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From JoshRosen <...@git.apache.org>
Subject [GitHub] spark pull request #13504: [SPARK-15762][SQL] Cache Metadata & StructType ha...
Date Sat, 04 Jun 2016 21:13:22 GMT
Github user JoshRosen commented on a diff in the pull request:

    https://github.com/apache/spark/pull/13504#discussion_r65807740
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/types/Metadata.scala ---
    @@ -104,7 +104,8 @@ sealed class Metadata private[types] (private[types] val map: Map[String,
Any])
         }
       }
     
    -  override def hashCode: Int = Metadata.hash(this)
    +  private lazy val _hashCode: Int = Metadata.hash(this)
    +  override def hashCode: Int = _hashCode
    --- End diff --
    
    Making `hashCode` into a `lazy val` triggers compilation errors and triggers Scalastyle's
"You should implement equals and hashCode together" error; it also causes problems in Scala
code which calls `.hashCode()`:
    
    ```
    [error] /Users/joshrosen/Documents/spark/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala:247:
type mismatch;
    [error]  found   : AttributeReference.this.metadata.type (with underlying type org.apache.spark.sql.types.Metadata)
    [error]  required: ?{def hashCode(): ?}
    [error] Note that Metadata extends Any, not AnyRef.
    [error] Such types can participate in value classes, but instances
    [error] cannot appear in singleton types or in reference comparisons.
    [error]     h = h * 37 + metadata.hashCode()
    [error]                  ^
    [error] /Users/joshrosen/Documents/spark/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala:247:
Int does not take parameters
    [error]     h = h * 37 + metadata.hashCode()
    [error]                                   ^
    [error] two errors found
    [error] /Users/joshrosen/Documents/spark/sql/catalyst/src/main/scala/org/apache/spark/sql/types/Metadata.scala:41:13:
You should implement equals and hashCode together
    ```


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