Re: Generic access type convention and aliasing

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Tue, 07 May 2013 23:03:17 +0200, Jacob Sparre Andersen news  
<randy@rrsoftware.com> a écrit:
>>       A3 : General_Access := S.Element; -- And the same.
>    Yes, of course this is legal, but it also includes a dynamic
> accessibility check which will fail for this example. (S.Element is much
> shorter lives than type General_Access). So it will raise Program_Error.

Right, but I badly wish static check/static failure (may be I want too  
much, I believe Ada should have this with the hot area of access value).

> Moreover, the use of access parameters and SAOAATs should be avoided

What is “SAOAATs”?

> unless
> you really need dynamic accessibility.

What I'm trying to achieve, is to have access to the object storage  
designated by the access, while preventing manipulation (including copying  
at any life‑time scope) of this access value, only dereference. The only  
way I know to achieve this, is by passing `Element.all` to an  
out/in‑out/in parameter of a callback, but I would like to avoid control  
inversion (this breaks the flow).

I feel there is no way to solve it or I want too much, and I should stop  
searching and go with the storage specific access discriminant (so no  
implicit dereference), and use some kind of external static check. At  
least storage specific access type offers a tiny bit more protection than  
general access, being a discriminant it can't be modified, and being an  
access value, use of a not allocated or deallocated element will be always  
caught at runtime, even with check disabled… the most I can get, so I will  
go with it.


-- 
“Syntactic sugar causes cancer of the semi-colons.” [1]
“Structured Programming supports the law of the excluded muddle.” [1]
[1]: Epigrams on Programming — Alan J. — P. Yale University