掀起 SWIFT 的面紗

讓我們一起探討 Swift Standard Library 與一些基本型別、集合的幕後原理。

Talking about some basic type and collection in Swift Standard Library.

Transcript

1. 掀起 SWIFT 的⾯面紗 下班⾃我進修裝屌指南 Pofat @ iPlayground
2. 我是 Pofat
3. Clone 過 Android Source Code 嗎 讀過 Android Source Code 嗎？ 對 Android Source Code 有什什麼感想? 起源
4. Swift Source Code 對⼯工作的幫助 0%
5. 如何開始 # Install cmake and ninja brew install cmake ninja mkdir swift-source cd swift-source # Clone Swift project to local git clone https://github.com/apple/swift.git ${ROOT} : swift-source here
6. 如何開始 - utils
7. # use update-checkout update all required repos ./swift/utils/update-checkout —clone
8. Compile 前準備
9. Compile! # Partially debug message ./swift/utils/build-script --release-debuginfo # Partially debug message ./swift/utils/build-script --debug # Partially debug message ./swift/utils/build-script --release
10. 檔案架構
11. 檔案架構 # build path (bin, gyb result, tests…) ${ROOT}/build/Ninja-RelWithDebInfoAssert/ swift-macosx-x86_64 # executables ${ROOT}/build/Ninja-RelWithDebInfoAssert/ swift-macosx-x86_64/bin ${BUILD_ROOT} : ${ROOT}/build/Ninja-RelWithDebInfoAssert/ swift-macosx-x86_64/
12. 檔案架構 # Original source file ${ROOT}/swift/stdlib/public/core # Converted swift files from gyb ${ROOT}/build/Ninja-RelWithDebInfoAssert/ swift-macosx-x86_64/stdlib/public/core/8
13. GYB? gyb --line-directive '' -o 
 /path/to/Some.swift Some.swift.gyb
14. @_fixed_layout public struct UInt8 : FixedWidthInteger, UnsignedInteger, _ExpressibleByBuiltinIntegerLiteral { /// A type that represents an integer literal. public typealias IntegerLiteralType = UInt8 @_transparent public init(_builtinIntegerLiteral x: _MaxBuiltinIntegerType) { _value = Builtin.s_to_u_checked_trunc_Int2048_Int8(x).0 } @_transparent public init(bitPattern x: Int8) { _value = x._value }
15. Tuple let a = (1, 2, 3, 4, 5, 6) let b = (1, 2, 3, 4, 5, 6) print("a == b ? \(a == b)") a == b ? true
16. Tuple let c = (1, 2, 3, 4, 5, 6, 7) let d = (1, 2, 3, 4, 5, 6, 7) print("c == d ? \(c == d)") error: binary operator '==' cannot be applied to two '(Int, Int, Int, Int, Int, Int, Int)' operands
17. Tuple’s GYB % for arity in range(2,7): % typeParams = [chr(ord("A") + i) for i in range(arity)] % tupleT = "({})".format(",".join(typeParams)) % equatableTypeParams = ", ".join(["{} : Equatable".format(c) for c in typeParams]) % originalTuple = "(\"a\", {})".format(", ".join(map(str, range(1, arity)))) % greaterTuple = "(\"a\", {})".format(", ".join(map(str, range(1, arity - 1) + [arity]))) // Tuple.swift.gyb
18. public func == <A : Comparable, B : Comparable, C : Comparable, D : Comparable, E : Comparable, F : Comparable>(lhs: (A,B,C,D,E,F), rhs: (A,B,C,D,E,F)) -> Bool {
 guard lhs.0 == rhs.0 { return false } return ( lhs.1, lhs.2, lhs.3, lhs.4, lhs.5 ) == ( rhs.1, rhs.2, rhs.3, rhs.4, rhs.5 )
 
 } // Tuple.swift
19. Optional @_frozen public enum Optional<Wrapped> : ExpressibleByNilLiteral { case none case some(Wrapped) @_transparent public init(_ some: Wrapped) { self = .some(some) } @_transparent public init(nilLiteral: ()) { self = .none } }
20. Optional - Map public func map<U>( _ transform: (Wrapped) throws -> U ) rethrows -> U? {
 switch self { case .some(let y): return .some(try transform(y)) case .none: return .none } }
21. Optional - flatMap public func flatMap<U>( _ transform: (Wrapped) throws -> U ) rethrows -> U? {
 switch self { case .some(let y): return try transform(y) case .none: return .none } }
22. Optional - Unwrap @_transparent public func ?? <T>(optional: T?, defaultValue: @autoclosure () throws -> T?) rethrows -> T? { switch optional { case .some(let value): return value case .none: return try defaultValue() } }
23. Bool @_fixed_layout public struct Bool { @usableFromInline internal var _value: Builtin.Int1 public init() { let zero: Int8 = 0 self._value = Builtin.trunc_Int8_Int1(zero._value) } }
24. ExpressibleByBooleanLiteral extension Bool: ExpressibleByBooleanLiteral { @_transparent public init(booleanLiteral value: Bool) { self = value } }
25. How to @autoclosure if measurement.count > 0 && sum / Double(measurement.count) < 5 { // do somehting.. } measurement.count might be ZERO!!
26. How to @autoclosure @_transparent @inline(__always) public static func && ( lhs: Bool, rhs: @autoclosure () throws -> Bool) rethrows -> Bool { return lhs ? try rhs() : false }
27. Attributes • @inlinable ：expose not interface but source code, work when -O • @_transparent: must do inline even when -Onone • @_fixed_layout: Processed at SIL stage. It tells compiler that access properties by offset is possible without looking up metadata.
 

28. Attributes • @usableFromInline : Temporarily change scope only during inline stage. Include @inlinable
 
 
 
 
 
 
 
 @_fixed_layout public struct Bool { @usableFromInline internal var _value: Builtin.Int1 // …
29. What is Builtin ? Builtin.Int1
 Builtin.trunc_Int8_Int1(zero._value) 
 
 Builtin.s_to_u_checked_trunc_Int2048_Int8(x)
30. Integer Again public struct Int : FixedWidthInteger, SignedInteger, _ExpressibleByBuiltinIntegerLiteral { 
 public init(_builtinIntegerLiteral x: _MaxBuiltinIntegerType) { _value = Builtin.s_to_s_checked_trunc_Int2048_Int64(x).0 }
31. + public static func +(lhs: Int, rhs: Int) -> Int { var lhs = lhs lhs += rhs return lhs }
32. += public static func +=(lhs: inout Int, rhs: Int) { let (result, overflow) = Builtin.sadd_with_overflow_Int64( lhs._value, rhs._value, true._value) Builtin.condfail(overflow) lhs = Int(result) }
33. You may surprise… • Int is a struct in standard library • + is a global function declared in standard library • What an inefficient way !! Do we really implement basic arithmetic operations by cross-module function calls?
 

35. ObjC & Swift Compilation Clang Frontend ObjC LLVM LLVM IR Machine Code Swift Frontend Swift IRGen SIL Machine Code LLVM LLVM IR
36. Example // sum.swift let a = 1 let b = 2 let c = a + b $swiftc -emit-ir sum.swift
37. LLVM IR define i32 @main(i32, i8**) #0 { entry: %2 = bitcast i8** %1 to i8* store i64 1, i64* getelementptr inbounds (%TSi, %TSi* @"$S4test1aSivp", i32 0, i32 0), align 8 store i64 2, i64* getelementptr inbounds (%TSi, %TSi* @"$S4test1bSivp", i32 0, i32 0), align 8 %3 = load i64, i64* getelementptr inbounds (%TSi, %TSi* @"$S4test1aSivp", i32 0, i32 0), align 8 %4 = load i64, i64* getelementptr inbounds (%TSi, %TSi* @"$S4test1bSivp", i32 0, i32 0), align 8 %5 = call { i64, i1 } @llvm.sadd.with.overflow.i64(i64 %3, i64 %4) %6 = extractvalue { i64, i1 } %5, 0 %7 = extractvalue { i64, i1 } %5, 1 br i1 %7, label %9, label %8
38. llvm::Intrinsic::ID swift::getLLVMIntrinsicIDForBuiltinWithOverflow(BuiltinValue Kind ID) { switch (ID) { default: break; case BuiltinValueKind::SAddOver: return llvm::Intrinsic::sadd_with_overflow; case BuiltinValueKind::UAddOver: return llvm::Intrinsic::uadd_with_overflow; case BuiltinValueKind::SSubOver: return llvm::Intrinsic::ssub_with_overflow; case BuiltinValueKind::USubOver: return llvm::Intrinsic::usub_with_overflow; case BuiltinValueKind::SMulOver: return llvm::Intrinsic::smul_with_overflow; case BuiltinValueKind::UMulOver: return llvm::Intrinsic::umul_with_overflow; } llvm_unreachable("Cannot convert the overflow builtin to llvm intrinsic."); } ${ROOT}/swift/lib/AST/Builtin.cpp
39. Builtin is a portal LLVM IR Builtin Builtin.type Builtin.method Standard Library TYPE METHOD SIL stage
40. How To Use Builtin. // builtin_add.swift import Swift let (result, overflow) = Builtin.sadd_with_overflow_Int64(1._value, 2._value, true._getBuiltinLogicValue()) print(Int(result)) $swiftc -parse-stdlib builtin_add.swift && ./builtin_add
41. @usableFromInline // builtin_add.swift import Swift let (result, overflow) = Builtin.sadd_with_overflow_Int64(1._value, 2._value, true._value) print(Int(result)) error: '_value' is inaccessible due to 'internal' protection level
42. Sequence https://swiftdoc.org/v4.2/protocol/sequence/hierarchy/
43. Sequence public protocol Sequence { associatedtype Element associatedtype Iterator : IteratorProtocol where Iterator.Element == Element func makeIterator() -> Iterator }
 public protocol IteratorProtocol { mutating func next() -> Element? }
44. Sequence public protocol Sequence { associatedtype Element associatedtype Iterator : IteratorProtocol where Iterator.Element == Element func makeIterator() -> Iterator }
 public protocol IteratorProtocol { mutating func next() -> Element? }
45. for (index, value) in mySeq.enumerated() { // do seomthing ... } O(1)
46. Enumerated /// - Complexity: O(1) @inlinabl public func enumerated() -> EnumeratedSequence<Self> { return EnumeratedSequence(_base: self) }
47. Enumerated public struct EnumeratedSequence<Base: Sequence> { internal var _base: Base internal init(_base: Base) { self._base = _base } }
48. for-in EnumeratedSequence extension EnumeratedSequence { public struct Iterator { internal var _base: Base.Iterator internal var _count: Int internal init(_base: Base.Iterator) { self._base = _base self._count = 0 } } }
49. for-in EnumeratedSequence extension EnumeratedSequence.Iterator: IteratorProtocol, Sequence { public typealias Element = (offset: Int, element: Base.Element) public mutating func next() -> Element? { guard let b = _base.next() else { return nil } let result = (offset: _count, element: b) _count += 1 return result } }
50. Map public func map<T>( _ transform: (Element) throws -> T ) rethrows -> [T] {
 let initialCapacity = underestimatedCount var result = ContiguousArray<T>() result.reserveCapacity(initialCapacity) var iterator = self.makeIterator() // lower half of map func
51. Map // upper half of map func for _ in 0..<initialCapacity { result.append(try transform(iterator.next()!)) } while let element = iterator.next() { result.append(try transform(element)) } return Array(result) }
52. Reduce public func reduce<Result>( _ initialResult: Result, _ nextPartialResult: (_ partialResult: Result, Element) throws -> Result ) rethrows -> Result {
 var accumulator = initialResult for element in self { accumulator = try nextPartialResult(accumulator, element) }
 return accumulator }
53. Reduce Into public func reduce<Result>( into initialResult: Result, _ updateAccumulatingResult: (_ partialResult: inout Result, Element) throws -> () ) rethrows -> Result { var accumulator = initialResult for element in self { try updateAccumulatingResult(&accumulator, element) } return accumulator } }
54. flatMap public func flatMap<SegmentOfResult : Sequence>( _ transform: (Element) throws -> SegmentOfResult ) rethrows -> [SegmentOfResult.Element] {
 var result: [SegmentOfResult.Element] = [] for element in self { result.append(contentsOf: try transform(element)) }
 return result }
55. compactMap public func compactMap<ElementOfResult>( _ transform: (Element) throws -> ElementOfResult? ) rethrows -> [ElementOfResult] {
 return try _compactMap(transform)
 }
56. public func _compactMap<ElementOfResult>( _ transform: (Element) throws -> ElementOfResult? ) rethrows -> [ElementOfResult] {
 var result: [ElementOfResult] = []
 for element in self { if let newElement = try transform(element) { result.append(newElement) } }
 return result }
57. They are EAGER
58. class FileReadIterator: IteratorProtocol { 
 private let handler = FileHandle(forReadingAtPath: "/path/to/large_file")! func next() -> UInt8? { let data = handler.readData(ofLength: 1) return data[0] } 
 deinit { handler.closeFile() } }
59. let fileSequence = AnySequence { FileReadIterator() }
 let batchOperation = fileSequence.map{ print($0) }
60. Make It LAZY
61. Lazy Sequence extension Sequence {
 public var lazy: LazySequence<Self> { return LazySequence(_base: self) }
 }
62. LazySequence public struct LazySequence<Base : Sequence>: _SequenceWrapper {
 public var _base: Base internal init(_base: Base) { self._base = _base } }
63. LazySequenceProtocol extension LazySequenceProtocol { public func map<U>( _ transform: @escaping (Elements.Element) -> U ) -> LazyMapSequence<Self.Elements, U> { return LazyMapSequence(_base: self.elements, transform: transform) } }
64. public struct LazyMapSequence<Base : Sequence, Element> { internal var _base: Base internal let _transform: (Base.Element) -> Element internal init(_base: Base, transform: @escaping (Base.Element) -> Element) {
 self._base = _base self._transform = transform
 } }
65. extension LazyMapSequence.Iterator: IteratorProtocol, Sequence { public mutating func next() -> Element? {
 return _base.next().map(_transform)
 } }
66. File Reader Revised let fileSequence = AnySequence { FileReadIterator() }
 let lazyBatch = fileSequence.lazy.map{ print($0)} var batchIterator = lazyBatch.makeIterator() for _ in 1 ... 10 { batchIterator.next() }
67. File Reader Revised let fileSequence = AnySequence { FileReadIterator() }
 let lazyBatch = fileSequence.lazy.map{ print($0)} var batchIterator = lazyBatch.makeIterator() for _ in 1 ... 1024 { batchIterator.next() }
68. Collection https://swiftdoc.org/v4.2/protocol/collection/hierarchy/
69. Collection remove(at:) problem for obj in objsToDelete { myCollection.remove(at: myCollection.index(of: obj)!) } O(N)
70. Collection removeAll(where:) extension RangeReplaceableCollection {
 public mutating func removeAll( where shouldBeRemoved: (Element) throws -> Bool ) rethrows {
 let suffixStart = try _halfStablePartition(isSuffixElement: shouldBeRemoved)
 removeSubrange(suffixStart…) } }
71. mutating func _halfStablePartition( isSuffixElement: (Element) throws -> Bool ) rethrows -> Index {
 guard var i = try firstIndex(where: isSuffixElement) else { return endIndex } var j = index(after: i) while j != endIndex { if try !isSuffixElement(self[j]) { swapAt(i, j); formIndex(after: &i) } formIndex(after: &j) }
 return i }
72. mutating func _halfStablePartition( isSuffixElement: (Element) throws -> Bool ) rethrows -> Index {
 guard var i = try firstIndex(where: isSuffixElement) else { return endIndex } var j = index(after: i)
 while j != endIndex { if try !isSuffixElement(self[j]) { swapAt(i, j) formIndex(after: &i) } formIndex(after: &j) }
 return i } OH! It’s moving zeros!
73. Array
74. Inside Array public struct Array<Element>: _DestructorSafeContainer { #if _runtime(_ObjC) internal typealias _Buffer = _ArrayBuffer<Element> #endif internal var _buffer: _Buffer internal init(_buffer: _Buffer) { self._buffer = _buffer } }
75. struct Array _buffer struct _ArrayBuffer _storage struct _BridgStorage _rawValue Contiguous Array
 or NSArray Builtin.BridgeObject
77. Copy On Write mutating func append(_ newElement: __owned Element) { _makeUniqueAndReserveCapacityIfNotUnique()
 let oldCount = _getCount() _reserveCapacityAssumingUniqueBuffer(oldCount: oldCount)
 _appendElementAssumeUniqueAndCapacity(oldCount, newElement: newElement) }
78. Copy If Not Unique mutating func _makeUniqueAndReserveCapacityIfNotUnique() { if _slowPath(! _buffer.isMutableAndUniquelyReferenced()) { _copyToNewBuffer(oldCount: _buffer.count) } }
79. isUnique mutating func isMutableAndUniquelyReferenced() -> Bool { return isUniquelyReferenced() }

80. isUnique mutating func isUniquelyReferenced() -> Bool {
 if !_isClassOrObjCExistential(Element.self) { return _storage.isUniquelyReferenced_native_noSpareBits() } if !_storage.isUniquelyReferencedNative() { return false }
 return _isNative }

81. Copy To New Buffer mutating func _copyToNewBuffer(oldCount: Int) { let newCount = oldCount + 1 var newBuffer = _buffer._forceCreateUniqueMutableBuffer( countForNewBuffer: oldCount, minNewCapacity: newCount) _buffer._arrayOutOfPlaceUpdate(&newBuffer, oldCount, 0) }
82. What If Reach Full Capacity func _forceCreateUniqueMutableBufferImpl( countForBuffer: Int, minNewCapacity: Int, requiredCapacity: Int ) -> _ContiguousArrayBuffer<Element> { let minimumCapacity = Swift.max(requiredCapacity, minNewCapacity > capacity ? _growArrayCapacity(capacity) : capacity) return _ContiguousArrayBuffer( _uninitializedCount: countForBuffer, minimumCapacity: minimumCapacity) }
83. Array Grow func _growArrayCapacity(_ capacity: Int) -> Int { return capacity * 2 }
84. Array Is Not Thread Safe import Dispatch var array = [Int]() DispatchQueue.concurrentPerform(iterations: 50) { index in let last = array.last ?? 0 array.append(last + 1) } print("array count: \(array.count)")
85. var array = [1, 2, 3, 4, 5] let arrayAccessQueue = DispatchQueue(label: "array", qos: .utility, attributes: .concurrent) // read var readValue: Int = 0 arrayAccessQueue.sync { readValue = array[0] } // write arrayAccessQueue.async(flags: .barrier) { array.append(6) } // thread_safe_access_array.swift
86. Sorting Array mutating func sort( by areInIncreasingOrder: (Element, Element) throws -> Bool ) rethrows { let didSortUnsafeBuffer = try _withUnsafeMutableBufferPointerIfSupported { buffer -> Void? in try buffer.sort(by: areInIncreasingOrder) } if didSortUnsafeBuffer == nil { try _introSort(within: startIndex..<endIndex, by: areInIncreasingOrder) } }
87. Insertion / Intro / Heap mutating func _introSortImpl( within range: Range<Index>, by areInIncreasingOrder: (Element, Element) throws -> Bool, depthLimit: Int ) rethrows { if distance(from: range.lowerBound, to: range.upperBound) < 20 { try _insertionSort(within: range, by: areInIncreasingOrder) } else if depthLimit == 0 { try _heapSort(within: range, by: areInIncreasingOrder) } else { let partIdx = try _partition(within: range, by: areInIncreasingOrder) try _introSortImpl( within: range.lowerBound..<partIdx, by: areInIncreasingOrder, depthLimit: depthLimit &- 1) try _introSortImpl( within: partIdx..<range.upperBound, by: areInIncreasingOrder, depthLimit: depthLimit &- 1) } }
88. Sorting Strategy mutating func _introSortImpl( within range: Range<Index>, by areInIncreasingOrder: (Element, Element) throws -> Bool, depthLimit: Int ) rethrows { if distance(from: range.lowerBound, to: range.upperBound) < 20 { try _insertionSort(within: range, by: areInIncreasingOrder) } else if depthLimit == 0 { try _heapSort(within: range, by: areInIncreasingOrder) } else { let partIdx = try _partition(within: range, by: areInIncreasingOrder) try _introSortImpl( within: range.lowerBound..<partIdx, by: areInIncreasingOrder, depthLimit: depthLimit &- 1) try _introSortImpl( within: partIdx..<range.upperBound, by: areInIncreasingOrder, depthLimit: depthLimit &- 1) } }
89. Sorting Strategy mutating func _introSortImpl( within range: Range<Index>, by areInIncreasingOrder: (Element, Element) throws -> Bool, depthLimit: Int ) rethrows { if distance(from: range.lowerBound, to: range.upperBound) < 20 { try _insertionSort(within: range, by: areInIncreasingOrder) } else if depthLimit == 0 { try _heapSort(within: range, by: areInIncreasingOrder) } else { let partIdx = try _partition(within: range, by: areInIncreasingOrder) try _introSortImpl( within: range.lowerBound..<partIdx, by: areInIncreasingOrder, depthLimit: depthLimit &- 1) try _introSortImpl( within: partIdx..<range.upperBound, by: areInIncreasingOrder, depthLimit: depthLimit &- 1) } }
90. Develop Swift !! Better Reduce: User first element in sequence as initial value
91. Test FIRST!
92. SequenceTypeTests.test("betterReduce") { let animals = ["Antelope", "Butterfly", "Camel", “Dolphin"] var timesClosureWasCalled = 0 let longestAnimal = animals.betterReduce { current, animal in timesClousreWasCalled += 1 if current.count > animal.count { return current } else { return animal } } ?? “" // expects … } // ${ROOT}/swift/validation-test/stdlib/SequenceType.swift.gyb
93. SequenceTypeTests.test("betterReduce") { // Codes … expectEqual(longestAnimal, “Butterfly") expectEqual( animals.count, timesClosureWasCalled, "betterReduce() should be eager”) } // ${ROOT}/swift/validation-test/stdlib/SequenceType.swift.gyb
94. Now CODE!!
95. // SequenceAlgorithm.swift — extension Sequence @inlinable public func betterReduce( _ nextPartialResult: (_ partialResult: Element, Element) throws -> Element ) rethrows -> Element? {
 var i = makeIterator() guard var accumulated = i.next() else { return nil } while let element = i.next() { accumulated = try nextPartialResult(accumulated, element) } return accumulated }
96. Test Swift!! ./swift/utils/build-script -r -t Compile and test ./swift/utils/build-script -r -T Compile and validation test 4XXX tests!! 10000+ tests!!
97. Test Standard Library Only ./llvm/utils/lit/lit.py -sv ${BUILD_ROOT}/swift- macosx-x86_64/test-macosx-x86_64/stdlib A full-test run is suggested in the first place ./llvm/utils/lit/lit.py -sv ${BUILD_ROOT}/ swift-macosx-x86_64/validation-test-macosx- x86_64/stdlib
99. sh ${BUILD_ROOT}/validation-test-macosx-x86_64/stdlib/Output/ Bool.swift.script Now you can do single test with
100. Wait! Not compiled yet…
101. ${BUILD_ROOT} ninja swift-stdlib Thanks to ninja, lets build standard library only sh ${BUILD_RTTO}/validation-test-macosx-x86_64/
 stdlib/Output/SequenceType.swift.gyb.script And do test!!
104. 所以，看 Source Code 到底有何幫助？？
106. 參參考來來源 • https://github.com/apple/swift • 喵神 Swift 标准库源码导读
107. 我的裝屌指南系列列 • EP I: GitHub 裝屌指南 • EP II: Vim 裝屌指南 • EP III: Debug 裝屌指南
108. 講完惹 關愛 Swift 發展者或想討論 ，歡迎和我聯聯繫 tjazzterATgmailDOTcom