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From: Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid>
Newsgroups: comp.lang.ada
Subject: Re: In precision typing we trust
Date: Wed, 27 Aug 2025 23:10:31 -0000 (UTC)
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On Wed, 27 Aug 2025 09:39:59 +0200, Dmitry A. Kazakov wrote:

> On 2025-08-27 02:13, Lawrence D’Oliveiro wrote:
>>
>> On Tue, 26 Aug 2025 09:59:48 +0200, Dmitry A. Kazakov wrote:
>> 
>>> On 2025-08-25 23:13, Lawrence D’Oliveiro wrote:
>>>>
>>>> On Mon, 25 Aug 2025 22:09:14 +0200, Dmitry A. Kazakov wrote:
>>>>
>>>>> The question remains why should I need to instantiate it beyond
>>>>> declaring an object of?
>>>>
>>>> Because in Python a class, like all objects, is created at runtime,
>>>> not compile time.
> 
> Not true, because in Python there exist types created before the
> interpreter starts.

No. Builtins are created as part of interpreter startup, not before. Prove 
me wrong.

> In Ada types can be created dynamically:
> 
>     declare
>        type T is ...
>     begin
>        ...
>     end;
> 
> The difference is that the semantics of such types is static in Ada and
> undefined in Python.

Please show us Python code demonstrating how they are “undefined in 
Python”.

>> No. In Ada, C or C++, definitions are not “executable”. They do not
>> “create objects”.
> 
> Of course they are executable.

So I can do something like

    function F ... is
    declare
       type T is ...
    begin
       ...
       return T;
    end;

in Ada?

>> Think of a function that is a class factory: each time it is called, it
>> creates and returns a new class as the function result. This depends
>> crucially on a) classes as first-class objects, and also b) lexical
>> binding.
>> 
>> Can you do that in Ada, C or C++? No you cannot.
> 
> Yes I can. It is actively used in software design. E.g. for plug-ins,
> library implementing a driver derives  a type from the base type.

Show us.