Pattern match on inner trait cannot be checked at run time?
I tried pattern matching on an inner trait but it looks like this cannot be done. It also matches inner trait instances from other objects. It matches only inner (abstract) classes.
I cannot find why an inner trait cannot be checked at run time. Any suggestions?
With the code below I get this warning for 'def patternMatchA1': 'The outer reference in this type test cannot be checked at run time.'
trait A0
case class X() {
trait A1 extends A0
case class A() extends A1
def patternMatchA1(a: A0) = a match {
case a: A1 => true //The outer reference in this type test cannot be checked at run time.
case _ => false
}
def patternMatchA(a: A0) = a match {
case a: A => true
case _ => false
}
}
val Xa = X()
val Xb = X()
Xa.patternMatchA1(Xa.A()) //true
Xa.patternMatchA1(Xb.A()) //true -> I expected this to be false
Xa.patternMatchA(Xa.A()) //true
Xa.patternMatchA(Xb.A()) //false
scastie: https://scastie.scala-lang.org/gj2Tb6QaShiNNeRMMliwsQ
scala pattern-matching
asked Nov 20 '18 at 8:28
user3508638
7516
add a comment |
I tried pattern matching on an inner trait but it looks like this cannot be done. It also matches inner trait instances from other objects. It matches only inner (abstract) classes.
I cannot find why an inner trait cannot be checked at run time. Any suggestions?
With the code below I get this warning for 'def patternMatchA1': 'The outer reference in this type test cannot be checked at run time.'
trait A0
case class X() {
trait A1 extends A0
case class A() extends A1
def patternMatchA1(a: A0) = a match {
case a: A1 => true //The outer reference in this type test cannot be checked at run time.
case _ => false
}
def patternMatchA(a: A0) = a match {
case a: A => true
case _ => false
}
}
val Xa = X()
val Xb = X()
Xa.patternMatchA1(Xa.A()) //true
Xa.patternMatchA1(Xb.A()) //true -> I expected this to be false
Xa.patternMatchA(Xa.A()) //true
Xa.patternMatchA(Xb.A()) //false
scastie: https://scastie.scala-lang.org/gj2Tb6QaShiNNeRMMliwsQ
scala pattern-matching
asked Nov 20 '18 at 8:28
user3508638
7516
why it should be false? it is only false ifait's not anA1which clearly is
– RoberMP
Nov 20 '18 at 9:19
1
It should be false, just like the second case. This code is supposed to test path dependent types. But there is some limitation in the compiler.
– ygor
Nov 20 '18 at 9:29
1
Maybe related to issues.scala-lang.org/browse/SI-4440 ?
– ygor
Nov 20 '18 at 9:34
add a comment |
I tried pattern matching on an inner trait but it looks like this cannot be done. It also matches inner trait instances from other objects. It matches only inner (abstract) classes.
I cannot find why an inner trait cannot be checked at run time. Any suggestions?
With the code below I get this warning for 'def patternMatchA1': 'The outer reference in this type test cannot be checked at run time.'
trait A0
case class X() {
trait A1 extends A0
case class A() extends A1
def patternMatchA1(a: A0) = a match {
case a: A1 => true //The outer reference in this type test cannot be checked at run time.
case _ => false
}
def patternMatchA(a: A0) = a match {
case a: A => true
case _ => false
}
}
val Xa = X()
val Xb = X()
Xa.patternMatchA1(Xa.A()) //true
Xa.patternMatchA1(Xb.A()) //true -> I expected this to be false
Xa.patternMatchA(Xa.A()) //true
Xa.patternMatchA(Xb.A()) //false
scastie: https://scastie.scala-lang.org/gj2Tb6QaShiNNeRMMliwsQ
scala pattern-matching
asked Nov 20 '18 at 8:28
user3508638
7516
I tried pattern matching on an inner trait but it looks like this cannot be done. It also matches inner trait instances from other objects. It matches only inner (abstract) classes.
I cannot find why an inner trait cannot be checked at run time. Any suggestions?
With the code below I get this warning for 'def patternMatchA1': 'The outer reference in this type test cannot be checked at run time.'
trait A0
case class X() {
trait A1 extends A0
case class A() extends A1
def patternMatchA1(a: A0) = a match {
case a: A1 => true //The outer reference in this type test cannot be checked at run time.
case _ => false
}
def patternMatchA(a: A0) = a match {
case a: A => true
case _ => false
}
}
val Xa = X()
val Xb = X()
Xa.patternMatchA1(Xa.A()) //true
Xa.patternMatchA1(Xb.A()) //true -> I expected this to be false
Xa.patternMatchA(Xa.A()) //true
Xa.patternMatchA(Xb.A()) //false
scastie: https://scastie.scala-lang.org/gj2Tb6QaShiNNeRMMliwsQ
scala pattern-matching
scala pattern-matching
asked Nov 20 '18 at 8:28
user3508638
7516
asked Nov 20 '18 at 8:28
user3508638
7516
asked Nov 20 '18 at 8:28
user3508638
7516
asked Nov 20 '18 at 8:28
user3508638
7516
asked Nov 20 '18 at 8:28
user3508638
7516
7516
why it should be false? it is only false ifait's not anA1which clearly is
– RoberMP
Nov 20 '18 at 9:19
1
It should be false, just like the second case. This code is supposed to test path dependent types. But there is some limitation in the compiler.
– ygor
Nov 20 '18 at 9:29
1
Maybe related to issues.scala-lang.org/browse/SI-4440 ?
– ygor
Nov 20 '18 at 9:34
add a comment |
why it should be false? it is only false ifait's not anA1which clearly is
– RoberMP
Nov 20 '18 at 9:19
1
It should be false, just like the second case. This code is supposed to test path dependent types. But there is some limitation in the compiler.
– ygor
Nov 20 '18 at 9:29
1
Maybe related to issues.scala-lang.org/browse/SI-4440 ?
– ygor
Nov 20 '18 at 9:34
why it should be false? it is only false if
a it's not an A1 which clearly is– RoberMP
Nov 20 '18 at 9:19
why it should be false? it is only false if
a it's not an A1 which clearly is– RoberMP
Nov 20 '18 at 9:19
1
1
It should be false, just like the second case. This code is supposed to test path dependent types. But there is some limitation in the compiler.
– ygor
Nov 20 '18 at 9:29
It should be false, just like the second case. This code is supposed to test path dependent types. But there is some limitation in the compiler.
– ygor
Nov 20 '18 at 9:29
1
1
Maybe related to issues.scala-lang.org/browse/SI-4440 ?
– ygor
Nov 20 '18 at 9:34
Maybe related to issues.scala-lang.org/browse/SI-4440 ?
– ygor
Nov 20 '18 at 9:34
add a comment |
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why it should be false? it is only false if
ait's not anA1which clearly is– RoberMP
Nov 20 '18 at 9:19
1
It should be false, just like the second case. This code is supposed to test path dependent types. But there is some limitation in the compiler.
– ygor
Nov 20 '18 at 9:29
1
Maybe related to issues.scala-lang.org/browse/SI-4440 ?
– ygor
Nov 20 '18 at 9:34