CODEWITHSUNDEEP
scalaimplicit
Abdul Rahman
Abdul Rahman

Reputation: 1384

Unable to find implicit value

So my code looks as follows

    package typeclasses

    trait Eq[T]{

      def == (t1: T, t2: T) : Boolean
    }

    case class MyClass()

    object MyClass {

      implicit object EqMyClass extends Eq[MyClass] {
        override def ==(t1: MyClass, t2: MyClass): Boolean = true
      }
    }

    object App1 extends App{

      import Tree._
      import MyClass._

      def equality[T](t1: T, t2: T)(implicit eq: Eq[T]): Boolean = eq.==(t1, t2)

      //println(equality(Node(1), Node(2)))

      println(equality(MyClass, MyClass))
    }

However I get the error that compiler is unable to find implicit value for Eq[MyClass]. Here is the error that I get. 

Error:(38, 19) could not find implicit value for parameter eq: typeclasses.Eq[typeclasses.MyClass.type]
  println(equality(MyClass, MyClass))

Shouldn't it have found Eq[MyClass] since I import the MyClass object into App1 and have EqMyClass defined in there? Also do I even need to import MyClass object into App1? My understanding was that scala looks at companion objects of arg types to find implicit defs?

Thanks!

Upvotes: 1

Views: 189

Answers (1)

Fabian Schmitthenner
Fabian Schmitthenner

Reputation: 1706

you have to write println(equality(MyClass(), MyClass()) since MyClass is the companion object (of type MyClass.type) instead of an instance of MyClass.

Upvotes: 3

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