Re: Self pointer in limited record

["Jeffrey R. Carter" <spam.jrcarter.not@acm.nospam.org>]

amado.alves@gmail.com wrote:
> 
> type T is -- limited or not
>    Self : access T := T'Unchecked_Access;
>    ...
> end;
> 
> But the compiler will remind you that Unchecked_Access is not
> available for types.
> (It seems Ada is like most women: unnecessarily complicated and
> difficult :-)

What I have had occasion to use successfully is

type R;

task type TT (Parent : access R);

type R is new Ada.Finalization.Limited_Controlled with record
    T : TT (Parent => R'access);
    ...
end record;

V : R;

V.T.Parent designates V.

Some points for this idiom:

R must be limited, because it contains a limited component (the task).

"The current instance of a limited tagged type, a protected type, a task 
type, or a type that has the reserved word limited in its full 
definition is also defined to be aliased." (ARM 3.10). This sort of 
thing may not work if R is not one of these cases (and so the current 
instance referred to by R in R'access is aliased); I haven't tried it.

I usually have done this when revising others' existing code; there 
generally seem better designs when starting from scratch.

-- 
Jeff Carter
"Apart from the sanitation, the medicine, education, wine,
public order, irrigation, roads, the fresh water system,
and public health, what have the Romans ever done for us?"
Monty Python's Life of Brian
80