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Fix type of the custom `ClassTag` in `PatternMatching.scala`

In fb31577 custom ClassTags were introduced to optimize array
creation in hot places. The idea was that if `Array[T]` is allocated
through `ClassTag[T]` (which is essentially a factory for Array[T])
we would introduce a custom class implementing `ClassTag[T]` interface
and would have specialized array allocation instruction instead of
having reflective call as it's being done with default (compiler
synthesized) implementation of `ClassTag[T]`.

In case of `PatternMatching.scala` I made a mistake of providing
`ClassTag[Array[Clause]]` instead of `ClassTag[Clause]` so that value
would never be used and compiler still would resolve implicit through
default mechanism. This has been discovered thanks to @paulp's work
on unused value detection.

Review by @paulp.
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1 parent 3b68b45 commit f98e4d05a68a8a41a92d292bd590ce765b1a6bd5 @gkossakowski gkossakowski committed Nov 9, 2012
Showing with 3 additions and 3 deletions.
  1. +3 −3 src/compiler/scala/tools/nsc/typechecker/PatternMatching.scala
@@ -2037,9 +2037,9 @@ trait PatternMatching extends Transform with TypingTransformers with ast.TreeDSL
// CNF: a formula is a conjunction of clauses
type Formula = Array[Clause]
/** Override Array creation for efficiency (to not go through reflection). */
- private implicit val formulaTag: scala.reflect.ClassTag[Formula] = new scala.reflect.ClassTag[Formula] {
- def runtimeClass: java.lang.Class[Formula] = classOf[Formula]
- final override def newArray(len: Int): Array[Formula] = new Array[Formula](len)
+ private implicit val clauseTag: scala.reflect.ClassTag[Clause] = new scala.reflect.ClassTag[Clause] {
+ def runtimeClass: java.lang.Class[Clause] = classOf[Clause]
+ final override def newArray(len: Int): Array[Clause] = new Array[Clause](len)
}
def formula(c: Clause*): Formula = c.toArray
def andFormula(a: Formula, b: Formula): Formula = a ++ b

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