scala/scala — pull request #1091 by paulp (2012-08-08 16:45:06+00:00)
Title: Better pattern matcher error message.

For the common case when someone hasn't quite grokked
the significance of lower case in a pattern match. I'd
like to make all the unreachables errors, not warnings,
but there may be a bug or two to clear out first.

class A {
def badEquals(x: Any, y: Any) = x match {
case y => true
case _ => false
}
}

a.scala:3: warning: patterns after a variable pattern cannot match (SLS 8.1.1)
If you intended to match against parameter y of method badEquals, you must use backticks, like: case `y` =>
case y => true
^
a.scala:4: warning: unreachable code due to variable pattern 'y' on line 3
case _ => false
^
two warnings found