[jira] [Comment Edited] (SPARK-2331) SparkContext.emptyRDD has wrong return type

["Ian Hummel (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-2331?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14048884#comment-14048884 ] 

Ian Hummel edited comment on SPARK-2331 at 7/1/14 1:46 PM:
-----------------------------------------------------------

Hi Sean,

The code I was testing was actually equivalent to your second example.  I'm not sure if this is a covariance issue or not though, because both the RDD and the EmptyRDD above are parameterized by type {{String}}.

Most of other RDD methods return {{RDD\[T\]}} explicitly.  Compare the functions below

{code}
  /** Build the union of a list of RDDs. */
  def union[T: ClassTag](rdds: Seq[RDD[T]]): RDD[T] = new UnionRDD(this, rdds)

  /** Build the union of a list of RDDs passed as variable-length arguments. */
  def union[T: ClassTag](first: RDD[T], rest: RDD[T]*): RDD[T] =
    new UnionRDD(this, Seq(first) ++ rest)

  /** Get an RDD that has no partitions or elements. */
  def emptyRDD[T: ClassTag] = new EmptyRDD[T](this)
{code}

Is it really just a case of forgetting to annotate the return type properly?


was (Author: themodernlife):
Hi Sean,

The code I was testing was actually equivalent to your second example.  I'm not sure if this is a covariance issue or not though, because both the RDD and the EmptyRDD above are parameterized by type {{String}}.

Most of other RDD methods return {{RDD[T]}} explicitly.  Compare the functions below

{monospace}
  /** Build the union of a list of RDDs. */
  def union[T: ClassTag](rdds: Seq[RDD[T]]): RDD[T] = new UnionRDD(this, rdds)

  /** Build the union of a list of RDDs passed as variable-length arguments. */
  def union[T: ClassTag](first: RDD[T], rest: RDD[T]*): RDD[T] =
    new UnionRDD(this, Seq(first) ++ rest)

  /** Get an RDD that has no partitions or elements. */
  def emptyRDD[T: ClassTag] = new EmptyRDD[T](this)
{monospace}

Is it really just a case of forgetting to annotate the return type properly?

> SparkContext.emptyRDD has wrong return type
> -------------------------------------------
>
>                 Key: SPARK-2331
>                 URL: https://issues.apache.org/jira/browse/SPARK-2331
>             Project: Spark
>          Issue Type: Bug
>    Affects Versions: 1.0.0
>            Reporter: Ian Hummel
>
> The return type for SparkContext.emptyRDD is EmptyRDD[T].
> It should be RDD[T].  That means you have to add extra type annotations on code like the below (which creates a union of RDDs over some subset of paths in a folder)
> val rdds = Seq("a", "b", "c").foldLeft[RDD[String]](sc.emptyRDD[String]) { (rdd, path) ⇒
>           rdd.union(sc.textFile(path))
>         }



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