Why isn't there a lengthCompare method on Scala Set?

Question

In Scala Seq, there is a lengthCompare method which returns the comparison between the Seq length and a given Int without computing the length of the Seq.

It is implemented in the trait SeqLike as follows:

/** Compares the length of this $coll to a test value.
   *
   *   @param   len   the test value that gets compared with the length.
   *   @return  A value `x` where
   *   {{{
   *        x <  0       if this.length <  len
   *        x == 0       if this.length == len
   *        x >  0       if this.length >  len
   *   }}}
   *  The method as implemented here does not call `length` directly; its running time
   *  is `O(length min len)` instead of `O(length)`. The method should be overwritten
   *  if computing `length` is cheap.
   */
  def lengthCompare(len: Int): Int = {
    if (len < 0) 1
    else {
      var i = 0
      val it = iterator
      while (it.hasNext) {
        if (i == len) return if (it.hasNext) 1 else 0
        it.next()
        i += 1
      }
      i - len
    }
  }

Since this implementation only requires an iterator, why isn't it defined in IterableLike?

That would make it available in Seq, Set and Map collections.

Answer 1

There is one in the new and greatly overhauled Scala 2.13 collections that was released just yesterday, see here. The simple reason is that plenty of things about the Scala collections just weren't the way they ought to be, which has now been fixed. The fact that it exists in the new version indicates that it wasn't an active choice to exclude it previously.