memo.scala

 def saveAsTextFile(path: String): Unit = withScope {
    // https://issues.apache.org/jira/browse/SPARK-2075
    //
    // NullWritable is a `Comparable` in Hadoop 1.+, so the compiler cannot find an implicit
    // Ordering for it and will use the default `null`. However, it's a `Comparable[NullWritable]`
    // in Hadoop 2.+, so the compiler will call the implicit `Ordering.ordered` method to create an
    // Ordering for `NullWritable`. That's why the compiler will generate different anonymous
    // classes for `saveAsTextFile` in Hadoop 1.+ and Hadoop 2.+.
    //
    // Therefore, here we provide an explicit Ordering `null` to make sure the compiler generate
    // same bytecodes for `saveAsTextFile`.
    val nullWritableClassTag = implicitly[ClassTag[NullWritable]]
    val textClassTag = implicitly[ClassTag[Text]]
    val r = this.mapPartitions { iter =>
      val text = new Text()
      iter.map { x =>
        text.set(x.toString)
        (NullWritable.get(), text)
      }
    }
    RDD.rddToPairRDDFunctions(r)(nullWritableClassTag, textClassTag, null)
      .saveAsHadoopFile[TextOutputFormat[NullWritable, Text]](path)
  }