Function left_oper

src/backend/parser/parse_oper.c:529–603

left_oper() -- search for a unary left operator (prefix operator) * Given operator name and type of arg, return oper struct. * * IMPORTANT: the returned operator (if any) is only promised to be * coercion-compatible with the input datatype. Do not use this if * you need an exact- or binary-compatible match. * * If no matching operator found, return NULL if noError is true, * raise an erro

 * must ReleaseSysCache() the entry when done with it.
 */
Operator
left_oper(ParseState *pstate, List *op, Oid arg, bool noError, int location)
{
	Oid			operOid;
	OprCacheKey key;
	bool		key_ok;
	FuncDetailCode fdresult = FUNCDETAIL_NOTFOUND;
	HeapTuple	tup = NULL;

	/*
	 * Try to find the mapping in the lookaside cache.
	 */
	key_ok = make_oper_cache_key(pstate, &key, op, InvalidOid, arg, location);

	if (key_ok)
	{
		operOid = find_oper_cache_entry(&key);
		if (OidIsValid(operOid))
		{
			tup = SearchSysCache1(OPEROID, ObjectIdGetDatum(operOid));
			if (HeapTupleIsValid(tup))
				return (Operator) tup;
		}
	}

	/*
	 * First try for an "exact" match.
	 */
	operOid = OpernameGetOprid(op, InvalidOid, arg);
	if (!OidIsValid(operOid))
	{
		/*
		 * Otherwise, search for the most suitable candidate.
		 */
		FuncCandidateList clist;

		/* Get prefix operators of given name */
		clist = OpernameGetCandidates(op, 'l', false);

		/* No operators found? Then fail... */
		if (clist != NULL)
		{
			/*
			 * The returned list has args in the form (0, oprright). Move the
			 * useful data into args[0] to keep oper_select_candidate simple.
			 * XXX we are assuming here that we may scribble on the list!
			 */
			FuncCandidateList clisti;

			for (clisti = clist; clisti != NULL; clisti = clisti->next)
			{
				clisti->args[0] = clisti->args[1];
			}

			/*
			 * We must run oper_select_candidate even if only one candidate,
			 * otherwise we may falsely return a non-type-compatible operator.
			 */