Re: New aggregates with Ada 2022.

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:t8ujnr$1hvf$1@gioia.aioe.org...
> On 2022-06-22 01:39, Randy Brukardt wrote:
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>> news:t8qrmo$p79$1@gioia.aioe.org...
>> ...
>>> 1. Built-in operations -> hiding:
>>>
>>>     type T is private;
>>>     function "+" (Left, Right : T) return T; -- Perfectly legal
>>> private
>>>     type T is range 1..100;
>>>
>>> 2. Primitive operations -> overriding.
>>
>> BTW, these two are really the same thing. In the first example, the "+" 
>> is
>> overriding the predefined operation.
>
> Yes, they should be in a better world. A primitive operation is always 
> reachable. The case above works differently from:
>
>    type T is private;
>    overriding
>    function "+" (Left, Right : T) return T is abstract;
>
> But this is a deeper problem of having such operations primitive.
>
>> But note an important difference here from the aggregate case: in no case 
>> is
>> an operation available for the private type that is *not* available for 
>> the
>> full view. Since the syntax and semantics of container aggregates and 
>> array
>> aggregate are subtly different (they are as close as we could make them, 
>> but
>> that is not that close), there definitely are things that would be only
>> possible when written for the private view. That would be new for Ada. So
>> while a definition could be made, it would be confusing in some cases. 
>> And
>> this case isn't useful enough to make that effort.
>
> Much could be resolved by attributing proper types to all assumed or real 
> intermediate steps:
>
>    type T is private;
>    function "+" (Left, Right : T) return T;
> private
>    type T_Parent is range 1..100;
>    type T is new T_Parent;

Don't think this changes anything (at least not in Ada as it stands), since 
that is essentially the meaning of "range 1 .. 100":

     type Some_Int is range 1 .. 100;

means

    type Some_Int is new <Some_Int_Chosen_by_the_Impl> range 1 .. 100;

                        Randy.