Function array_agg_transfn

src/backend/utils/adt/array_userfuncs.c:477–521

* ARRAY_AGG(anynonarray) aggregate function */

 * ARRAY_AGG(anynonarray) aggregate function
 */
Datum
array_agg_transfn(PG_FUNCTION_ARGS)
{
	Oid			arg1_typeid = get_fn_expr_argtype(fcinfo->flinfo, 1);
	MemoryContext aggcontext;
	ArrayBuildState *state;
	Datum		elem;

	if (arg1_typeid == InvalidOid)
		ereport(ERROR,
				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
				 errmsg("could not determine input data type")));

	/*
	 * Note: we do not need a run-time check about whether arg1_typeid is a
	 * valid array element type, because the parser would have verified that
	 * while resolving the input/result types of this polymorphic aggregate.
	 */

	if (!AggCheckCallContext(fcinfo, &aggcontext))
	{
		/* cannot be called directly because of internal-type argument */
		elog(ERROR, "array_agg_transfn called in non-aggregate context");
	}

	if (PG_ARGISNULL(0))
		state = initArrayResult(arg1_typeid, aggcontext, false);
	else
		state = (ArrayBuildState *) PG_GETARG_POINTER(0);

	elem = PG_ARGISNULL(1) ? (Datum) 0 : PG_GETARG_DATUM(1);

	state = accumArrayResult(state,
							 elem,
							 PG_ARGISNULL(1),
							 arg1_typeid,
							 aggcontext);

	/*
	 * The transition type for array_agg() is declared to be "internal", which
	 * is a pass-by-value type the same size as a pointer.  So we can safely
	 * pass the ArrayBuildState pointer through nodeAgg.c's machinations.
	 */
	PG_RETURN_POINTER(state);
}

Datum
array_agg_finalfn(PG_FUNCTION_ARGS)