在 String 里,用来索引 Character 的,不是整数,而是StringIndex 内部结构 extension String { /// A position of a character or code unit in a string. @_fixed_layout public struct Index { @usableFromInline internal var _rawBits: UInt64 @inlinable @inline(__always) init(_ ra…

 small string, 只有两个 UInt64 的字,这里面存储了所有的信息. 内存布局如下:  第二个 UInt64 存储了标记位和长度信息,以及部分字符串的值 // Get an integer equivalent to the _StringObject.discriminatedObjectRawBits // computed property. @inlinable @inline(__always) internal var rawDiscriminatedObject…

以append操作为例 public mutating func append(_ other: String) { if self.isEmpty && !_guts.hasNativeStorage { self = other return } self._guts.append(other._guts) } _StringGuts 做了实际的工作 下面是实际进行append的地方 internal mutating func append(_ slicedOther: _Strin…

Native strings have tail-allocated storage, which begins at an offset of nativeBias from the storage object's address. String literals, which reside in the constant section, are encoded as their start address minus nativeBias, unifying code paths for…

对于普通的字符串,对应的_StringObject 有两个存储属性: _countAndFlagsBits: UInt64 _object: Builtin.BridgeObject _countAndFlagsBits 存储者字符串的长度和一些标记位. ┌─────────┬───────┬──────────────────┬─────────────────┬────────┬───────┐ │ b63 │ b62 │ b61 │ b60 │ b59:48 │ b47:0 │ ├────…

感受一下字符串相关的源文件个数  String 概览 是一个结构体 只有一个变量,类型是 _StringGuts  如上所示,String 真正的内容在__StringStorage或者__SharedStringStorage里面. private static func create( realCodeUnitCapacity: Int, countAndFlags: CountAndFlags ) -> __StringStorage { let storage = Builtin.a…

Given an encoded string, return it's decoded string. The encoding rule is: k[encoded_string], where the encoded_stringinside the square brackets is being repeated exactly k times. Note that kis guaranteed to be a positive integer. You may assume that…

即以 UTF16 编码的格式来查看字符串. UTF16View 是一个结构体 @_fixed_layout public struct UTF16View { @usableFromInline internal var _guts: _StringGuts @inlinable internal init(_ guts: _StringGuts) { self._guts = guts _invariantCheck() } } UTF16View 遵守 BidirectionalCollec…

Shared strings do not have tail-allocated storage, but can provide access upon query to contiguous UTF-8 code units. Lazily-bridged NSStrings capable of providing access to contiguous ASCII/UTF-8 set the ObjC bit. Accessing shared string's pointer sh…

 to OC func _bridgeToObjectiveCImpl() -> AnyObject { if _guts.isSmall { return _guts.asSmall.withUTF8 { bufPtr in // TODO(String bridging): worth isASCII check for different encoding? return _swift_stdlib_CFStringCreateWithBytes( nil, bufPtr.baseAdd…