Re: Generic-Package Elaboration Question / Possible GNAT Bug.

[Shark8 <onewingedshark@gmail.com>]

On Nov 22, 9:13 pm, Yannick Duchêne (Hibou57)
<yannick_duch...@yahoo.fr> wrote:
> A guess attempt: does not depend on Generic_Delete implementation, but
> rather on a Generic_Delete instantiation parameters. If you could post the
> instantiation snippet too… (with declarations it depends on).
>
> Le Sat, 19 Nov 2011 22:14:44 +0100, Shark8 <onewingedsh...@gmail.com> a
> écrit:
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> > I was working on some simple little array manipulation functions when
> > I encountered an interesting behavior in the compiler; it said that
> > trying to instantiate a function of the form:
> >    Generic
> >       Type Element is Private;
> >       Type Index_Type is (<>);
> >       Type Array_Type is Array (Index_Type Range <>) of Element;
> >    Function Generic_Delete( Index : In Index_Type; Data : In
> > Array_Type ) Return Array_Type;
>
> > When given the following body, the compiler complained about the
> > Index_Range'First/Last not being static:
>
> >    Function Generic_Delete( Index : In Index_Type; Data : In
> > Array_Type ) Return Array_Type is
> >    begin
> >       if Index not in Data'Range then
> >          Raise Constraint_Error;
> >       else
> >            case Index is
> >            when Index_Type'First => Return
> > Data( Index_Type'Succ(Index)..Data'Last );
> >            when Index_Type'Last => Return
> > Data( Data'First..Index_Type'Pred(Index) );
> >            when others =>
> >                   Return Data( Data'First..Index_Type'Pred(Index) )
> >             & Data( Index_Type'Succ(Index)..Data'Last );
> >            end case;
> >       end if;
> >    end Generic_Delete;
>
> > Now, I know that the following works as a fix:
>
> >      Function Generic_Delete( Index : In Index_Type; Data : In
> > Array_Type ) Return Array_Type is
> >      begin
> >         if Index not in Data'Range then
> >            Raise Constraint_Error;
> >         else
> >            if Index = Data'First then
> >               Return Data( Index_Type'Succ(Index)..Data'Last );
> >            elsif Index = Data'Last then
> >               Return Data( Data'First..Index_Type'Pred(Index) );
> >            else
> >               Return Data( Data'First..Index_Type'Pred(Index) )
> >             & Data( Index_Type'Succ(Index)..Data'Last );
> >            end if;
> >         end if;
> >      end Generic_Delete;
>
> > But the question that came to my mind after reading the ARM section on
> > the error (sorry, I forgot to write it down) is, why is it not static?
> > Is it because though the elaboration-parameters *may* be known [and
> > static] at compile-time that some instantiation might NOT be
> > [guaranteed] to be known at compile-time? (i.e. because the compiler
> > cannot guarantee that you won't throw 1..N where N is something pulled
> > from the user-input?)
>
> --
> “Syntactic sugar causes cancer of the semi-colons.”  [Epigrams on
> Programming — Alan J. — P. Yale University]
> “Structured Programming supports the law of the excluded muddle.” [Idem]

The type I was using were something like:
SubType Board_Index is Positive Range 1..9;
Type Column is Array( Board_Index Range <> ) of Board_Index;


So the instantiation was something like:
 Function Delete is New Generic_Delete( Board_Index, Board_Index,
Column );