Selectively disable subsumption in Scala? (correctly type List.contains)

Question

List(\"a\").contains(5)

Because an Int can never be contained in a list of String

Answer 1

In my library extension I use:

class TypesafeEquals[A](val a: A) {
  def =*=(x: A): Boolean = a == x
  def =!=(x: A): Boolean = a != x
}
implicit def any2TypesafeEquals[A](a: A) = new TypesafeEquals(a)


class RichSeq[A](val seq: Seq[A]) { 
  ...
  def containsSafely(a: A): Boolean = seq exists (a =*=)
  ...
}
implicit def seq2RichSeq[A](s: Seq[A]) = new RichSeq(s)

So I avoid calling contains.