Function array_subscript_fetch

src/backend/utils/adt/arraysubs.c:235–254

* Evaluate SubscriptingRef fetch for an array element. * * Source container is in step's result variable (it's known not NULL, since * we set fetch_strict to true), and indexes have already been evaluated into * workspace array. */

 * workspace array.
 */
static void
array_subscript_fetch(ExprState *state,
					  ExprEvalStep *op,
					  ExprContext *econtext)
{
	SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
	ArraySubWorkspace *workspace = (ArraySubWorkspace *) sbsrefstate->workspace;

	/* Should not get here if source array (or any subscript) is null */
	Assert(!(*op->resnull));

	*op->resvalue = array_get_element(*op->resvalue,
									  sbsrefstate->numupper,
									  workspace->upperindex,
									  workspace->refattrlength,
									  workspace->refelemlength,
									  workspace->refelembyval,
									  workspace->refelemalign,
									  op->resnull);
}

/*
 * Evaluate SubscriptingRef fetch for an array slice.