Int convert to Double when unnecessary

[scabug]

The second result type should be Int

def f1(l: Array[Int]): Array[Any] =
      l.map{ x =>
        x match {
        case x if x == 1 => x.toString
        case x if x == 2 => x.toInt
        case _ => x.toDouble
      }    
   } 

f1(Array(1,2,3)).foreach(v => println(s"$v :${v.getClass}"))
1 :class java.lang.String
2.0 :class java.lang.Double
3.0 :class java.lang.Double

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-9935?orig=1
Reporter: Xuefeng Wu (wuxuefeng)
Affected Versions: 2.11.8, 2.12.0-RC1

[scabug]

@SethTisue said:
Note that the following behavior is correct:

scala> Array(true, false) map { case true => 1; case false => 2.0 }
res7: Array[Double] = Array(1.0, 2.0)

because of the weak-least-upper-bound rule in SLS 8.4.

Regardless, the behavior in your example does seem incorrect to me. Looks like a bug in weak-least-upper-bound handling in the pattern matcher. The weak-least-upper-bound of Int, Double, and String is Any; I don't see anything in the spec that would permit the weak-least-upper-bound of only a subset of the clauses to influence the results.

Note that the behavior is sensitive to the ordering of clauses in the match, so for example you get different results if String comes last:

  l.map{
    case x if x == 1 => x.toInt
    case x if x == 2 => x.toDouble
    case x => x.toString
  }

1 :class java.lang.Integer
2.0 :class java.lang.Double
3 :class java.lang.String

[scabug]

@SethTisue said:
Dotty doesn't have the bug.

[SethTisue]

Dotty doesn't have the bug

(because Scala 3 doesn't have weak conformance at all)

[som-snytt]

I tried variants but could not reproduce on 2.13.

scala> def f(xs: Array[Int]) = xs.map(x => x match {
     | case x if x == 1 => x.toString
     | case x if x == 2 => x.toInt
     | case _ => x.toDouble
     | })
def f(xs: Array[Int]): Array[Any]

scala> f(Array(1,2,3))
val res6: Array[Any] = Array(1, 2, 3.0)

Reproduces on 2.11.12 but not 2.12.20.

scala> Array(1,2,3).map { case x@1 => x.toString case x@2 => x.toInt case x@3 => x.toDouble }
val res2: Array[Any] = Array(1, 2, 3.0)

oh actually

Welcome to Scala 2.11.12 (OpenJDK 64-Bit Server VM, Java 1.8.0_352).
Type in expressions for evaluation. Or try :help.

scala> Array(1,2,3).map { case x@1 => x.toString case x@2 => x.toInt case x@3 => x.toDouble }
res0: Array[Any] = Array(1, 2, 3.0)

scala> Array(1,2,3).map { case x if x == 1 => x.toString case x if x == 2 => x.toInt case x if x == 3 => x.toDouble }
res1: Array[Any] = Array(1, 2.0, 3.0)