Re: In precision typing we trust

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

On 2025-08-24 23:50, Lawrence D’Oliveiro wrote:
> On Sun, 24 Aug 2025 10:37:53 +0200, Dmitry A. Kazakov wrote:
> 
>> Well, I maintain Ada Python bindings. When I looked at Python "derived"
>> types in its API, I was astounded by a total lack of inheritance.
> 
> Don’t know what you mean.

https://docs.python.org/3/c-api/type.html

PyType_FromSpec etc.

> Python not only has inheritance, it has full
> multiple inheritance with C3 linearization.

No members are inherited. E.g. in Ada

type T is tagged record
    M : Integer;
end record;

type S is new T with record -- S is derived from T
    N : Float;
end record;

declare
    X : S;
begin
    X.M := 1; -- M is inherited

https://stackoverflow.com/questions/10064688/cant-access-parent-member-variable-in-python

Not to say that nothing is checked etc. Expecting that from an untyped 
language would be silly anyway.

But in OO it is incorrect to inherit covariant methods with arguments in 
the out or in-out mode, for example methods returning the type from the 
class:

function Covariant return T;

This would be broken for obvious reasons. So in a properly typed OO 
language, like Ada, you will be required to override Covariant upon 
derivation from T:

overriding
    function Covariant return S;

> It also has metaclasses.
> Because classes, like functions, are first-class objects.

A useless thing in an untyped language and in general one should first 
question what could be the purpose of a set of a set of types? Provided 
one could implement that thing (let's ignore pitiful Python), What 
algorithmic problems one could solve with that?

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