Scala path dependent return type from parameter

Question

In the following code using 2.10.0M3 in Eclipse plugin 2.1.0 for 2.10M3. I'm using the default setting which is targeting JVM 1.5

class GeomBase[T <: DTypes] {          
  abstract class NewObjs {
    def newHex(gridR: GridBase, coodI: Cood): gridR.HexRT          
  }

  class GridBase {
    selfGrid =>
      type HexRT = HexG with T#HexTr

    def uniformRect (init: NewObjs) {
      val hexCood = Cood(2 ,2)
      val hex: HexRT = init.newHex(selfGrid, hexCood)//  won't compile
    }
  }
}

Error message:

Description Resource Path Location Type type mismatch;
  found: GeomBase.this.GridBase#HexG with T#HexTr
  required: GridBase.this.HexRT (which expands to) GridBase.this.HexG with T#HexTr GeomBase.scala

Why does the compiler think the method returns the type projection GridBase#HexG when it should be this specific instance of GridBase?

Edit transferred to a simpler code class in responce to comments now getting a different error message.

package rStrat
class TestClass {
  abstract class NewObjs {
    def newHex(gridR: GridBase): gridR.HexG
  }     
  class GridBase {
    selfGrid =>         

    def uniformRect (init: NewObjs) {
      val hex: HexG = init.newHex(this) //error here                        
    }       

    class HexG {
      val test12 = 5                 
    }
  }
}

.

Error line 11:Description   Resource    Path    Location    Type
type mismatch;  found   : gridR.HexG  required: GridBase.this.HexG
possible cause: missing arguments for method or constructor TestClass.scala /SStrat/src/rStrat  line 11 Scala Problem

Update I've switched to 2.10.0M4 and updated the plug-in to the M4 version on a fresh version of Eclipse and switched to JVM 1.6 (and 1.7) but the problems are unchanged.

could you please add a working code example which produces the error message? — kiritsuku
You should paste the source code line with the error and the arrow that points to the exact location of the error that are also displayed. — Daniel C. Sobral
@RichOliver There should still be lines below that error. The line of code with the error itself, and, below it, a line with a single ^ character pointing to the error. — Daniel C. Sobral

Adriaan Moors Adriaan Moors · Accepted Answer · 2012-06-21T07:50:26

4

votes

logged as SI-5958 - substitute this in dependent method type

Scala path dependent return type from parameter

2 Answers