Swift里字符串（六）Shared strings

最新推荐文章于 2024-12-20 12:11:49 发布

转载最新推荐文章于 2024-12-20 12:11:49 发布 · 293 阅读

0 ·

CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/huahuahu/p/Swift-li-zi-fu-chuan-liuShared-strings.html

文章标签：

#swift

博客介绍了Swift中共享字符串的特性，其无尾部分配存储但可访问连续UTF - 8代码单元，懒桥接的NSStrings能访问连续ASCII/UTF - 8并设置ObjC位。还提及字符串数据不从内部起始，同时阐述了在OC runtime下的子类化情况及内存布局。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

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 should always be behind a resilience barrier, permitting future evolution.

字符串数据没有从内部_object处起始，但是可以获取连续的 utf-8 code unit。
对应的类是__SharedStringStorage。

内存布局

在 OC runtime下，是 `NSString` 子类

子类化 `NSString`

#if _runtime(_ObjC)

  @objc(length)
  final internal var length: Int {
    @_effects(readonly) get {
      return asString.utf16.count // UTF16View special-cases ASCII for us.
    }
  }

  @objc(characterAtIndex:)
  @_effects(readonly)
  final internal func character(at offset: Int) -> UInt16 {
    let str = asString
    return str.utf16[str._toUTF16Index(offset)]
  }

  @objc(getCharacters:range:)
  @_effects(releasenone)
  final internal func getCharacters(
    _ buffer: UnsafeMutablePointer<UInt16>, range aRange: _SwiftNSRange
  ) {
    _getCharacters(buffer, aRange)
  }

转载于:https://www.cnblogs.com/huahuahu/p/Swift-li-zi-fu-chuan-liuShared-strings.html