Re: little precision about anonymous access types

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

On 17/05/2018 23:17, Randy Brukardt wrote:
> "Mehdi Saada" <00120260a@gmail.com> wrote in message
> news:d294e4a5-864c-4ab0-bf60-6c9a94ace651@googlegroups.com...
>> So if it was you, you would have treated subprograms with
>> access types parameters as primitives, as long as they are declared
>> in the same immediate scope ? It sounds simple, why hasn't it be
>> do that way ?
> 
> No, I wouldn't bother with dispatching on access values at all. Since Ada
> passes all tagged objects by reference, and 'Unchecked_Access is always
> allowed on tagged parameters, it's always possible to get an access to a
> tagged parameter if that is needed. There's no reason to *pass* that value -
> just pass the tagged object.

You forgot the return. Return by reference was killed and there is no 
substitute for

    function Foo return access T;

> Essentially, there's no implementation difference (ignoring the abomination
> of dynamic accessibility) between "access T" and "in out T" for a tagged
> type T.

Yes, but there must be difference if the type system were fixed to allow 
classes of non-tagged and by-value objects.

I agree that controlling access T could be made superfluous by carefully 
designed references.

I also believe that having an operation for T and not having it for 
access T and conversely is not good. I.e. if there is

    procedure Foo (X : in out T);

then that must automatically define

    procedure Foo (X : access T);

and conversely. Rules for automatic dereferencing do this in some cases.

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