Function initArrayResultArr

src/backend/utils/adt/arrayfuncs.c:5387–5423

* initArrayResultArr - initialize an empty ArrayBuildStateArr * * array_type is the array type (must be a valid varlena array type) * element_type is the type of the array's elements (lookup if InvalidOid) * rcontext is where to keep working state * subcontext is a flag determining whether to use a separate memory context */

 *	subcontext is a flag determining whether to use a separate memory context
 */
ArrayBuildStateArr *
initArrayResultArr(Oid array_type, Oid element_type, MemoryContext rcontext,
				   bool subcontext)
{
	ArrayBuildStateArr *astate;
	MemoryContext arr_context = rcontext;	/* by default use the parent ctx */

	/* Lookup element type, unless element_type already provided */
	if (!OidIsValid(element_type))
	{
		element_type = get_element_type(array_type);

		if (!OidIsValid(element_type))
			ereport(ERROR,
					(errcode(ERRCODE_DATATYPE_MISMATCH),
					 errmsg("data type %s is not an array type",
							format_type_be(array_type))));
	}

	/* Make a temporary context to hold all the junk */
	if (subcontext)
		arr_context = AllocSetContextCreate(rcontext,
											"accumArrayResultArr",
											ALLOCSET_DEFAULT_SIZES);

	/* Note we initialize all fields to zero */
	astate = (ArrayBuildStateArr *)
		MemoryContextAllocZero(arr_context, sizeof(ArrayBuildStateArr));
	astate->mcontext = arr_context;
	astate->private_cxt = subcontext;

	/* Save relevant datatype information */
	astate->array_type = array_type;
	astate->element_type = element_type;

	return astate;
}

/*
 * accumArrayResultArr - accumulate one (more) sub-array for an array result