FileIO.scala

import java.io._

object FileIO {
  abstract sealed class AccessMode
  case class READ() extends AccessMode
  case class WRITE() extends AccessMode
  case class READ_WRITE() extends AccessMode
  abstract sealed class StreamType
  case class BYTES() extends StreamType
  case class CHARS() extends StreamType

  trait FileOpener[M, T, R] {
    def open(path: File): R
  }

  implicit def pathNameToFile(pathName: String) = new File(pathName)

  object FileOpener {
    implicit object InputStreamOpener extends FileOpener[
      READ, BYTES, InputStream] {
        def open(path: File) = new FileInputStream(path)
      }
    implicit object OutputStreamOpener extends FileOpener[
      WRITE, BYTES, PrintStream] {
        def open(path: File) = new PrintStream(new FileOutputStream(path))
      }
    implicit object RandomAccessFileOpener extends FileOpener[
      READ_WRITE, BYTES, RandomAccessFile] {
        def open(path: File) = new RandomAccessFile(path, "rw")
      }
    implicit object ReaderOpener extends FileOpener[
      READ, CHARS, BufferedReader] {
        def open(path: File) = new BufferedReader(new FileReader(path))
      }
    implicit object WriterOpener extends FileOpener[
      WRITE, CHARS, PrintWriter] {
        def open(path: File) = new PrintWriter(new FileWriter(path))
      }
  }

  def open[M <: AccessMode, T <: StreamType, R](
    path: File, mode: M = READ(), streamType: T = CHARS()
  )(implicit opener: FileOpener[M, T, R]): R = opener.open(path)

  def using[R <: { def close(): Unit }, M](r: R)(f: R => M): M = try {
    f(r)
  } finally { r.close() }
}
import FileIO._
object User {
  def main(args: Array[String]) {
    using(open("Hello.scala")){reader =>
      //reader is BufferedReader
      Stream.continually(reader.readLine()).takeWhile(_ != null).foreach(println)
    }
    using(open("hoge.txt", WRITE())){writer =>
      //writer is PrintWriter
      writer.println("HogeHoge")
    }
  }
}