Implicit Search Odditiies

implicit-search-oddities.scala

// for 2.7.x compatibility
def locally[T](x: T): T = x
def implicitly[T](implicit e: T) = e

object A { 
  implicit val one = 1
}

object Test {   
  locally {
    import A._
    locally {
      // assert(implicitly[Int] == 1) // error: could not find implicit value for parameter e: Int. 
                                     // !!! Why one A.one?
      implicit val one = 2
      assert(implicitly[Int] == 2)
      assert(one == 2)
    }
  }
  
  locally {
    import A._
    assert(implicitly[Int] == 1)
    implicit val one = 2
    assert(implicitly[Int] == 1) // !!! why not 2?. why different from the example above?
    assert(one == 2)
  }
  
  locally {
    import A.one // warning: imported `one' is permanently hidden by definition of value one.
                 // !!! Really?
    assert(implicitly[Int] == 1)
    implicit val one = 2
    assert(implicitly[Int] == 1) // !!! why not 2?
    assert(one == 2)
  }
  
  locally {
    import A.one
    assert(implicitly[Int] == 1)
    implicit val two = 2
    assert(implicitly[Int] == 2) // !!! Not ambiguous in 2.8.0. Ambigous in 2.7.6
  }
  
  locally {
    import A._
    assert(implicitly[Int] == 1)
    implicit val two = 2
    import A.{one => _}
    assert(implicitly[Int] == 2) // !!! Not ambiguous in 2.8.0. Ambiguous in 2.7.6
  }
  
  locally {
    import A.{one => _, _}
    implicit val two = 2
    assert(implicitly[Int] == 2) // not ambiguous in 2.8.0 nor im ambiguous in 2.7.6
  }
  
}

Test