Constraints?

Constraints?

[Simon Wright]

(I think I forgot to post this one, it hasn't appeared here yet; if
duplicated, sorry)

GNAT thinks the code below is OK, Object Ada (special edition)
doesn't.  If OA is right, as I fear it may be, can anyone offer a way
of getting the effect I'm after?

(t is some abstract base container, i is an abstract iterator over
such a container, n is a concrete container, r is a concrete iterator
over an n)

package foo is
    type t is abstract tagged null record;
    type i (f : access t'class) is abstract tagged limited null record;
    type n is new t with null record;
    type r (f : access n) is new i (f) with null record;
    -- OA says foo.ads: Error: line 5 col 37 LRM:3.7(15), Subtype of
    -- discriminant must be statically compatible with subtype of the
    -- corresponding parent discriminant
end foo;

Re: Constraints?

[David C. Hoos, Sr.]

Simon Wright wrote in message ...
>(I think I forgot to post this one, it hasn't appeared here yet; if
>duplicated, sorry)
>
>GNAT thinks the code below is OK, Object Ada (special edition)
>doesn't.  If OA is right, as I fear it may be, can anyone offer a way
>of getting the effect I'm after?
>
>(t is some abstract base container, i is an abstract iterator over
>such a container, n is a concrete container, r is a concrete iterator
>over an n)
>
>package foo is
>    type t is abstract tagged null record;
>    type i (f : access t'class) is abstract tagged limited null record;
>    type n is new t with null record;
>    type r (f : access n) is new i (f) with null record;
>    -- OA says foo.ads: Error: line 5 col 37 LRM:3.7(15), Subtype of
>    -- discriminant must be statically compatible with subtype of the
>    -- corresponding parent discriminant
>end foo;
The real problem is a violation of LRM:3.7(13).
Both compilers will accept the code below.
package foo is
    type t is abstract tagged null record;
    type i (f : access t'class) is abstract tagged limited null record;
    type n is new t with null record;
    type a_n is access all n'class;
    type r (f : a_n) is new i (f) with null record;
end foo;


David C. Hoos, Sr.

Re: Constraints?

[dewar]

In article <x7v7lvkk7f8.fsf@pogner.demon.co.uk>,
> package foo is
>     type t is abstract tagged null record;
>     type i (f : access t'class) is abstract tagged
>                           limited null record;
>     type n is new t with null record;
>     type r (f : access n) is new i (f) with null record;
> end foo;


This is definitely invalid. GNAT says:

foo.ads:5:13: subtype must be compatible with parent
discriminant

Robert Dewar
Ada Core Technologies

-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/       Search, Read, Discuss, or Start Your Own    

Re: Constraints?

[Simon Wright]

"David C. Hoos, Sr." <david.c.hoos.sr@ada95.com> writes:

> Simon Wright wrote in message ...
> >package foo is
> >    type t is abstract tagged null record;
> >    type i (f : access t'class) is abstract tagged limited null record;
> >    type n is new t with null record;
> >    type r (f : access n) is new i (f) with null record;
> >    -- OA says foo.ads: Error: line 5 col 37 LRM:3.7(15), Subtype of
> >    -- discriminant must be statically compatible with subtype of the
> >    -- corresponding parent discriminant
> >end foo;
> The real problem is a violation of LRM:3.7(13).
> Both compilers will accept the code below.
> package foo is
>     type t is abstract tagged null record;
>     type i (f : access t'class) is abstract tagged limited null record;
>     type n is new t with null record;
>     type a_n is access all n'class;
>     type r (f : a_n) is new i (f) with null record;
> end foo;

Thanks for that. I don't quite see what (13) has to do with it?

I think I always get frightened by this sort of thing, cos clearly
(!!) the code I need (which is also acceptable to both compilers) is

package foo is
    type t is abstract tagged null record;
    type i (f : access t'class) is abstract tagged limited null record;
    type n is new t with null record;
    type r (f : access n'class) is new i (f) with null record;
end foo;

Referring to my original, Robert Dewar wrote:

> This is definitely invalid. GNAT says:
> 
> foo.ads:5:13: subtype must be compatible with parent
> discriminant

... so I won't need to report the fact that 3.11B _doesn't_ detect the
error, then!

Re: Constraints?

[dewar]

In article <x7vhfukit5q.fsf@pogner.demon.co.uk>,
  Simon Wright <simon@pogner.demon.co.uk> wrote:
> ... so I won't need to report the fact that 3.11B
> _doesn't_ detect the
> error, then!


Right, no need, this fix is post 3.11b (it is actually
post 3.11b2, which is the final 3.11b release, and is the
one on which 3.11p will be based). We now have all the
3.11b2 builds and 3.11p builds complete, the only remaining
step is to check out the NT packaging, which will be done
the coming week, so this release is finally getting close.

Robert Dewar
Ada Core Technologies

-----------== Posted via Deja News, The Discussion Network ==----------
http://www.dejanews.com/       Search, Read, Discuss, or Start Your Own    

Re: Constraints?

[Steve Todd]

     $$$$ THIS WILL MAKE YOU TONS OF MONEY, AND I'M NOT
           JOKING!!! $$$$$ - Alberta Vocational College - Calgary




        [ Home Page ] [ Follow Ups ] [ Post Followup ] [ Alberta Vocational
College - Calgary Forum ] [ FAQ ]


Posted by jim on September 14, 1998 at 18:25:13:

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Remember, play
FAIRLY and HONESTLY and this will work >> >>




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David C. Hoos, Sr. wrote:

> Simon Wright wrote in message ...
> >(I think I forgot to post this one, it hasn't appeared here yet; if
> >duplicated, sorry)
> >
> >GNAT thinks the code below is OK, Object Ada (special edition)
> >doesn't.  If OA is right, as I fear it may be, can anyone offer a way
> >of getting the effect I'm after?
> >
> >(t is some abstract base container, i is an abstract iterator over
> >such a container, n is a concrete container, r is a concrete iterator
> >over an n)
> >
> >package foo is
> >    type t is abstract tagged null record;
> >    type i (f : access t'class) is abstract tagged limited null record;
> >    type n is new t with null record;
> >    type r (f : access n) is new i (f) with null record;
> >    -- OA says foo.ads: Error: line 5 col 37 LRM:3.7(15), Subtype of
> >    -- discriminant must be statically compatible with subtype of the
> >    -- corresponding parent discriminant
> >end foo;
> The real problem is a violation of LRM:3.7(13).
> Both compilers will accept the code below.
> package foo is
>     type t is abstract tagged null record;
>     type i (f : access t'class) is abstract tagged limited null record;
>     type n is new t with null record;
>     type a_n is access all n'class;
>     type r (f : a_n) is new i (f) with null record;
> end foo;
>
> David C. Hoos, Sr.