Re: Recursive parameters in generics

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 23 Jul 2007 14:51:10 -0700, Adam Beneschan wrote:

> On Jul 23, 11:20 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
>> Hi there,
>>
>> out of curiosity, recently experimenting with workarounds for generics, I
>> invented a construct, which puzzles me. Is the following legal:
>>
>> generic
>>    S : String;
>> package A is
>>    S_Of : String renames S;
>> end A;
>> -----------------------------------
>> with A;
>> generic
>>    S : String;
>>    with package This_A is new A (S => S);
>> package B is
>> end B;
>> -----------------------------------
>> with A;
>> package My_A is new A (S => "whatever");
>> -----------------------------------
>> with My_A;
>> with B;
>> package My_B is
>>    new B (This_A => My_A, S => My_A.S_Of);
>> -----------------------------------
>> One could think that My_B would take S_Of from an instance of A and then
>> pass it back to A.
> 
> I don't see why this would be any different from
> 
> package My_B is new B (S => "whatever", This_A => My_A);

So you think it is legal?

> If you're thinking about My_B passing something back to A, you're
> probably thinking about the whole problem sideways.  My_B doesn't
> instantiate A at all, it uses an already-existing instance of A.

I mean the process of matching parameters. I.e. what happens at the
instantiation point. At least it perplexes GNAT, provided the thingy is
legal.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de