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Pattern matching fails although a match exists #4124

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scabug opened this Issue Dec 31, 2010 · 4 comments

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scabug commented Dec 31, 2010

=== What steps will reproduce the problem (please be specific and use wikiformatting)? ===

scala> val body: AnyRef = <elem>hi</elem>
body: AnyRef = <elem>hi</elem>

scala> (body, "foo") match {
     |   case (node: Node, "bar") => "bye"
     |   case (ser: Serializable, "foo") => "hi"
     | }

=== What is the expected behavior? ===
print "hi"

=== What do you see instead? ===

scala.MatchError: (<elem>hi</elem>,foo)
        at .<init>(<console>:12)
        at .<clinit>(<console>)
        at RequestResult$$.<init>(<console>:9)
        at RequestResult$$.<clinit>(<console>)
        at RequestResult$$scala_repl_result(<console>)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at scala.tools.nsc.Interpreter$$Request$$$$anonfun$$loadAndRun$$1$$$$anonfun$$apply$$18.apply(Interpreter.scala:981)
        at scala.tools.nsc.Interpreter$$Request$$$$anonfun$$loadAndRun$$1$$$$anonfun$$apply$$18.apply(Interpreter.scala:981)
        at scala.util.control.Exception$$Catch.apply(Exception.scala:79)
        at scala...

=== Additional information ===
From @retronym:
scalac -Xprint:erasure is a more direct way to see how the pattern
match is translated.

<synthetic> val temp1: Tuple2 = new Tuple2(test.this.body(), "foo");
      if (temp1.ne(null))
        {
          <synthetic> val temp2: java.lang.Object = temp1._1();
          <synthetic> val temp3: java.lang.String =
temp1._2().$$asInstanceOf[java.lang.String]();
          if (temp2.$$isInstanceOf[scala.xml.Node]())
            {
              if (temp3.==("bar"))
                {
                  "bye"
                }
              else
                throw new MatchError(temp1)
            }
          else
            if (temp2.$$isInstanceOf[java.io.Serializable]())
              {
                if (temp3.==("foo"))
                  {
                    "hi"
                  }
                else
                  throw new MatchError(temp1)
              }
            else
              throw new MatchError(temp1)
        }
      else
        throw new MatchError(temp1)
    }

Seems like a close cousin of #2337 and #1697 r1r2. You can read some
commentary from Paul r3, from the build up to Scala 2.8.

=== What versions of the following are you using? ===

  • Scala:2.8.1
  • Java:1.6
  • Operating system: windows 7 64
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scabug commented Dec 31, 2010

Imported From: https://issues.scala-lang.org/browse/SI-4124?orig=1
Reporter: Ittay Dror (ittayd)

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scabug commented Jan 4, 2011

@hubertp said:
Looks like your department, Paul.

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scabug commented May 12, 2012

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scabug commented May 12, 2012

@retronym said:
Test case pending merge, works in master.

@scabug scabug closed this May 12, 2012

@scabug scabug added the patmat label Apr 7, 2017

@scabug scabug added this to the 2.10.0-M3 milestone Apr 7, 2017

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