Re: [HELP] Why is 'Adjust' not called here ???

["Pat Rogers" <progers@classwide.com>]

"Didier Pieroux" <dpieroux@pi.be> wrote in message
news:3C5FB880.6FD36A12@hotmail.com...
> Hello,
>
> To make it short: why is 'Adjust' not called during initialization by a
> aggregate ?
>
> I give an example below illustrating my question.  'A.Instance' is a
> controlled type with Initialize, Adjust and Finalize redefined to print
> their name.
>
> I thought that the elaboration of
>
>    Item1 : A.Instance := (Ada.Finalization.Controlled with 10);
>
> would call the 'A.Adjust' procedure... It is not the case. However,
> 'A.Adjust' is called as expected after the elaboration of
>
>    Item2 : A.Instance := Item1;

It is because the first case is initialization via an aggregate, but the second
case (immediately above) is not via an aggregate.


> I check that behavior with both the Gnat and Aonix compiler.  So, I am
> clearly missing something here, and I can't find the answer in my books
> (Barnes, Cohen, Ben-Ari and the RM)
>
> Also, could someone
> - Explain me the rational for not calling 'Adjust' in the first case ?

See below.

> - Give me the key reference(s) in the RM from which this behavior can be
> deduced ?

RM 7.6 {17.1/1}  {For an aggregate of a controlled type whose value is assigned,
other
than by an assignment_statement or a return_statement, the implementation
shall not create a separate anonymous object for the aggregate. The aggregate
value shall be constructed directly in the target of the assignment operation
and Adjust is not called on the target object.}

17.h.1/1 Reason: This is necessary to prevent elaboration problems with deferred
constants of controlled types. Consider:

package P is
   type Dyn_String is private;
   Null_String : constant Dyn_String;
   ...
private
   type Dyn_String is new Ada.Finalization.Controlled with ...
   procedure Finalize(X : in out Dyn_String);
   procedure Adjust(X : in out Dyn_String);

   Null_String : constant Dyn_String :=
      (Ada.Finalization.Controlled with ...);
   ...
end P;

17.h.3/1 When Null_String is elaborated, the bodies of Finalize and Adjust
clearly have not been elaborated. Without this rule, this declaration would
necessarily raise Program_Error (unless the permissions given below are used by
the compiler).


---
Patrick Rogers                       Consulting and Training in:
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