static <A> int[] indicesOf_array(L<A> l, A a) {
  if (l == null) null;
  
  ifclass IContentsIndexedList
  if (l cast IContentsIndexedList)
    ret i.indicesOf(a);
  endif
  
  new L<Int> x;
  for (int i = 0; i < l(l); i++)
    if (eq(l.get(i), a))
      x.add(i);
  ret toIntArray(x);
}

Began life as a copy of #1025514