Function array_exec_setup

src/backend/utils/adt/arraysubs.c:472–528

* Set up execution state for an array subscript operation. */

 * Set up execution state for an array subscript operation.
 */
static void
array_exec_setup(const SubscriptingRef *sbsref,
				 SubscriptingRefState *sbsrefstate,
				 SubscriptExecSteps *methods)
{
	bool		is_slice = (sbsrefstate->numlower != 0);
	ArraySubWorkspace *workspace;

	/*
	 * Enforce the implementation limit on number of array subscripts.  This
	 * check isn't entirely redundant with checking at parse time; conceivably
	 * the expression was stored by a backend with a different MAXDIM value.
	 */
	if (sbsrefstate->numupper > MAXDIM)
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("number of array dimensions (%d) exceeds the maximum allowed (%d)",
						sbsrefstate->numupper, MAXDIM)));

	/* Should be impossible if parser is sane, but check anyway: */
	if (sbsrefstate->numlower != 0 &&
		sbsrefstate->numupper != sbsrefstate->numlower)
		elog(ERROR, "upper and lower index lists are not same length");

	/*
	 * Allocate type-specific workspace.
	 */
	workspace = (ArraySubWorkspace *) palloc(sizeof(ArraySubWorkspace));
	sbsrefstate->workspace = workspace;

	/*
	 * Collect datatype details we'll need at execution.
	 */
	workspace->refelemtype = sbsref->refelemtype;
	workspace->refattrlength = get_typlen(sbsref->refcontainertype);
	get_typlenbyvalalign(sbsref->refelemtype,
						 &workspace->refelemlength,
						 &workspace->refelembyval,
						 &workspace->refelemalign);

	/*
	 * Pass back pointers to appropriate step execution functions.
	 */
	methods->sbs_check_subscripts = array_subscript_check_subscripts;
	if (is_slice)
	{
		methods->sbs_fetch = array_subscript_fetch_slice;
		methods->sbs_assign = array_subscript_assign_slice;
		methods->sbs_fetch_old = array_subscript_fetch_old_slice;
	}
	else
	{
		methods->sbs_fetch = array_subscript_fetch;
		methods->sbs_assign = array_subscript_assign;
		methods->sbs_fetch_old = array_subscript_fetch_old;
	}
}