“r0”,“r1”等在Scala中有特殊意义吗？

代码：

package qndTests2

sealed abstract case class Reg()
trait RReg
trait RRegNotPc extends RReg
trait LowReg extends RReg
sealed abstract case class LowRegClass() extends Reg with LowReg
sealed abstract case class RRegNotPcClass() extends Reg with RRegNotPc
case object R0 extends LowRegClass
case object R1 extends LowRegClass
case object R2 extends RRegNotPcClass
case object R3 extends Reg with RReg

sealed abstract case class Base()
trait T1
trait T2 extends T1
trait T3 extends T1
sealed abstract case class CaseClassT3() extends Base with T3
sealed abstract case class CaseClassT2() extends Base with T2
case object r0 extends CaseClassT3
case object r1 extends CaseClassT3
case object r2 extends CaseClassT2
case object r3 extends Base with T1

object test {
  def regToInt(r: RReg): Int = {
    r match{
      case R0 => 0
      case R1 => 1
      case R2 => 2
      case R3 => 3
    }
  }
  def toInt(r: T1): Int = {
    r match{
      case r0 => 0
      case r1 => 1   //error: unreachable code
      case r2 => 2   //error: unreachable code
      case r3 => 3   //error: unreachable code
    }
  }
  def main(args: Array[String]): Unit = {
    println(toInt(r0))
    println(toInt(r1))
    println(regToInt(R0))
    println(regToInt(R3))
  }
}

包“qndTests2”只包含一个文件Test.scala,文件的完整内容在上面.
将“r0”?“r3”替换为“A”?“D”,然后编译！
我不是为什么……
我只是很累,忽略了一些明显的东西???