public IEnumerator<ReadOnlySegmentCollection> GetEnumerator()

{
  ReadOnlyPartCollection polylineParts = polyline.Parts;

  // enumerate the segments to get the length
  double len = 0;
  IEnumerator<ReadOnlySegmentCollection> segmentsPolyline = polylineParts.GetEnumerator();
  while (segmentsPolyline.MoveNext())
  {
    ReadOnlySegmentCollection seg = segmentsPolyline.Current;
    foreach (Segment s in seg)
    {
      len += s.Length;

      // perhaps do something specific per segment type
      switch (s.SegmentType)
      {
        case SegmentType.Line:
          break;
        case SegmentType.Bezier:
          break;
        case SegmentType.EllipticArc:
          break;
      }
    }
  }

  // or use foreach pattern
  foreach (var part in polyline.Parts)
  {
    foreach (var segment in part)
    {
      len += segment.Length;

      // perhaps do something specific per segment type
      switch (segment.SegmentType)
      {
        case SegmentType.Line:
          break;
        case SegmentType.Bezier:
          break;
        case SegmentType.EllipticArc:
          break;
      }
    }
  }
}