Question

Somehow, I can’t seem to correctly implement a SortedMap. Here’s a minimal (non-)working example:

class MyMap[A](t: Map[Long, A]) extends SortedMap[Long, A]  {
  protected val internalMap = TreeMap(t.toArray: _*)

  def -(key: Long) = MyMap(internalMap - key)
  def get(key: Long) = internalMap.get(key)
  def rangeImpl(from: Option[Long], until: Option[Long]) = TreeMap(internalMap.rangeImpl(from, until))
  def iterator = internalMap.iterator
  def ordering = internalMap.ordering
}

But, whatever I pass into the MyMap constructor, calling, for example, its size, always returns 0.

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Addendum: I just copy-pasted the code to a new project, and it worked 8-\ Anyway, let me change the question in order to make it useful: is this the correct way to extend SortedMap?

Answer 1

After adding a couple of missing methods to make it compile, your code worked fine for me:

class MyMap[A](t: Map[Long, A]) extends SortedMap[Long, A]  {
  protected val internalMap = TreeMap(t.toArray: _*)
  def +[B1 >: A](kv: (Long, B1)) = new MyMap(internalMap + kv)
  def -(key: Long) = new MyMap(internalMap - key)
  def get(key: Long) = internalMap.get(key)
  def rangeImpl(from: Option[Long], until: Option[Long]) = internalMap.rangeImpl(from, until)
  def iterator = internalMap.iterator
  def ordering = internalMap.ordering
}

From the REPL:

scala> t
res5: Map[Long,String] = Map(123 -> abc, 456 -> def)

scala> new MyMap(t)
res6: MyMap[String] = Map(123 -> abc, 456 -> def)

scala> res6.size
res7: Int = 2

Am I missing something?