Ambiguous reference to overloaded definition with =:=

Question
1

Hi,

I’m trying to understand how this compilation error can occur:

  class Foo[T](value: T) {
    def bar           (implicit ev: T =:= String)                   : String = value.asInstanceOf[String].toUpperCase

    def baz(that: Int)(implicit ev: T =:= Int)                      : Int    = value.asInstanceOf[Int]    + that
    def baz(that: Int)(implicit ev: T =:= Double, di: DummyImplicit): Double = value.asInstanceOf[Double] + that
  }

  // ---------------------------------------------------------------------------
  def main(args: Array[String]): Unit = {
    println(new Foo("hello").bar)
    println(new Foo(3.14)   .baz(1)) // compilation error:
      //ambiguous reference to overloaded definition,
      //both method baz in class Foo of type (that: Int)(implicit ev: Double =:= Double, di: DummyImplicit): Double
      //and  method baz in class Foo of type (that: Int)(implicit ev: Double =:= Int): Int
      //match argument types (Int) and expected result type Any
  }

If I understand the message correctly, it seems to imply that an implicit instance of =:=[Double, Int] can be found. If so, it contradicts my understanding of what =:= is supposed to do.

Any help would be appreciated!

PS: using Scala 2.13.4 here