Using 'return List<T>(std::move(dynList))' for transfer of content
  (with implicit shrinking) into a plain List, and leave copy elision
  to do the rest. The implicit transfer (move construct List from
  DynamicList) will normally invoke resize (new/delete and moving
  elements).

  With 'return dynList.shrink()', it will first invoke an internal
  resize (new/delete and moving elements), followed by a copy
  construct as a plain list.

STYLE: avoid implicit cast to 'const List&' in constructors