Re: semi-visibility

[Jeffrey Carter <spam@spam.com>]

tmoran@acm.org wrote:
> I want to do the following, but it's illegal.  What's a good way to
> accomplish the purpose, preferably without increasing the depth of
> the package heirarchy, or enlarging package A.
> 
> private package A.B is
>   type Visible_To_Relatives is ...
> end A.B;
> 
> with A.B;
> package A.C is
>   type T is private;
>   procedure P(x : in T);
> private
>   type T is record
>     v : A.B.Visible_To_Relatives;
>   end record;
> end A.C;

One solution is to wait for Ada 0X. It has a way to to do this; IIRC, 
it's "with private".

If you need it sooner, one solution is

private
    type T_Implementation;
    type T is access [all] T_Implementation;
end A.C;

This gets you into possible problems with initialization and 
finalization that you might be able to alleviate by using Ada.Finalization.

A simpler solution is to make A.B non-private and attempt to enforce a 
rule that it only be referenced in the private parts and bodies of 
children of A.

-- 
Jeff Carter
"C's solution to this [variable-sized arrays] has real problems,
and people who are complaining about safety definitely have a point."
Dennis Ritchie