Avoid redundant expensive string computation in Definitions.FunType

Author: odersky

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1412,8 +1412,8 @@ class Definitions {
         val classRefs1 = new Array[TypeRef | Null](classRefs.length * 2)
         Array.copy(classRefs, 0, classRefs1, 0, classRefs.length)
         classRefs = classRefs1
-      val funName = s"scala.$prefix$n"
       if classRefs(n) == null then
+        val funName = s"scala.$prefix$n"
         classRefs(n) =
           if prefix.startsWith("Impure")
           then staticRef(funName.toTypeName).symbol.typeRef