Re: In a pickle.

[Jim Rogers <jimmaureenrogers@worldnet.att.net>]

chris.danx wrote:

> Hi,
> 
> Is there a resolution to the following problem that allows convienant
> assignment of iterators?  An iterator points to a node in a list, like this
> 
>    -- Bi-Directional Iterator definition for positions within
>    -- objects of List_Type.
>    --
>    type Iterator_Type is new Ada.Finalization.Controlled
>    with record
>       List       :   List_Base_Access;
>       Position   :   Node_Access;
>    end record;
> 
> While more than one iterator points to a node it cannot be deallocated, with
> the number of iterators pointing to the node, recorded in the node itself.
> The problem is assignment!  If we do
> 
> Iterator := Next (Iterator);
> 
> The iterator is assigned to the next position, but the count of iterators
> isn't decremented so the node always thinks an iterator is on it.
> 
> I've just noticed something in Cohen that may help but am not sure if my
> interpretation is correct.
> 
> At the top of page 573 he says "The target variable in an assignment
> statement is finalized just before a new value is about to be copied to that
> variable".
> 
> Does this mean that in the above assignment Iterator is finalized after Next
> (Iterator) is evaluated but before the assignment takes place?  That would
> mean that a suitably coded finalize would do the job, correct?


That is my understanding of how assignment works.

Jim Rogers