Re: Discriminant ans tagged type ?!

["Tom Grosman" <grosman@aonix.fr>]

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"Tony" <truand.tony@gmail.com> a �crit dans le message de news: 
cc37c7dc-d89b-4f4a-82e3-24941300efb5@k13g2000hse.googlegroups.com...
> On 21 mar, 16:25, Adam Beneschan <a...@irvine.com> wrote:
>> On Mar 21, 1:18 am, Tony <truand.t...@gmail.com> wrote:
>>
>>
>>
>> > On 18 mar, 20:54, Adam Beneschan <a...@irvine.com> wrote:
>>
>> > > On Mar 18, 8:54 am, Adam Beneschan <a...@irvine.com> wrote:
>>
>> > > > However, I tried changing the declaration of T as follows:
>>
>> > > >    T : String (1 .. B.L);  -- NO, THIS IS WRONG, I SCREWED UP
>>
>> > > > and GNAT accepted it.  (I haven't done enough testing to make sure
>> > > > GNAT handles it correctly in other ways, though.)  Here, B refers 
>> > > > to
>> > > > the "current instance" of the type (8.6(17)), and 3.7(18) means 
>> > > > that
>> > > > all instances of the type will have a component L that is inherited
>> > > > from A, so this should be legal unless there are some other rules 
>> > > > that
>> > > > I've missed (and that GNAT also missed).
>>
>> > > Never mind.  After reading Bob's post, I got pointed to 3.8(10-12),
>> > > which disallows references to inherited discriminants in a type
>> > > extension.  So I guess GNAT (or at least the version I'm using, which
>> > > is probably not the latest) is wrong to accept this.  Sorry.
>>
>> > >                                   -- Adam
>>
>> > --
>> > I tried Bob's answer with the Aonix compiler:
>> > ERROR : LRM:3.8(12), A discriminant used in a constraint may only
>> > appear alone as a direct_name.
>> > I'm lost...;-)
>>
>> 3.8(12) is one of the rules I overlooked (thanks, Tuck).  Perhaps you
>> tried  Bob's answer together with my incorrect suggestion to use
>> string(1..B.L), which violates that rule; when you use a discriminant
>> in a constraint, the discriminant can't be an "expanded name" or part
>> of a larger expression, and I think B.L is an expanded name here.  My
>> apologies for misleading you.
>>
>> This should work:
>>
>>     type B (L : Natural) is new A(L) with record
>>          T : String (1 .. L);
>>     end record;
>>
>> Everything I said earlier about visibility wouldn't apply here,
>> because redeclaring the discriminant L makes it visible inside the
>> record declaration of B.  This would work too:
>>
>>     type B (Ell : Natural) is new A(L) with record
>>          T : String (1 .. Ell);
>>     end record;
>>
>> It's the new discriminant that can be used in the declaration, not the
>> one inherited from A.
>>
>> > Is my first code correct? I guess yes...
>>
>> Still no.  The compiler may accept it, but that just means the
>> compiler has a bug.
>>
>> I hope I've got everything straight now.
>>
>>                                    -- Adam
> --
> You are right !!  , it works :-)
> Thanks for all.
> Tony.
> --

Tony,

Thanks for bringing this problem to our attention.

Tom Grosman, Aonix