Why is there a difference in behavior between these two pattern matches in a for comprehension?

Question

Consider this Map[String, Any]:

val m1 = Map((\"k1\" -> \"v1\"), (\"k2\" -> 10))

Now let\'s write a for:

Answer 1

Well, the latter example doesn't work because it isn't spec'ed to. There's some discussion as to what would be the reasonable behavior. Personally, I'd expect it to work just like you. The thing is that:

val v: String = (10: Any) // is a compile error
(10: Any) match {
    case v: String =>
} // throws an exception

If you are not convinced by this, join the club. :-) Here's a workaround:

for (va @ (v: String) <- l1) println(v)

Note that in Scala 3, you can:

for (case v: String <- l1) println(v)