TreeMap update keeps old key

[lrytz]

Not a bug? This made a test in play's test suite fail.

scala> object CaseInsensitiveOrdered extends Ordering[String] {
     |   def compare(x: String, y: String): Int = {
     |     val xl = x.length
     |     val yl = y.length
     |     if (xl < yl) -1 else if (xl > yl) 1 else x.compareToIgnoreCase(y)
     |   }
     | }

scala> val m = scala.collection.immutable.TreeMap[String, String]()(CaseInsensitiveOrdered)

scala> m ++ Seq("a" -> "1", "A" -> "2")
res1: scala.collection.immutable.TreeMap[String,String] = TreeMap(a -> 2)

[lrytz]

it's probably a feature, not a bug. scala/scala#7481

[lrytz]

When updating a collection (immutably or in place), key element identities already in the source collection (i.e. the receiver of a method call) must always be preferred over new key elements which are equal but have different identities.