Constrained variables cannot be edited in-place

Typically it's not possible to edit variables in-place when complicated integrity constraints are imposed.

For example, it's usually not possible to edit text in-place if there's a constraint that it conforms to a grammar as it is edited - i.e. as the user types on a keyboard and inserts or deletes individual characters.

For example how would the user add another member

    int z;

without transitioning through invalid states while typing the characters?