Re: What would you like in Ada202X?

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Sun, 29 Apr 2012 21:04:34 +0200, Robert A Duff
<bobduff@shell01.theworld.com> a écrit:

> okellogg@users.sourceforge.net writes:
>
>> Could you elaborate?
>
> package P is
>     package Q is
>     private
>     end Q;
> private
> end P;
>
> package body P is
>     package body Q is
>     end Q;
> end P;
>
> In the above nested case:
> P spec can see things in Q spec (imagine all sorts of declarations
>  at various places above).

Yes, and that's useful to define a set of preliminary types needed for the
definition of a type, which is to be defined in P. Then, I like to do it
all in Q, avoiding overlong and bloated name which would inevitably be  
there
if ever another types follow some similar pattern in P. Unfortunately, if
you do this, you cannot give Q any child packages, and if you make Q a
child package, it cannot anymore access stuff already defined in p.

package P

      type Comment_Type …;

      package Q1
         type Role1_Type;
         type Role2_Type;
         type Uuseful_Type;
         -- Useful type defined based on role 1 and role 2
         -- and common type.
      end Q1;

      subtype Some_Type is Q1.Useful_Type;

      package Q2
         type Role1_Type;
         type Role2_Type;
         type Useful_Type;
         -- Note how the pattern is the same as in Q1.
      end Q2;

      subtype Another_Type is Q2.Useful_Type;

end P;

Without Q1 and Q2, you would have to give so much different names that the  
common pattern would be less clear, or else would have to use prefix like  
“Q1_” or “Q2_”, which in turn suggest to use nested or child packages.

Not a general case example, just a case I remember.

-- 
“Syntactic sugar causes cancer of the semi-colons.” [1]
“Structured Programming supports the law of the excluded muddle.” [1]
[1]: Epigrams on Programming — Alan J. — P. Yale University