Scala error: type arguments do not conform to class type parameter bounds

Question

See the following function definition:

class Entity[T](
               val pi : T => String,
               val si : T => Map[Symbol,String],
               val tag : ClassTag[T],
               val address: T=>AnyRef
) {
      // some other definitions here ... 
      def filterEntity(attribute: DiscreteAttribute[T], value: String ):Unit={
         // nothing 
      }

}

The compiler gives me the following error:

/Users/i-danielk/ideaProjects/saul/src/main/scala/edu/illinois/cs/cogcomp/lfs/data_model/entity/Entity.scala:67: type arguments [T] do not conform to class DiscreteAttribute's type parameter bounds [T <: AnyRef]
[error]   def filterEntity(attribute: DiscreteAttribute[T], value: String ):Entity[T]={

And here is the definition of the DiscreteAttribute:

case class DiscreteAttribute[T <: AnyRef](
                                 val name : String,
                                 val mapping: T => String,
                                 val range : Option[List[String]]
                                 )(implicit val tag : ClassTag[T]) extends TypedAttribute[T,String]{
....
}

Any idea where I am going wrong?

Update: The following does not work either:

def filterEntity(attribute: DiscreteAttribute[T <: AnyRef], value: String ):Entity[T]={

Here is the error:

 /Users/i-danielk/ideaProjects/saul/src/main/scala/edu/illinois/cs/cogcomp/lfs/data_model/entity/Entity.scala:67: ']' expected but '<:' found.
[error]   def filterEntity(attribute: DiscreteAttribute[T <: AnyRef], value: String ):Entity[T]={

Update2: here is how it's been used:

   val filteredConstituent= EdisonDataModel.constituents.filterEntity(EdisonDataModel.Eview,"Token")

where

object EdisonDataModel extends DataModel {
  val Eview = discreteAttributeOf[Constituent]('CviewName){
    x=>x.getViewName
}

and

  def discreteAttributeOf[T <: AnyRef](name : Symbol)(f : T => String)(implicit tag : ClassTag[T]) : DiscreteAttribute[T] = {
   new DiscreteAttribute[T](name.toString,f,None)
  }

Update 3: The same error holds for the following function definition:

  def filterEntity(attribute: DiscreteAttribute[T], value: String ):Unit={
      // empty 
  }

Your code sample here is incomplete. Post the defining environment of filterEntity — Daenyth
– Daenyth, Commented Sep 17, 2015 at 18:16

Aldo Stracquadanio · Accepted Answer · 2015-09-17 18:40:37Z

6

You need to define a restriction for the T type that is affecting the filterEntity method.

e.g. class Something[T <: AnyRef] so that it matches the restriction on DiscreteAttribute

In your case you want to have the declaration of Entity as: class Entity[T <: AnyRef].

edited Sep 17, 2015 at 18:40

Aldo Stracquadanio

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answered Sep 17, 2015 at 17:45

emilianogc

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4 Comments

Daniel Over a year ago

See this does not work either: def filterEntity(attribute: DiscreteAttribute[T <: AnyRef], value: String ):Entity[T]={

emilianogc Over a year ago

You need to change it not in the usage but the definition. See comments on the question saying that your example is incomplete.

Daniel Over a year ago

I completed the definition of the function (the first code). Any idea?

emilianogc Over a year ago

But where is the type T coming from? I'm guessing the class that contains the filterEntity method is defined.

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