+
+ # define and set xcb_listelement, so that it can be used by
+ # listelement-ref expressions.
+ if expr.contains_listelement_ref:
+ _c_pre.code(
+ "const %s *xcb_listelement = %s;",
+ field.c_field_type, listvar)
+
+ # summation
+ if expr.rhs is None:
+ _c_pre.code("%s += *%s;", sumvar, listvar)
+ else:
+ # sumof has a nested expression which has to be evaluated in
+ # the context of this list element
+
+ # field mapping for the subexpression needs to include
+ # the fields of the list-member type
+ scoped_field_mapping = field_mapping.copy()
+ if not field.type.member.is_simple:
+ scoped_field_mapping.update(
+ _c_helper_field_mapping(
+ field.type.member,
+ [(listvar, '->', field.type.member)]))
+
+ # cause pre-code of the subexpression be added right here
+ _c_pre.end()
+ # compute the subexpression
+ rhs_expr_str = _c_accessor_get_expr(expr.rhs, scoped_field_mapping)
+ # resume with our code
+ _c_pre.start()
+ # output the summation expression
+ _c_pre.code("%s += %s;", sumvar, rhs_expr_str)
+