scala - Override trait's generic method without casting -

i planning have trait "value" attribute can extended multiple classes. need able compare different instances of trait between each other. firstly want check value defined on trait - if thats same across 2 instances, want trigger child-specific method compare 2 child instances of same type each other.

i hope explained enough...

i have below code written, childone class doesnt compile - error getting:

class childone needs abstract, since method childcheck in trait parenttype of type (other: childone.this.t)boolean not defined (note parenttype.this.t not match com.cards.childone)

trait parenttype {   val value: int   type t <: parenttype    def parentcheck(other: t): boolean = {     if (this.value == other.value) childcheck(other)     else this.value > other.value   }    def childcheck(other: t): boolean }  case class childone(name: string) extends parenttype {   val value = 1    override def childcheck(other: childone): boolean = {     true //some custom logic each child...   }  } 

i change parameter of child's method parenttype , cast it, wanted avoid , wondering there better way of doing want achieve?

any appreciated.

you declare abstract type t in parenttype, without overriding in childone. can fix overriding t in chileone:

case class childone(name: string) extends parenttype {   val value = 1   override type t = childone  // <----    override def childcheck(other: childone): boolean = {     true //some custom logic each child...   } }