static <A> S renderCollectionBytesPerEntry(Cl<A> l) {
  O[] a = toObjectArray_nonConcurrent(l);
  long arraySize = unsafe_sizeOf(a);
  long payloadSize = guessObjectSize(a)-arraySize;
  
  long fullSize = guessObjectSize(l);
  
  ret "A " + className(l) + " with " + nElements(l) + " uses "
    + formatDoubleRatio(fullSize-payloadSize, l(a), 4) + " bytes per element (full size: " + n2(fullSize) + ", payload: " + n2(payloadSize) + ")";
}