class A extends Product2[Int, String] {
  def _1: Int = 1
  def _2: String = "1"
  def isEmpty: Boolean = false
  def get: A = this
  def canEqual(that: Any) = true
}
 
object A {
  def unapply(a: A) = a
}

(new A) match {case A(1, "1") => true; case _ => false}

class A {
  def isEmpty: Boolean = false
  def get: Int = 1
}
 
object A {
  def unapply(a: A) = a
}

(new A) match {case A(1) => true; case _ => false}

type If
implicit val IfTag: ClassTag[If]
trait DeconstructorCommon[T >: Null <: Tree] {
    var field: T = null
    def get: this.type = this
    def isEmpty: Boolean = field eq null
    def isDefined = !isEmpty
    def unapply(s: T): this.type ={
      field = s
      this
    }
  }
trait IfDeconstructor extends DeconstructorCommon[If]{
    def _1: Tree
    def _2: Tree
    def _3: Tree
  }

            Tuple3 tuple3;
            Object object = tree;
            Option option = this.scala$tools$nsc$backend$jvm$BCodeBodyBuilder$PlainBodyBuilder$$$outer().int().IfTag().unapply(object);
            if (option.isEmpty()) throw new MatchError(object);
            Object object2 = option.get();
            BackendInterface.IfDeconstructor ifDeconstructor = (BackendInterface.IfDeconstructor)this.scala$tools$nsc$backend$jvm$BCodeBodyBuilder$PlainBodyBuilder$$$outer().int().If().unapply(object2);
            if (ifDeconstructor.isEmpty()) {
                throw new MatchError(object);
            }
            Object condp = ((BackendInterface.IfDeconstructor)ifDeconstructor.get())._1();
            Object thenp = ((BackendInterface.IfDeconstructor)ifDeconstructor.get())._2();
            Object elsep = ((BackendInterface.IfDeconstructor)ifDeconstructor.get())._3();
            Tuple3 tuple32 = tuple3 = new Tuple3(condp, thenp, elsep);
            Object condp2 = tuple32._1();
            Object thenp2 = tuple32._2();
            Object elsep2 = tuple32._3();

 cat sandbox/client.scala
trait Client extends Test {
  def test() {
    val If(condp, thenp, elsep) = (??? : Tree)
  }
}
2.11.x /code/scala2 qscalac sandbox/test.scala && qscalac -Xprint:parser sandbox/client.scala
[[syntax trees at end of                    parser]] // client.scala
package <empty> {
  abstract trait Client extends Test {
    def $init$() = {
      ()
    };
    def test(): scala.Unit = {
      <synthetic> <artifact> private[this] val x$1 = ($qmark$qmark$qmark: Tree): @scala.unchecked match {
        case If((condp @ _), (thenp @ _), (elsep @ _)) => scala.Tuple3(condp, thenp, elsep)
      };
      val condp = x$1._1;
      val thenp = x$1._2;
      val elsep = x$1._3;
      ()
    }
  }
}

  var x$1: ? = _
  var x$2: ? = _
  var x$3: ? = _
  scrut match {
    case Pattern(a, b, c) =>
      x$1 = a
      x$2 = b
      x$3 = c
    case => throw ...
  }
  val condp = x$1
  val elsep = x$2
  val thenp = x$3