在Swift 3(libxml2)中将String转换为UnsafePointer <xmlChar>的更快捷的方法

Question

我正在为libxml2 C库开发一个Swift 3包装器.

转换String为两种便捷方法,UnsafePointer<xmlChar>反之亦然.在libxml2 xmlChar中声明为unsigned char.

• UnsafePointer<xmlChar>到String是简单

  func stringFrom(xmlchar: UnsafePointer<xmlChar>) -> String {
      let string = xmlchar.withMemoryRebound(to: CChar.self, capacity: 1) {
          return String(validatingUTF8: $0)
      }
      return string ?? ""
  }
  

• 对于String到UnsafePointer<xmlChar>我试过,例如很多事情

  let bytes = string.utf8CString.map{ xmlChar($0) }
  return UnsafePointer<xmlChar>(bytes)
  

  但这不起作用,我发现的唯一可行解决方案是

  func xmlCharFrom(string: String) -> UnsafePointer<xmlChar> {
      let pointer = (string as NSString).utf8String
      return unsafeBitCast(pointer, to: UnsafePointer<xmlChar>.self)
  }
  

有没有更好的,swiftier没有桥投地的方式NSString和unsafeBitCast？

Answer 1

我能想到的最快的方法就是使用bitPattern:初始化程序:

let xmlstr = str.utf8CString.map { xmlChar(bitPattern: $0) }

这会给你一个Array的xmlChar秒.坚持下去,当你需要传递给某个东西时使用Array's withUnsafeBufferPointer方法UnsafePointer:

xmlstr.withUnsafeBufferPointer { someAPIThatWantsAPointer($0.baseAddress!) }

不要让UnsafePointer关闭逃脱,因为它在外面是无效的.

编辑:如何妥协？不要让你的函数返回一个指针,而是让它关闭.

func withXmlString<T>(from string: String, handler: (UnsafePointer<xmlChar>) throws -> T) rethrows -> T {
    let xmlstr = string.utf8CString.map { xmlChar(bitPattern: $0) }

    return try xmlstr.withUnsafeBufferPointer { try handler($0.baseAddress!) }
}

或者,作为扩展String:

extension String {
    func withXmlString<T>(handler: (UnsafePointer<xmlChar>) throws -> T) rethrows -> T {
        let xmlstr = self.utf8CString.map { xmlChar(bitPattern: $0) }

        return try xmlstr.withUnsafeBufferPointer { try handler($0.baseAddress!) }
    }
}