The various
examples generally have the form
def identifier = """[_\p{L}][_\p{L}\p{Nd}]*""".r
This works fine, but the underlying Java Pattern is recompiled on every reference.
The behavior came to light during an upgrade from Java 6 and Scala 2.7.7 to Java 7 and Scala 2.9.2, when a ~ 10% performance degradation was noted.
Performance analysis indicated an unexpected large number of calls to
Pattern.compile.
The Java 7 implementation is evidently somewhat slower.
Changing the def to val resolves the problem, without impact to the semantics.
In this case, the improvement was greater than 30% which more than compensates for the degradation.