Pattern matching reified types in 2.8

Not automatically, no.
You can, of course, hack your own:
  case class OhPlease[T](x: T)(implicit val m: Manifest[T])
  def matchIt(in: OhPlease[_]): String = in.m.toString match {     case str if str == manifest[String].toString => in.x.asInstanceOf[String]    case int if int == manifest[Int].toString => (in.x.asInstanceOf[Int] * 5).toString    case _ => "None"   }
--j
On Mon, Mar 1, 2010 at 4:50 PM, David Pollak <feeder.of.the.bears@gmail.com> wrote:

Folks,

If there's a reified generic, does pattern matching take that into account in 2.8?

For example:

case class OhPlease[T: Manifest](x: T)

def matchIt(in: OhPlease[_]): String = in match {
  case n: OhPlease[String] = n.x
  case v: OhPlease[Int] = (v.x * 5).toString
  case _ => "None"
}

Will this work around the type erasure thingy?

Thanks,

David

On Mon, Mar 1, 2010 at 4:57 PM, Jorge Ortiz <jorge.ortiz@gmail.com> wrote:

Not automatically, no.
You can, of course, hack your own:
  case class OhPlease[T](x: T)(implicit val m: Manifest[T])
  def matchIt(in: OhPlease[_]): String = in.m.toString match {     case str if str == manifest[String].toString => in.x.asInstanceOf[String]

Actually, this won't work because the equals operator on manifests is broken.  Plus, you'd want to do the is instance of thing (is that transitive with manifests)...

Okay... I guess that part of Beginning Scala 2nd edition doesn't get written. :-(
 

    case int if int == manifest[Int].toString => (in.x.asInstanceOf[Int] * 5).toString    case _ => "None"   }
--j
On Mon, Mar 1, 2010 at 4:50 PM, David Pollak <feeder.of.the.bears@gmail.com> wrote:

Folks,

If there's a reified generic, does pattern matching take that into account in 2.8?

For example:

case class OhPlease[T: Manifest](x: T)

def matchIt(in: OhPlease[_]): String = in match {
  case n: OhPlease[String] = n.x
  case v: OhPlease[Int] = (v.x * 5).toString
  case _ => "None"
}

Will this work around the type erasure thingy?

Thanks,

David

While equality is broken, others methods aren't. Consider the example at http://stackoverflow.com/questions/1094173/how-do-i-get-around-type-erasure-on-scala-or-why-cant-i-get-the-type-parameter/1094214#1094214, for instance.

On Mon, Mar 1, 2010 at 10:07 PM, David Pollak <feeder.of.the.bears@gmail.com> wrote:

On Mon, Mar 1, 2010 at 4:57 PM, Jorge Ortiz <jorge.ortiz@gmail.com> wrote:

Not automatically, no.
You can, of course, hack your own:
  case class OhPlease[T](x: T)(implicit val m: Manifest[T])
  def matchIt(in: OhPlease[_]): String = in.m.toString match {     case str if str == manifest[String].toString => in.x.asInstanceOf[String]

Actually, this won't work because the equals operator on manifests is broken.  Plus, you'd want to do the is instance of thing (is that transitive with manifests)...

Okay... I guess that part of Beginning Scala 2nd edition doesn't get written. :-(
 

    case int if int == manifest[Int].toString => (in.x.asInstanceOf[Int] * 5).toString    case _ => "None"   }
--j
On Mon, Mar 1, 2010 at 4:50 PM, David Pollak <feeder.of.the.bears@gmail.com> wrote:

Folks,

If there's a reified generic, does pattern matching take that into account in 2.8?

For example:

case class OhPlease[T: Manifest](x: T)

def matchIt(in: OhPlease[_]): String = in match {
  case n: OhPlease[String] = n.x
  case v: OhPlease[Int] = (v.x * 5).toString
  case _ => "None"
}

Will this work around the type erasure thingy?

Thanks,

David

Further besides, that equals method in that example belongs to String, not Manifest. :-)

On Mon, Mar 1, 2010 at 10:07 PM, David Pollak <feeder.of.the.bears@gmail.com> wrote:

On Mon, Mar 1, 2010 at 4:57 PM, Jorge Ortiz <jorge.ortiz@gmail.com> wrote:

Not automatically, no.
You can, of course, hack your own:
  case class OhPlease[T](x: T)(implicit val m: Manifest[T])
  def matchIt(in: OhPlease[_]): String = in.m.toString match {     case str if str == manifest[String].toString => in.x.asInstanceOf[String]

Actually, this won't work because the equals operator on manifests is broken.  Plus, you'd want to do the is instance of thing (is that transitive with manifests)...

Okay... I guess that part of Beginning Scala 2nd edition doesn't get written. :-(
 

    case int if int == manifest[Int].toString => (in.x.asInstanceOf[Int] * 5).toString    case _ => "None"   }
--j
On Mon, Mar 1, 2010 at 4:50 PM, David Pollak <feeder.of.the.bears@gmail.com> wrote:

Folks,

If there's a reified generic, does pattern matching take that into account in 2.8?

For example:

case class OhPlease[T: Manifest](x: T)

def matchIt(in: OhPlease[_]): String = in match {
  case n: OhPlease[String] = n.x
  case v: OhPlease[Int] = (v.x * 5).toString
  case _ => "None"
}

Will this work around the type erasure thingy?

Thanks,

David

On Mon, Mar 01, 2010 at 04:50:35PM -0800, David Pollak wrote:
> If there's a reified generic, does pattern matching take that into
> account in 2.8?
>
> For example:
>
> case class OhPlease[T: Manifest](x: T)

I obtained agreement-in-principle to do this when martin was here,
matter of details and priorities.

On Mon, Mar 01, 2010 at 05:07:27PM -0800, David Pollak wrote:
> Actually, this won't work because the equals operator on manifests is
> broken.

Are you sure? What do you mean by equals exactly, what do you expect to
happen? You better open a ticket if you know something. When I write a
test case this long it's kind of in somebody else's court to tell me if
there are issues. I checked this in Dec 9 along with all the code which
made it pass.

object Test
{
object Variances extends Enumeration {
val CO, IN, CONTRA = Value
}
import Variances.{ CO, IN, CONTRA }

object SubtypeRelationship extends Enumeration {
val NONE, SAME, SUB, SUPER = Value
}
import SubtypeRelationship.{ NONE, SAME, SUB, SUPER }

class VarianceTester[T, U, CC[_]](expected: Variances.Value)(
implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) {

def elements = List(ev1 <:< ev2, ev2 <:< ev1)
def containers = List(ev3 <:< ev4, ev4 <:< ev3)

def isUnrelated = typeCompare[T, U] == NONE
def isSame = typeCompare[T, U] == SAME
def isSub = typeCompare[T, U] == SUB
def isSuper = typeCompare[T, U] == SUPER

def showsCovariance = (elements == containers)
def showsContravariance = (elements == containers.reverse)
def showsInvariance = containers forall (_ == isSame)

def allContainerVariances = List(showsCovariance, showsInvariance, showsContravariance)

def showsExpectedVariance =
if (isUnrelated) allContainerVariances forall (_ == false)
else if (isSame) allContainerVariances forall (_ == true)
else expected match {
case CO => showsCovariance && !showsContravariance && !showsInvariance
case IN => showsInvariance && !showsCovariance && !showsContravariance
case CONTRA => showsContravariance && !showsCovariance && !showsInvariance
}
}

def showsCovariance[T, U, CC[_]](implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) =
new VarianceTester[T, U, CC](CO) showsExpectedVariance

def showsInvariance[T, U, CC[_]](implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) =
new VarianceTester[T, U, CC](IN) showsExpectedVariance

def showsContravariance[T, U, CC[_]](implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) =
new VarianceTester[T, U, CC](CONTRA) showsExpectedVariance

def typeCompare[T, U](implicit ev1: Manifest[T], ev2: Manifest[U]) = (ev1 <:< ev2, ev2 <:< ev1) match {
case (true, true) => SAME
case (true, false) => SUB
case (false, true) => SUPER
case (false, false) => NONE
}

def assertAnyRef[T: Manifest] = List(
manifest[T] <:< manifest[Any],
manifest[T] <:< manifest[AnyRef],
!(manifest[T] <:< manifest[AnyVal])
) foreach (assert(_, "assertAnyRef"))

def assertAnyVal[T: Manifest] = List(
manifest[T] <:< manifest[Any],
!(manifest[T] <:< manifest[AnyRef]),
manifest[T] <:< manifest[AnyVal]
) foreach (assert(_, "assertAnyVal"))

def assertSameType[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == SAME, "assertSameType")
def assertSuperType[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == SUPER, "assertSuperType")
def assertSubType[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == SUB, "assertSubType")
def assertNoRelationship[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == NONE, "assertNoRelationship")

def testVariancesVia[T: Manifest, U: Manifest] = assert(
typeCompare[T, U] == SUB &&
showsCovariance[T, U, List] &&
showsInvariance[T, U, Set],
"testVariancesVia"
)

def runAllTests = {
assertAnyVal[AnyVal]
assertAnyVal[Unit]
assertAnyVal[Int]
assertAnyVal[Double]
assertAnyVal[Boolean]
assertAnyVal[Char]

assertAnyRef[AnyRef]
assertAnyRef[java.lang.Object]
assertAnyRef[java.lang.Integer]
assertAnyRef[java.lang.Double]
assertAnyRef[java.lang.Boolean]
assertAnyRef[java.lang.Character]
assertAnyRef[String]
assertAnyRef[scala.List[String]]
assertAnyRef[scala.List[_]]

// variance doesn't work yet
// testVariancesVia[String, Any]
// testVariancesVia[String, AnyRef]

assertSubType[List[String], List[Any]]
assertSubType[List[String], List[AnyRef]]
assertNoRelationship[List[String], List[AnyVal]]

assertSubType[List[Int], List[Any]]
assertSubType[List[Int], List[AnyVal]]
assertNoRelationship[List[Int], List[AnyRef]]

// Nothing
assertSubType[Nothing, Any]
assertSubType[Nothing, AnyVal]
assertSubType[Nothing, AnyRef]
assertSubType[Nothing, String]
assertSubType[Nothing, List[String]]
assertSubType[Nothing, Null]
assertSameType[Nothing, Nothing]

// Null
assertSubType[Null, Any]
assertNoRelationship[Null, AnyVal]
assertSubType[Null, AnyRef]
assertSubType[Null, String]
assertSubType[Null, List[String]]
assertSameType[Null, Null]
assertSuperType[Null, Nothing]

// Any
assertSameType[Any, Any]
assertSuperType[Any, AnyVal]
assertSuperType[Any, AnyRef]
assertSuperType[Any, String]
assertSuperType[Any, List[String]]
assertSuperType[Any, Null]
assertSuperType[Any, Nothing]

// Misc unrelated types
assertNoRelationship[Unit, AnyRef]
assertNoRelationship[Unit, Int]
assertNoRelationship[Int, Long]
assertNoRelationship[Boolean, String]
assertNoRelationship[List[Boolean], List[String]]
assertNoRelationship[Set[Boolean], Set[String]]
}

def main(args: Array[String]): Unit = runAllTests
}

On Mon, Mar 1, 2010 at 8:46 PM, Paul Phillips <paulp@improving.org> wrote:

On Mon, Mar 01, 2010 at 04:50:35PM -0800, David Pollak wrote:
> If there's a reified generic, does pattern matching take that into
> account in 2.8?
>
> For example:
>
> case class OhPlease[T: Manifest](x: T)

I obtained agreement-in-principle to do this when martin was here,
matter of details and priorities.

Very cool.
 

On Mon, Mar 01, 2010 at 05:07:27PM -0800, David Pollak wrote:
> Actually, this won't work because the equals operator on manifests is
> broken.

Are you sure? What do you mean by equals exactly, what do you expect to
happen? You better open a ticket if you know something.  When I write a
test case this long it's kind of in somebody else's court to tell me if
there are issues.  I checked this in Dec 9 along with all the code which
made it pass.

First, the hashCodes are never the same between Manifests of the same class:

dpp@yak:~$ scala
Welcome to Scala version 2.8.0.Beta1-prerelease (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_15).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val m1 = manifest[String]
m1: Manifest[String] = java.lang.String

scala> val m2 = manifest[String]
m2: Manifest[String] = java.lang.String

scala> m1.hashCode == m2.hashCode
res0: Boolean = false


Second, equality testing seems to be on the class itself, not the whole Manifest (although equality testing on manifest.toString) does do the right thing:

scala> val m3 = manifest[List[Int]]
m3: Manifest[List[Int]] = scala.collection.immutable.List[Int]

scala> val m4 = manifest[List[String]]
m4: Manifest[List[String]] = scala.collection.immutable.List[java.lang.String]

scala> m3 == m4
res1: Boolean = true

scala>

I'm okay if this stuff is way hard, difficult to build proofs for and outside the scope of 2.8.

Thanks,

David

 

object Test
{
 object Variances extends Enumeration {
   val CO, IN, CONTRA = Value
 }
 import Variances.{ CO, IN, CONTRA }

 object SubtypeRelationship extends Enumeration {
   val NONE, SAME, SUB, SUPER = Value
 }
 import SubtypeRelationship.{ NONE, SAME, SUB, SUPER }

 class VarianceTester[T, U, CC[_]](expected: Variances.Value)(
           implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) {

   def elements = List(ev1 <:< ev2, ev2 <:< ev1)
   def containers = List(ev3 <:< ev4, ev4 <:< ev3)

   def isUnrelated = typeCompare[T, U] == NONE
   def isSame = typeCompare[T, U] == SAME
   def isSub = typeCompare[T, U] == SUB
   def isSuper = typeCompare[T, U] == SUPER

   def showsCovariance = (elements == containers)
   def showsContravariance = (elements == containers.reverse)
   def showsInvariance = containers forall (_ == isSame)

   def allContainerVariances = List(showsCovariance, showsInvariance, showsContravariance)

   def showsExpectedVariance =
     if (isUnrelated) allContainerVariances forall (_ == false)
     else if (isSame) allContainerVariances forall (_ == true)
     else expected match {
       case CO     => showsCovariance && !showsContravariance && !showsInvariance
       case IN     => showsInvariance && !showsCovariance && !showsContravariance
       case CONTRA => showsContravariance && !showsCovariance && !showsInvariance
     }
 }

 def showsCovariance[T, U, CC[_]](implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) =
   new VarianceTester[T, U, CC](CO) showsExpectedVariance

 def showsInvariance[T, U, CC[_]](implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) =
   new VarianceTester[T, U, CC](IN) showsExpectedVariance

 def showsContravariance[T, U, CC[_]](implicit ev1: Manifest[T], ev2: Manifest[U], ev3: Manifest[CC[T]], ev4: Manifest[CC[U]]) =
   new VarianceTester[T, U, CC](CONTRA) showsExpectedVariance

 def typeCompare[T, U](implicit ev1: Manifest[T], ev2: Manifest[U]) = (ev1 <:< ev2, ev2 <:< ev1) match {
   case (true, true)   => SAME
   case (true, false)  => SUB
   case (false, true)  => SUPER
   case (false, false) => NONE
 }

 def assertAnyRef[T: Manifest] = List(
   manifest[T] <:< manifest[Any],
   manifest[T] <:< manifest[AnyRef],
   !(manifest[T] <:< manifest[AnyVal])
 ) foreach (assert(_, "assertAnyRef"))

 def assertAnyVal[T: Manifest] = List(
   manifest[T] <:< manifest[Any],
   !(manifest[T] <:< manifest[AnyRef]),
   manifest[T] <:< manifest[AnyVal]
 ) foreach (assert(_, "assertAnyVal"))

 def assertSameType[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == SAME, "assertSameType")
 def assertSuperType[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == SUPER, "assertSuperType")
 def assertSubType[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == SUB, "assertSubType")
 def assertNoRelationship[T: Manifest, U: Manifest] = assert(typeCompare[T, U] == NONE, "assertNoRelationship")

 def testVariancesVia[T: Manifest, U: Manifest] = assert(
   typeCompare[T, U] == SUB &&
   showsCovariance[T, U, List] &&
   showsInvariance[T, U, Set],
   "testVariancesVia"
 )

 def runAllTests = {
   assertAnyVal[AnyVal]
   assertAnyVal[Unit]
   assertAnyVal[Int]
   assertAnyVal[Double]
   assertAnyVal[Boolean]
   assertAnyVal[Char]

   assertAnyRef[AnyRef]
   assertAnyRef[java.lang.Object]
   assertAnyRef[java.lang.Integer]
   assertAnyRef[java.lang.Double]
   assertAnyRef[java.lang.Boolean]
   assertAnyRef[java.lang.Character]
   assertAnyRef[String]
   assertAnyRef[scala.List[String]]
   assertAnyRef[scala.List[_]]

   // variance doesn't work yet
   // testVariancesVia[String, Any]
   // testVariancesVia[String, AnyRef]

   assertSubType[List[String], List[Any]]
   assertSubType[List[String], List[AnyRef]]
   assertNoRelationship[List[String], List[AnyVal]]

   assertSubType[List[Int], List[Any]]
   assertSubType[List[Int], List[AnyVal]]
   assertNoRelationship[List[Int], List[AnyRef]]

   // Nothing
   assertSubType[Nothing, Any]
   assertSubType[Nothing, AnyVal]
   assertSubType[Nothing, AnyRef]
   assertSubType[Nothing, String]
   assertSubType[Nothing, List[String]]
   assertSubType[Nothing, Null]
   assertSameType[Nothing, Nothing]

   // Null
   assertSubType[Null, Any]
   assertNoRelationship[Null, AnyVal]
   assertSubType[Null, AnyRef]
   assertSubType[Null, String]
   assertSubType[Null, List[String]]
   assertSameType[Null, Null]
   assertSuperType[Null, Nothing]

   // Any
   assertSameType[Any, Any]
   assertSuperType[Any, AnyVal]
   assertSuperType[Any, AnyRef]
   assertSuperType[Any, String]
   assertSuperType[Any, List[String]]
   assertSuperType[Any, Null]
   assertSuperType[Any, Nothing]

   // Misc unrelated types
   assertNoRelationship[Unit, AnyRef]
   assertNoRelationship[Unit, Int]
   assertNoRelationship[Int, Long]
   assertNoRelationship[Boolean, String]
   assertNoRelationship[List[Boolean], List[String]]
   assertNoRelationship[Set[Boolean], Set[String]]
 }

 def main(args: Array[String]): Unit = runAllTests
}

--
Paul Phillips      | A Sunday school is a prison in which children do
Imperfectionist    | penance for the evil conscience of their parents.
Empiricist         |     -- H. L. Mencken
ha! spill, pupil   |----------* http://www.improving.org/paulp/ *----------

--
Lift, the simply functional web framework http://liftweb.net
Beginning Scala http://www.apress.com/book/view/1430219890
Follow me: http://twitter.com/dpp
Surf the harmonics

On Tue, Mar 02, 2010 at 10:43:51AM -0800, David Pollak wrote:
> First, the hashCodes are never the same between Manifests of the same
> class:
>
> dpp@yak:~$ scala
> Welcome to Scala version 2.8.0.Beta1-prerelease (Java HotSpot(TM) 64-Bit
> Server VM, Java 1.6.0_15).

What? Come on. Next you'll be wondering if we're ever going to get
nixon out of the white house.

scala> val m1 = manifest[String]
m1: Manifest[String] = java.lang.String

scala> val m2 = manifest[String]
m2: Manifest[String] = java.lang.String

scala> m1.hashCode == m2.hashCode
res0: Boolean = true

https://lampsvn.epfl.ch/trac/scala/ticket/2838
"manifest overrides equals without hashCode"

Changed 5 weeks ago by extempore ¶

* status changed from new to closed
* resolution set to fixed

(In [20728]) Added hashCode implementations to Manifest types where necessary. Closes #2838. No review.

> scala> val m3 = manifest[List[Int]]
> m3: Manifest[List[Int]] = scala.collection.immutable.List[Int]
>
> scala> val m4 = manifest[List[String]]
> m4: Manifest[List[String]] =
> scala.collection.immutable.List[java.lang.String]
>
> scala> m3 == m4
> res1: Boolean = true

OK, that looks busted. In the future opening a ticket would be
appreciated, there is already way too much "report the bug on the
mailing list for faster attention" traffic and it's counterproductive.

On Tue, Mar 2, 2010 at 11:00 AM, Paul Phillips <paulp@improving.org> wrote:

On Tue, Mar 02, 2010 at 10:43:51AM -0800, David Pollak wrote:
> First, the hashCodes are never the same between Manifests of the same
> class:
>
> dpp@yak:~$ scala
> Welcome to Scala version 2.8.0.Beta1-prerelease (Java HotSpot(TM) 64-Bit
> Server VM, Java 1.6.0_15).

What? Come on.  Next you'll be wondering if we're ever going to get
nixon out of the white house.

Nixon's in the whitehouse... what happened to JFK? ;-)
 

scala> val m1 = manifest[String]
m1: Manifest[String] = java.lang.String

scala> val m2 = manifest[String]
m2: Manifest[String] = java.lang.String

scala> m1.hashCode == m2.hashCode
res0: Boolean = true

https://lampsvn.epfl.ch/trac/scala/ticket/2838
"manifest  overrides equals without hashCode"

Changed 5 weeks ago by extempore ś

   * status changed from new to closed
   * resolution set to fixed

(In [20728]) Added hashCode implementations to Manifest types where necessary. Closes #2838. No review.

> scala> val m3 = manifest[List[Int]]
> m3: Manifest[List[Int]] = scala.collection.immutable.List[Int]
>
> scala> val m4 = manifest[List[String]]
> m4: Manifest[List[String]] =
> scala.collection.immutable.List[java.lang.String]
>
> scala> m3 == m4
> res1: Boolean = true

OK, that looks busted.  In the future opening a ticket would be
appreciated, there is already way too much "report the bug on the
mailing list for faster attention" traffic and it's counterproductive.

Will do.
 

--
Paul Phillips      | Where there's smoke, there's mirrors!
Analgesic          |
Empiricist         |
i pull his palp!   |----------* http://www.improving.org/paulp/ *----------

--
Lift, the simply functional web framework http://liftweb.net
Beginning Scala http://www.apress.com/book/view/1430219890
Follow me: http://twitter.com/dpp
Surf the harmonics

Also, the equals outcome is already documented behavior:

/** Tests whether the type represented by this manifest is equal to the
* type represented by `that' manifest. BE AWARE: the current
* implementation is an approximation, as the test is done on the
* erasure of the type. */

So I think I can improve it but it's "performing as specified."