runtime/ImageInspectionCommon.cpp 20
    

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21. BuiltinProtocolConformance for λϓϧ
    ͭ·Γɺλϓϧ޲͚ͷWitness TableͱConformanceΛϥϯλΠ
    ϜϥΠϒϥϦʹ࡞͓͚ͬͯ͹ɺ੩త/ಈతͳϢʔεέʔεʹରԠ
    Ͱ͖Δɻ
    21
    

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22. खॻ͖ Tuple.==
    bool swift::_swift_tupleEquatable_equals(OpaqueValue *tuple1, OpaqueValue *tuple2,
    SWIFT_CONTEXT Metadata *swiftSelf, Metadata *Self, void *witnessTable) {
    auto tuple = cast(Self);
    auto table = reinterpret_cast(witnessTable);
    // Loop through all elements, and check if both tuples element is equal.
    for (size_t i = 0; i != tuple->NumElements; i += 1) {
    auto elt = tuple->getElement(i);
    // Get the element conformance from the private data in the witness table.
    auto conformance = reinterpret_cast(table[-1 - i]);
    auto value1 = reinterpret_cast(
    reinterpret_cast(tuple1) + elt.Offset);
    auto value2 = reinterpret_cast(
    reinterpret_cast(tuple2) + elt.Offset);
    // Grab the specific witness for this element type.
    auto equatableTable = reinterpret_cast(conformance);
    auto equalsWitness = equatableTable[WitnessTableFirstRequirementOffset];
    auto equals = reinterpret_cast(equalsWitness);
    // Call the equal function
    auto result = equals(value1, value2, elt.Type, elt.Type, conformance);
    // If the values aren't equal, this tuple isn't equal. :)
    if (!result)
    return false;
    }
    // Otherwise this tuple has value equality with all elements.
    return true;
    }
    https://github.com/apple/swift/pull/28833/files#diff-c289d2fa8030a8b0648018ab48d060bb32554aa01b96399c406702089ef0033cR148-R184 22
    

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23. खॻ͖Protocol Conformance Descriptor
    __asm(
    #if defined(__ELF__)
    " .type __swift_tupleEquatable_private, @object\n"
    " .local __swift_tupleEquatable_private\n"
    " .comm __swift_tupleEquatable_private, 128, 16\n"
    " .protected " TUPLE_EQUATABLE_CONF "\n"
    " .type " TUPLE_EQUATABLE_CONF ", @object\n"
    " .section .rodata\n"
    #elif defined(__MACH__)
    " .zerofill __DATA, __bss, __swift_tupleEquatable_private, 128, 4\n"
    " .section __TEXT, __const\n"
    #elif defined(_WIN32)
    " .lcomm __swift_tupleEquatable_private, 128, 16\n"
    " .section .rdata, \"dr\"\n"
    #pragma comment(linker, "/EXPORT:_swift_tupleEquatable_conf,DATA")
    #endif
    " .globl " TUPLE_EQUATABLE_CONF "\n"
    " .p2align 2\n"
    TUPLE_EQUATABLE_CONF ":\n"
    // This is an indirectable relative reference to the GOT entry for the
    // Equatable protocol descriptor.
    " .long " INDIRECT_RELREF_GOTPCREL(EQUATABLE_DESCRIPTOR_SYMBOL) "\n"
    // 769 is the MetadataKind::Tuple
    " .long 769\n"
    // This indicates that we have no witness table pattern. We use a generic
    // witness table for builtin conformances.
    " .long 0\n"
    // 196640 are the ConformanceFlags with the type reference bit set to
    // MetadataKind, the has resilient witness bit, and the generic witness table
    // bit.
    " .long 196640\n"
    // This 1 is the ResilientWitnessesHeader indicating we have 1 resilient
    // witness.
    " .long 1\n"
    // This is an indirectable relative reference to the GOT entry for the
    // Equatable == method descriptor.
    " .long " INDIRECT_RELREF_GOTPCREL(EQUATABLE_EE_METHOD_DESCRIPTOR) "\n"
    // This is a direct relative reference to the equals witness defined below.
    " .long (" TUPLE_EQUATABLE_EQUALS ") - .\n"
    // The witness table size in words.
    " .short 0\n"
    // The witness table private size in words & requires instantiation.
    " .short 1\n"
    // The witness table instantiator function.
    " .long 0\n"
    // This is a direct relative reference to the private data for the
    // conformance.
    " .long __swift_tupleEquatable_private - .\n"
    #if defined(__ELF__)
    " .size " TUPLE_EQUATABLE_CONF ", 40\n"
    #endif
    );
    23
    

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24. extern "C" const ProtocolConformanceDescriptor _swift_tupleEquatable_conf;
    extern "C" const ProtocolConformanceDescriptor _swift_tupleComparable_conf;
    extern "C" const ProtocolConformanceDescriptor _swift_tupleHashable_conf;
    static const ProtocolConformanceDescriptor *getTupleConformanceDescriptor(
    const ProtocolDescriptor *protocol) {
    if (protocol == &EQUATABLE_DESCRIPTOR) {
    return &_swift_tupleEquatable_conf;
    }
    if (protocol == &COMPARABLE_DESCRIPTOR) {
    return &_swift_tupleComparable_conf;
    }
    if (protocol == &HASHABLE_DESCRIPTOR) {
    return &_swift_tupleHashable_conf;
    }
    return nullptr;
    }
    static const WitnessTable *
    swift_conformsToProtocolImpl(const Metadata *const type,
    const ProtocolDescriptor *protocol) {
    ...
    // If we're asking if a tuple conforms to a protocol, handle that here for
    // builtin conformances.
    if (auto tuple = dyn_cast(type)) {
    if (tupleConformsToProtocol(tuple, protocol)) {
    auto descriptor = getTupleConformanceDescriptor(protocol);
    C.cacheResult(type, protocol, descriptor->getWitnessTable(type),
    /*always cache*/ 0);
    }
    }
    ...
    }
    24
    

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25. ੩తͳProtocol Conformance Descriptorͷࢀর
    std::string IRGenMangler::mangleProtocolConformanceDescriptor(
    const RootProtocolConformance *conformance) {
    // Builtin conformances are different because they don't use a mangled name
    // for their conformance descriptors. For now, we use predefined symbol names
    // just in case in the future we have some conflict between actual
    // conformances and these builtin ones.
    if (isa(conformance)) {
    auto &ctx = conformance->getType()->getASTContext();
    if (conformance->getType()->is()) {
    auto equatable = ctx.getProtocol(KnownProtocolKind::Equatable);
    auto comparable = ctx.getProtocol(KnownProtocolKind::Comparable);
    auto hashable = ctx.getProtocol(KnownProtocolKind::Hashable);
    if (conformance->getProtocol() == equatable) {
    return "_swift_tupleEquatable_conf";
    }
    if (conformance->getProtocol() == comparable) {
    return "_swift_tupleComparable_conf";
    }
    if (conformance->getProtocol() == hashable) {
    return "_swift_tupleHashable_conf";
    }
    llvm_unreachable("mangling conformance descriptor for unknown tuple \
    protocol");
    }
    llvm_unreachable("mangling conformance descriptor for unknown builtin type");
    }
    ...
    }
    25
    

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26. ͕͜͜ਏ͍ΑBuiltinProtocolConformance
    • ݴΘͣ΋͕ͳΠϯϥΠϯΞηϯϒϦ͕ਏ͍
    26
    

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27. ճආࡦ1
    • ίϯύΠϥͰඪ४ϥΠϒϥϦͷͨΊ͚ͩʹίʔυੜ੒͢Δ
    27
    

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28. ճආࡦ2
    • LLVM IRͰॻ͘
    28
    

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