Double Definition Error Despite Different Parameter Types

Question

I\'m receiving a double definition error on the following two methods:

def apply[T](state: T, onRender: T => Graphic,
             onMouseEvent: (MouseEvent,          


        

Answer 1

Here's a simpler example that shows the same issue:

object Example {
  def foo[T](f: Int => T) = ???
  def foo[T](f: String => T) = ???
}

This is equivalent to the following, after desugaring the => symbols:

object Example {
  def foo[T](f: Function[Int, T]) = ???
  def foo[T](f: Function[String, T]) = ???
}

The problem is that the Java Virtual Machine doesn't know about generics (in either Scala or Java), so it sees these two methods as the following:

object Example {
  def foo[T](f: Function) = ???
  def foo[T](f: Function) = ???
}

Which is clearly a problem.

This is one of many reasons to avoid method overloading in Scala. If that's not an option, you could use a trick like the following:

object Example {
  implicit object `Int => T disambiguator`
  implicit object `String => T disambiguator`

  def foo[T](f: Int => T)(implicit d: `Int => T disambiguator`.type) = ???
  def foo[T](f: String => T)(implicit d: `String => T disambiguator`.type) = ???
}

Which looks the same usage-wise, but is obviously pretty hideous.