Re: Ada design bug or GNAT bug?

[Shark8 <onewingedshark@gmail.com>]

On Thursday, July 2, 2015 at 6:04:50 PM UTC-6, Randy Brukardt wrote:
> 
> The reason Ada has anonymous access parameters was a desire (for Ada 9x) 
> that code from existing OOP languages like C++ could be directly converted 
> to Ada without having to think at all (thinking being necessary to get rid 
> of access types).

Do you think, in hindsight that (anonymous access parameters) was a mistake?

> [snip]
> >
> >One may think that the distinction between class type and tagged type is 
> >subtle, but the
> >implications of it are huge : without class object one needs as replacement 
> >access to a
> >class wide type. This has led to the use of access values everywhere when 
> >doing OOP.
> >To ease the pain access parameters and anonymous access types were 
> >introduced...
> 
> This seems to me to be nonsense. There's no need to use access types in Ada 
> OOP interfaces; "in out T" and "access T" have virtually the same semantics 
> when T is a tagged type. (Claw only has one access type in its entire 
> interface, used for a return type that ought to be by reference. Everything 
> else does not use visible access types.) It's more work this way, but it's 
> definitely possible.

I think I remember getting an error-message in GNAT awhile back about return and reference semantics... wasn't that something that Ada95 had but was later forbidden in Ada 2005? -- Also, do you think it would have been better to have extended-return signal to the compiler a desire for a build-in-place return-object?

Also, I seem to recall your dislike of INTERFACEs -- in hindsight, what would you have done differently if you needed the mechanism of "Type T has functions X, Y, and X" applied to a group of types? Generics, or some variations thereof?

>> with P1; use P1;
>> package P2 is
>>   type T3 is new T1 with private;
>> private
>>   type T3 is new T2 with null record; -- Legal!
>
>This is only legal because of a hack, which I was very much against
introducing. If you have an extension component, this is illegal:
>
>    type T4 is new T2 with record C : Character := '1'; end record; --  
Illegal!!!

Why is this hack required?/How was it justified? How would you address the problem w/o resorting to this hack?


Other than those specifics, I'm quite interested to know what you regard to be mistakes in Ada's design.