Re: Can't access record attribute in derived type

[Mart van de Wege <mvdwege@gmail.com>]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> I suspect we'll need to see a more complete example to definitively say what 
> the problem is.
>
The full code lives at https://github.com/mvdwege/pendragon

Note that some stuff is in incomplete branches, and I still have some
locally committed changes that are not in the github repo. The code that
was throwing errors among them.

> But if I had to guess, I'd suggest that you've run afoul of the "sibling 
> inheritance problem". The rule for visibility for child components is that 
> *all* of components of the *all* of the ancestors have to be visible at the 
> point of declaration of the child type. If even one of the ancestors is not 
> visible (as happens when deriving from a type defined in a sibling child 
> package), then the components aren't visible, either.
>
It appears that that is it. While Knights is a descendant of Person, the
Knights package is indeed a sibling of Persons, not a child.

I failed to let my package design keep up with the actual design of the
objects.

The problem went away when I moved the Knights definition into the
Persons package. Now I know why.

(In fact, my original design had a wild growth of child packages which I
was in the process of pruning back as being excessively complex. Which
probably caused my confusion above).

> Note that in such a case, if you have visiblity on some but not all of the 
> ancestors, you can type convert the object to make them visible. In your 
> example above:
>
>      return Creature(K).Parents.First_Element;

Yes, using conversions in my unit tests suppressed other errors I
couldn't get, and now I understand why those conversions were
necessary.

Mart

-- 
"We will need a longer wall when the revolution comes."
    --- AJS, quoting an uncertain source.