Re: [PR] [SPARK-46970][CORE] Rewrite `OpenHashSet#hasher` with `pattern matching` [spark]

["LuciferYang (via GitHub)" <gi...@apache.org>]

LuciferYang commented on code in PR #44998:
URL: https://github.com/apache/spark/pull/44998#discussion_r1477177975


##########
core/src/main/scala/org/apache/spark/util/collection/OpenHashSet.scala:
##########
@@ -62,28 +62,12 @@ class OpenHashSet[@specialized(Long, Int, Double, Float) T: ClassTag](
   // specialization to work (specialized class extends the non-specialized one and needs access
   // to the "private" variables).
 
-  protected val hasher: Hasher[T] = {
-    // It would've been more natural to write the following using pattern matching. But Scala 2.9.x
-    // compiler has a bug when specialization is used together with this pattern matching, and
-    // throws:
-    // scala.tools.nsc.symtab.Types$TypeError: type mismatch;
-    //  found   : scala.reflect.AnyValManifest[Long]
-    //  required: scala.reflect.ClassTag[Int]
-    //         at scala.tools.nsc.typechecker.Contexts$Context.error(Contexts.scala:298)
-    //         at scala.tools.nsc.typechecker.Infer$Inferencer.error(Infer.scala:207)
-    //         ...
-    val mt = classTag[T]
-    if (mt == ClassTag.Long) {
-      (new LongHasher).asInstanceOf[Hasher[T]]
-    } else if (mt == ClassTag.Int) {
-      (new IntHasher).asInstanceOf[Hasher[T]]
-    } else if (mt == ClassTag.Double) {
-      (new DoubleHasher).asInstanceOf[Hasher[T]]
-    } else if (mt == ClassTag.Float) {
-      (new FloatHasher).asInstanceOf[Hasher[T]]
-    } else {
-      new Hasher[T]
-    }
+  protected val hasher: Hasher[T] = classTag[T] match {
+    case ClassTag.Long => new LongHasher().asInstanceOf[Hasher[T]]
+    case ClassTag.Int => new IntHasher().asInstanceOf[Hasher[T]]
+    case ClassTag.Double => new DoubleHasher().asInstanceOf[Hasher[T]]
+    case ClassTag.Float => new FloatHasher().asInstanceOf[Hasher[T]]
+    case _ => new Hasher[T]

Review Comment:
   cc @cloud-fan @dongjoon-hyun @srowen 
   
   All test passed. Can we make this change?
   



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