func print<Target>(_ items: Any...,separator: String = default,terminator: String = default,to output: inout Target) where Target : TextOutputStream

和

func debugPrint<Target>(_ items: Any...,to output: inout Target) where Target : TextOutputStream

您可以创建一个实现TextOutputStream的对象,该对象将消息保存到您选择的文件中.如果您已在代码库中已有现有打印件,则此功能非常有用.然后,您只需将附加参数添加到它们即可.请记住,这些打印将停止记录到标准输出(控制台).

Documentation for print

Documentation for debugPrint

例：

final class LogDestination: TextOutputStream {
  private let path: String
  init() {
    let paths = NSSearchPathForDirectoriesInDomains(.documentDirectory,.userDomainMask,true)
    path = paths.first! + "/log"
  }

  func write(_ string: String) {
    if let data = string.data(using: .utf8),let fileHandle = FileHandle(forWritingAtPath: path) {
      defer {
        fileHandle.closeFile()
      }
      fileHandle.seekToEndOfFile()
      fileHandle.write(data)
    }
  }
}

然后

// I would probably use Singleton for this
var dest = LogDestination()
print("My test message",to: &dest)