Re: Task components, the rationale

["Randy Brukardt" <randy@rrsoftware.com>]

"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message 
news:a30f4a5d-baee-40b5-b30d-2a15042868e7@r9g2000yql.googlegroups.com...
...
>If you ask me from the top of my head how *exactly* this can be
>solved, I will not attempt to give a full solution (hey, the committee
>has a full decade for it ;-) ),

Well, actually, work on Ada 2020 would need to be finished by late 2018 in 
order to have a good chance of being standardized in 2020. Since it is 
mid-2011 now, I think that is more like 7 years than 10.

...
> but one of the possible ideas might
>involve adding a lifetime information to the access discriminant, just
>as it is done for tracking scopes of types and objects with anonymous
>access parameters today.

That was suggested for Ada 2012 [by me and others], and it turns out that it 
cannot be done (at least with the sorts of lifetime indications that Ada has 
used to date). If it was mandated, it would necessarily make Ada 
implementations far more expensive than they currently are -- so I doubt 
very much that we'll see that. (Sorry, I don't remember which AI we were 
discussing at the time, so I can't give you a reference.)

The static accessibility model for access discriminants is *very* 
problematical; it leads to distributed overhead for functions that might 
return something with a discriminant -- yet that still is considered 
preferable to any dynamic model.  My preference is to not use them at all 
(not always possible, as shown by some of these examples).

                                      Randy.


                              Randy.