ALF_ — AssignmentExpression as a data value update

Subject: AssignmentExpression as a data value update

Subclause: 13.2.2 AssignmentExpression,

· An assignment expression should only be allowed to be a data value update if its left hand side is a feature reference whose primary expression is a local name or parameter name.

· The derivation of the assignment for an assignment expression needs to account for the cases of a data value update and an indexed left hand side.

The deriviation of isDataValueUpdate is such that it is true only in the case mentioned in the first bullet. However, nothing currently prevents assignment to an attribute of a data type where the primary expression of the feature reference is not a local name or parameter. Such an assignment will not be mapped correctly, because it will not be considered a data value update and, so, the updated data value will be lost. Therefore, this case should be disallowed.
In the case of a data value update for an indexed left-hand side, the multiplicity of the new assignment should not be that of the left-hand side (which will be 1) but, rather, should be * (since only a sequence can be indexed).