Imported From: https://issues.scala-lang.org/browse/SI-9795?orig=1
Reporter: Fengyun Liu (liufengyun)
Affected Versions: 2.11.8

@som-snytt said:
Spec says constructor pattern must conform. I hope someone chimes in to say why. Maybe it made more sense when a case class could extend a case class. But current error for case class extension says, "To overcome this limitation, use extractors to pattern match on non-leaf nodes." Maybe the OP error message should give similar advice.

@SethTisue said:
I guess the spec language Andrew's referring to is SLS 8.1.6 (Constructor Patterns), "The pattern matches all objects created from constructor invocations c(...)..."

I don't know why, either.

@som-snytt said:
"it must conform to the expected type of the pattern", I believe. There could be subclasses C and D, so the idea is not to match (a: B) with C. Or maybe you want the selection x.v to mean something stable.

@SethTisue said:
ah, you're right, "it must conform to the expected type of the pattern" is the key phrase. (I had glossed over that in my reading, thinking the conformance went in the other direction.)

@som-snytt said:
That's because you're a non-conformist.

For fun,

scala> (new A("hi") { }) match { case A(s) => s }
<console>:14: error: constructor cannot be instantiated to expected type;
 found   : A(in object $iw)
 required: A(in object $iw)
       (new A("hi") { }) match { case A(s) => s }
                                      ^