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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