ALF_ — Indexed feature left hand sides

Subject: Indexed feature left hand sides

Subclauses: 13.2.18 FeatureLeftHandSide, 13.2.35 NameLeftHandSide

In a FeatureLeftHandSide, if the left-hand side has an index, then the referenced feature must be a sequence (simply being ordered is not enough for the “replace” semantics of indexed assignment). Since a similar constraint is required for a NameLeftHandSide with an index, if the name

disambiguates to a feature, the constraint is probably best handled in a unified way in the LeftHandSide superclass.

To handle this constraint in a unified way in LeftHandSide superclass would probably require adding a derived referent property to be used for it, as well as adding derivations for it in each subclass. It is simpler instead to just add to each subclass the specific constraints necessary to resolve the issue.