Re: In precision typing we trust

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

On 2025-08-28 02:35, Lawrence D’Oliveiro wrote:
> On Thu, 28 Aug 2025 01:49:18 +0200, Dmitry A. Kazakov wrote:
> 
>> On 2025-08-28 01:10, Lawrence D’Oliveiro wrote:
>>
>>> So I can do something like
>>>
>>>       function F ... is declare
>>>          type T is ...
>>>       begin
>>>          ...
>>>          return T;
>>>       end;
>>>
>>> in Ada?
>>
>> No, you cannot spell such a function. Ada is a typed language:
> 
> But I thought you said “In Ada types can be created dynamically”? So it
> turns out that’s wrong? Because I can do that in Python.

You cannot refer to a type before you created it, except specific cases 
of incomplete declarations.

In Python you cannot do that either. What you can in Python is to 
declare a function that returns nobody knows what, because Python is 
untyped.

> So you can’t actually show us any example of such a feature, to prove it
> exists? Too bad ...

I can explain how it works. When a DLL is loaded its library level gets 
elaborated. So if you have:

package P is
    type T is tagged ...
end P;

in the main program or DLL and

with P;
package Q is
    type S is new T with ...
    function F return T'Class;
end Q;

in the DLL being loaded, then in the process of elaboration S will be 
created which in particular means extending of the dispatching table. 
You can return a class-wide object from there and dispatch on the newly 
created type's operation.

Clear?

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