Gives C access into the internal storage of the ARRAY.
Result is pointing the element at index lower.
NOTE: do not free/realloc the Result. Any operation that changes
lower or upper can make this pointer useless (because the
array has wrapped or its beginning in the storage has moved),
and operations that change capacity can make it invalid
(because new memory has been allocated and the old memory has
For performance reasons, the unused area of storage is always left as it is when
some elements are removed.
No time is lost to clean the released area with a Void
or a 0 value. (Look for example the remove_last implementation.)
Thus, the unused area of storage may contains references of actually unreachable
objects. The following mark_native_arrays actually replace the
default behavior (the call is automatic) in order to mark only reachable objects.
To be used _only_ inside the definition of mark_native_arrays.
Forces the garbage collector to continue the marking process on the index-th element of
the native_array. The element at index can be Void or not Void (the Void-ness test is
performed inside the mark_item itself).