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Swift 进阶（十七）源码分析
来源：cnblogs　　作者：FunkyRay　　时间：2021/4/6 10:05:49　　对本文有异议

我们通过分析Swift标准库源码来更近一步了解Swift的语法

Array相关

map、filter的源码路径:/swift-main/stdlib/public/core/Sequence.swift

flatMap、compactMap、reduce的源码路径:/swift-main/stdlib/public/core/SequenceAlgorithms.swift

map

  1. @inlinable
  2. public func map<T>(
  3. _ transform: (Element) throws -> T
  4. ) rethrows -> [T] {
  6.   let initialCapacity = underestimatedCount
  7.   var result = ContiguousArray<T>()
  8.   result.reserveCapacity(initialCapacity)
  10.   var iterator = self.makeIterator()
  12.   // Add elements up to the initial capacity without checking for regrowth.
  13.   for _ in 0..<initialCapacity {
  14.     result.append(try transform(iterator.next()!))
  15.   }
  16.   
  17.   // Add remaining elements, if any.
  18.   while let element = iterator.next() {
  19.     // 如果element是数组，会把整个数组作为元素加到新数组中
  20.     result.append(try transform(element))
  21.   }
  22.   
  23.   return Array(result)
  24. }

flatMap

  1. @inlinable
  2. public func flatMap<SegmentOfResult: Sequence>(
  3. _ transform: (Element) throws -> SegmentOfResult
  4. ) rethrows -> [SegmentOfResult.Element] {
  6.   var result: [SegmentOfResult.Element] = []
  7.   for element in self {
  8.     // 将数组元素添加到新数组中
  9.     result.append(contentsOf: try transform(element))
  10.   } 
  11.   
  12.   return result
  13. }

filter

  1. @inlinable
  2. public __consuming func filter(
  3. _ isIncluded: (Element) throws -> Bool
  4. ) rethrows -> [Element] {
  5.   return try _filter(isIncluded)
  6. }
  8. @_transparent
  9. public func _filter(
  10. _ isIncluded: (Element) throws -> Bool
  11. ) rethrows -> [Element] {
  13.   var result = ContiguousArray<Element>()
  15.   var iterator = self.makeIterator()
  17.   while let element = iterator.next() {
  18.     if try isIncluded(element) {
  19.       result.append(element)
  20.     }
  21.   }
  23.   return Array(result)
  24. }

compactMap

  1. @inlinable // protocol-only
  2. public func compactMap<ElementOfResult>(
  3. _ transform: (Element) throws -> ElementOfResult?
  4. ) rethrows -> [ElementOfResult] {
  5.   return try _compactMap(transform)
  6. }
  8. @inlinable // protocol-only
  9. @inline(__always)
  10. public func _compactMap<ElementOfResult>(
  11. _ transform: (Element) throws -> ElementOfResult?
  12. ) rethrows -> [ElementOfResult] {
  14.   var result: [ElementOfResult] = []
  15.   
  16.   for element in self {
  17.     // 会进行解包，只有不为空才会被加到数组中
  18.     if let newElement = try transform(element) {
  19.       result.append(newElement)
  20.     }
  21.   }
  22.   
  23.   return result
  24. }

reduce

  1. @inlinable
  2. public func reduce<Result>(
  3. _ initialResult: Result,
  4. _ nextPartialResult:
  5. (_ partialResult: Result, Element) throws -> Result
  6. ) rethrows -> Result {
  8.   // 上一次的结果
  9.   var accumulator = initialResult
  10.     
  11.   for element in self {
  12.     accumulator = try nextPartialResult(accumulator, element)
  13.   }
  14.   
  15.   return accumulator
  16. }

Substring相关

Substring的源码路径:/swift-main/stdlib/public/core/Substring.swift

初始化

  1. @frozen
  2. public struct Substring: ConcurrentValue {
  3.   @usableFromInline
  4.   internal var _slice: Slice<String>
  6.   @inlinable
  7.   internal init(_ slice: Slice<String>) {
  8.     let _guts = slice.base._guts
  9.     let start = _guts.scalarAlign(slice.startIndex)
  10.     let end = _guts.scalarAlign(slice.endIndex)
  11.     
  12.     // 保存传进来的字符串的内容和位置
  13.     self._slice = Slice(
  14.       base: slice.base,
  15.       bounds: Range(_uncheckedBounds: (start, end))) 
  16.     _invariantCheck()
  17.   }
  19.   @inline(__always)
  20.   internal init(_ slice: _StringGutsSlice) {
  21.     self.init(String(slice._guts)[slice.range])
  22.   }
  24.   /// Creates an empty substring.
  25.   @inlinable @inline(__always)
  26.   public init() {
  27.     self.init(Slice())
  28.   }
  29. }
  31. extension Substring {
  32.   /// Returns the underlying string from which this Substring was derived.
  33.   @_alwaysEmitIntoClient
  34.   
  35.   // _slice.base就是初始化传进来的字符串
  36.   public var base: String { return _slice.base }
  38.   @inlinable @inline(__always)
  39.   internal var _wholeGuts: _StringGuts { return base._guts }
  41.   @inlinable @inline(__always)
  43.   // 从这里也能看出和传进来的String共有的是同一块区域，在这块区域进行偏移获取Substring的内容
  44.   internal var _offsetRange: Range<Int> {
  45.     return Range(
  46.       _uncheckedBounds: (startIndex._encodedOffset, endIndex._encodedOffset))
  47.   }
  49.   #if !INTERNAL_CHECKS_ENABLED
  50.   @inlinable @inline(__always) internal func _invariantCheck() {}
  51.   #else
  52.   @usableFromInline @inline(never) @_effects(releasenone)
  53.   internal func _invariantCheck() {
  54.     // Indices are always scalar aligned
  55.     _internalInvariant(
  56.       _slice.startIndex == base._guts.scalarAlign(_slice.startIndex) &&
  57.       _slice.endIndex == base._guts.scalarAlign(_slice.endIndex))
  59.     self.base._invariantCheck()
  60.   }
  61.   #endif // INTERNAL_CHECKS_ENABLED
  62. }

append

  1. extension Substring: RangeReplaceableCollection {
  2.   @_specialize(where S == String)
  3.   @_specialize(where S == Substring)
  4.   @_specialize(where S == Array<Character>)
  5.   public init<S: Sequence>(_ elements: S)
  6.   where S.Element == Character {
  7.     if let str = elements as? String {
  8.       self.init(str)
  9.       return
  10.     }
  11.     if let subStr = elements as? Substring {
  12.       self = subStr
  13.       return
  14.     }
  15.     self.init(String(elements))
  16.   }
  18.   // Substring的拼接
  19.   @inlinable // specialize
  20.   public mutating func append<S: Sequence>(contentsOf elements: S)
  21.   where S.Element == Character {
  23. 		// 拼接时会创建一个新的字符串
  24.     var string = String(self)
  25.     self = Substring() // Keep unique storage if possible
  26.     string.append(contentsOf: elements)
  27.     self = Substring(string)
  28.   }
  29. }

lowercased、uppercased

  1. extension Substring {
  2.   public func lowercased() -> String {
  3.     return String(self).lowercased()
  4.   }
  6.   public func uppercased() -> String {
  7.     return String(self).uppercased()
  8.   }
  10.   public func filter(
  11.     _ isIncluded: (Element) throws -> Bool
  12.   ) rethrows -> String {
  13.     return try String(self.lazy.filter(isIncluded))
  14.   }
  15. }

Optional相关

Optional的源码路径:/swift-main/stdlib/public/core/Optional.swift

map

  1. @inlinable
  2. public func map<U>(
  3. _ transform: (Wrapped) throws -> U
  4. ) rethrows -> U? {
  5.   switch self {
  6.   case .some(let y): // 先解包进行处理
  7.     return .some(try transform(y)) // 然后再包装一层可选类型返回出去
  8.   case .none:
  9.     return .none
  10.   }
  11. }

flatMap

  1. @inlinable
  2. public func flatMap<U>(
  3. _ transform: (Wrapped) throws -> U?
  4. ) rethrows -> U? {
  5.   switch self {
  6.   case .some(let y): // 先进行解包
  7.     return try transform(y) // 将解包后的处理完直接给出去
  8.   case .none:
  9.     return .none
  10.   }
  11. }

==

==两边都为可选项

  1. @inlinable
  2. public static func ==(lhs: Wrapped?, rhs: Wrapped?) -> Bool {
  3.   switch (lhs, rhs) {
  4.     case let (l?, r?):
  5.       return l == r
  6.     case (nil, nil):
  7.       return true
  8.     default:
  9.       return false
  10.   }
  11. }

==左边为可选项，右边为nil

  1. @_transparent
  2. public static func ==(lhs: Wrapped?, rhs: _OptionalNilComparisonType) -> Bool {
  3.   switch lhs {
  4.     case .some:
  5.       return false
  6.     case .none:
  7.       return true
  8.   }
  9. }

==左边为nil，右边为可选项

  1. @_transparent
  2. public static func ==(lhs: _OptionalNilComparisonType, rhs: Wrapped?) -> Bool {
  3.   switch rhs {
  4.     case .some:
  5.       return false
  6.     case .none:
  7.       return true
  8.   }
  9. }

_OptionalNilComparisonType是一个遵守ExpressibleByNilLiteral协议的结构体，可以用nil来进行初始化

  1. // 遵守ExpressibleByNilLiteral协议的结构体，可以用nil来进行初始化
  2. @frozen
  3. public struct _OptionalNilComparisonType: ExpressibleByNilLiteral {
  4.   /// Create an instance initialized with `nil`.
  5.   @_transparent
  6.   public init(nilLiteral: ()) {
  7.   }
  8. }

??

  1. @_transparent
  2. public func ?? <T>(optional: T?, defaultValue: @autoclosure () throws -> T)
  3.     rethrows -> T {
  4.   switch optional {
  5.   case .some(let value):
  6.     return value
  7.   case .none:
  8.     return try defaultValue()
  9.   }
  10. }
  1. @_transparent
  2. public func ?? <T>(optional: T?, defaultValue: @autoclosure () throws -> T?)
  3.     rethrows -> T? {
  4.   switch optional {
  5.   case .some(let value):
  6.     return value
  7.   case .none:
  8.     return try defaultValue()
  9.   }
  10. }

Metadata相关

源码路径:

/swift-main/include/swift/ABI/Metadata.h
/swift-main/include/swift/ABI/MetadataKind.def
/swift-main/include/swift/ABI/MetadataValues.h
/swift-main/include/swift/Reflection/Records.h

文档路径:

/swift-main/docs/ABI/TypeMetadata.rst

Swift中很多类型都有自己的metadata

-w1020

Class Metadata

我们可以从第三方库KaKaJSON中的ClassType，以及对应Metadata的相关文档来分析Class Metadata信息

  1. struct ClassLayout: ModelLayout {
  2.     let kind: UnsafeRawPointer
  3.     
  4.     /// 指向父类类型的指针
  5.     let superclass: Any.Type
  6.     
  7.     /// The cache data is used for certain dynamic lookups; it is owned by the runtime and generally needs to interoperate with Objective-C's use
  8.     /// 缓存数据用于某些动态查找；它属于运行时，通常需要与Objective-C的使用进行互操作
  9.     let runtimeReserved0: UInt
  10.     let runtimeReserved1: UInt
  11.     
  12.     /// The data pointer is used for out-of-line metadata and is generally opaque, except that the compiler sets the low bit in order to indicate that this is a Swift metatype and therefore that the type metadata header is present
  13.     let rodata: UInt
  14.     
  15.     /// Swift-specific class flags
  16.     /// 类标志
  17.     let flags: UInt32
  18.     
  19.     /// The address point of instances of this type
  20.     /// 实例的地址值
  21.     let instanceAddressPoint: UInt32
  23.     /// The required size of instances of this type. 'InstanceAddressPoint' bytes go before the address point; 'InstanceSize - InstanceAddressPoint' bytes go after it
  24.     /// 实例大小
  25.     let instanceSize: UInt32
  27.     /// The alignment mask of the address point of instances of this type
  28.     /// 实例对齐掩码
  29.     let instanceAlignMask: UInt16
  31.     /// Reserved for runtime use
  32.     /// 运行时保留字段
  33.     let reserved: UInt16
  35.     /// The total size of the class object, including prefix and suffix extents
  36.     /// 类对象的大小
  37.     let classSize: UInt32
  39.     /// The offset of the address point within the class object
  40.     /// 类对象地址
  41.     let classAddressPoint: UInt32
  43.     // Description is by far the most likely field for a client to try to access directly, so we force access to go through accessors
  44.     /// An out-of-line Swift-specific description of the type, or null if this is an artificial subclass.  We currently provide no supported mechanism for making a non-artificial subclass dynamically
  45.     var description: UnsafeMutablePointer<ClassDescriptor>
  46.     
  47.     /// A function for destroying instance variables, used to clean up after an early return from a constructor. If null, no clean up will be performed and all ivars must be trivial
  48.     let iVarDestroyer: UnsafeRawPointer
  49.     
  50.     var genericTypeOffset: Int {
  51.         let descriptor = description.pointee
  52.         // don't have resilient superclass
  53.         if (0x4000 & flags) == 0 {
  54.             return (flags & 0x800) == 0
  55.             ? Int(descriptor.metadataPositiveSizeInWords - descriptor.numImmediateMembers)
  56.             : -Int(descriptor.metadataNegativeSizeInWords)
  57.         }
  58.         return GenenicTypeOffset.wrong
  59.     }
  60. }

原文链接：http://www.cnblogs.com/funkyRay/p/swift-jin-jie-shi-qi-yuan-ma-fen-xi.html

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