Function transformContainerSubscripts

src/backend/parser/parse_node.c:247–331

* transformContainerSubscripts() * Transform container (array, etc) subscripting. This is used for both * container fetch and container assignment. * * In a container fetch, we are given a source container value and we produce * an expression that represents the result of extracting a single container * element or a container slice. * * Container assignments are treated basically the sa

 * isAssignment		True if this will become a container assignment.
 */
SubscriptingRef *
transformContainerSubscripts(ParseState *pstate,
							 Node *containerBase,
							 Oid containerType,
							 int32 containerTypMod,
							 List *indirection,
							 bool isAssignment)
{
	SubscriptingRef *sbsref;
	const SubscriptRoutines *sbsroutines;
	Oid			elementType;
	bool		isSlice = false;
	ListCell   *idx;

	/*
	 * Determine the actual container type, smashing any domain.  In the
	 * assignment case the caller already did this, since it also needs to
	 * know the actual container type.
	 */
	if (!isAssignment)
		transformContainerType(&containerType, &containerTypMod);

	/*
	 * Verify that the container type is subscriptable, and get its support
	 * functions and typelem.
	 */
	sbsroutines = getSubscriptingRoutines(containerType, &elementType);
	if (!sbsroutines)
		ereport(ERROR,
				(errcode(ERRCODE_DATATYPE_MISMATCH),
				 errmsg("cannot subscript type %s because it does not support subscripting",
						format_type_be(containerType)),
				 parser_errposition(pstate, exprLocation(containerBase))));

	/*
	 * Detect whether any of the indirection items are slice specifiers.
	 *
	 * A list containing only simple subscripts refers to a single container
	 * element.  If any of the items are slice specifiers (lower:upper), then
	 * the subscript expression means a container slice operation.
	 */
	foreach(idx, indirection)
	{
		A_Indices  *ai = lfirst_node(A_Indices, idx);

		if (ai->is_slice)
		{
			isSlice = true;
			break;
		}
	}

	/*
	 * Ready to build the SubscriptingRef node.
	 */
	sbsref = makeNode(SubscriptingRef);

	sbsref->refcontainertype = containerType;