Allow multiple wildcard vals

[odersky]

Allow multiple definitions of the form

val _: T = e

in a scope. Translate them by changing the _ to fresh
wildcardParamNames.

[som-snytt]

I see Scala 2

class C { val _ = 42 ; val _: Int = 27 ; val _: String = Array(17) }

is

          <synthetic> <artifact> private[this] val x$1 = 42: @scala.unchecked match {
            case _ => ()
          };
          <synthetic> <artifact> private[this] val x$2 = 27: @scala.unchecked match {
            case (_: Int) => ()
          };
          <synthetic> <artifact> private[this] val x$3 = Array(17): @scala.unchecked match {
            case (_: String) => ()
          }

so

       error: scrutinee is incompatible with pattern type;
        found   : String
        required: Array[Int]

instead of

       error: type mismatch;
        found   : Array[Int]
        required: String

I don't know what the expectation was, but I would expect val _ = Array() to keep a reference to my allocation. I can't tell if that is a bug or feature without a coin, and who carries coins any more?

[odersky]

@som-snytt I'd say the Scala 3 error message is preferable.

[julienrf]

That looks good to me.

[som-snytt]

BTW, after trying it out, I see the Scala 2 behavior is the same except for that one error message.

My point was actually that I would expect

val _ = new Thing

to keep my Thing from getting garbage-collected. But I guess that qualifies as neither a feature nor a bug.