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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Lower bounds of Strings
Date: Tue, 12 Jan 2021 10:37:41 +0100
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On 2021-01-12 09:19, Randy Brukardt wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:rtc1vu$1cfj$1@gioia.aioe.org...
> ...
>> Of course it will simplify everything. E.g. our beloved generics. Compare
>>
>>     generic
>>        type I is (<>);
>>        type E is private;
>>        type A is array (I range <>) of E;
>>
>> with
>>
>>     generic
>>        type A is new Root_Array_Type with private;
> 
> Surely, it simplifies it to uselessness. You haven't declared the index and
> component types here.

It is a different issue, same like T and T'Class. You can get T'Class 
type from T. So there should be A'Index and A'Element type-valued 
attributes to get the companion types. In the traditional syntax:

    generic
       type A is array (<>) of <>;
    package Foo is
       subtype I is A'Index;
       subtype E is A'Element;

> And if they are implicit in Root_Array_Type, you've
> now run into the fundemental problem of interfaces: you need a generic or
> everything has to be related in order to use an interface.

Not fundamental, we just need Ada 83 "new" back:

    type S is new new T with private;
       -- Ada 83 new on top of Ada 95 new (:-))

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