Function deconstruct_expanded_array

src/backend/utils/adt/array_expanded.c:423–453

* Create the Datum/isnull representation of an expanded array object * if we didn't do so previously */

 * if we didn't do so previously
 */
void
deconstruct_expanded_array(ExpandedArrayHeader *eah)
{
	if (eah->dvalues == NULL)
	{
		MemoryContext oldcxt = MemoryContextSwitchTo(eah->hdr.eoh_context);
		Datum	   *dvalues;
		bool	   *dnulls;
		int			nelems;

		dnulls = NULL;
		deconstruct_array(eah->fvalue,
						  eah->element_type,
						  eah->typlen, eah->typbyval, eah->typalign,
						  &dvalues,
						  ARR_HASNULL(eah->fvalue) ? &dnulls : NULL,
						  &nelems);

		/*
		 * Update header only after successful completion of this step.  If
		 * deconstruct_array fails partway through, worst consequence is some
		 * leaked memory in the object's context.  If the caller fails at a
		 * later point, that's fine, since the deconstructed representation is
		 * valid anyhow.
		 */
		eah->dvalues = dvalues;
		eah->dnulls = dnulls;
		eah->dvalueslen = eah->nelems = nelems;
		MemoryContextSwitchTo(oldcxt);
	}
}