After reading this excellent question/answer on type erasure in Scala, I tried this code. The Scala compiler did not output a type erasure warning.
scala> val x: List[Int] = List(1,2,3)
x: List[Int] = List(1, 2, 3)
scala> x match {
| case List(x: Int) => println("a")
| case _ => println("false")
| }
false
Why doesn't the above code output the same warning as this code:
scala> List(1,2,3) match {
| case l: List[String] => println("list of strings")
| case _ => println("ok")
| }
<console>:9: warning: fruitless type test: a value of type List[Int] cannot
also be a List[String] (but still might match its erasure)
case l: List[String] => println("list of strings")
^
list of strings
The first case is not just testing type - it's testing by pattern-match that the list has exactly one integer element.
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