Re: Put the access value

[ldries46 <bertus.dries@planet.nl>]

Op 14-4-2020 om 13:05 schreef Jeffrey R. Carter:
> On 4/14/20 9:15 AM, ldries46 wrote:
>>
>> type Buffer_Pointer is limited private;
>>
>>     type Block_Buffer is record
>>        nr       : integer;
>>        buf      : Item;
>>        previous : Buffer_Pointer := null;
>>        next     : Buffer_Pointer := null;
>>     end record;
>>
>>        El  : Buffer_Pointer := LastBuffer;
>>        El1 : Buffer_Pointer;
>>
>> I just want to see if the routing of thedifferent Buffer_Pointer's is 
>> correct so I thought Buffer_Pointer'Image(El) would show the value of 
>> The Pointer El f.i. ?x000000 for null or even the simpel decimal 
>> value 0.
>
> 1. There are no access types in this code. The declaration of type 
> Block_Buffer is invalid because null cannot be a valid visible value 
> of type Buffer_Pointer
>
> II. Assuming the full type of Buffer_Pointer is an access type, and 
> the declaration of Block_Buffer can see the full type, it appears you 
> are creating a linked list. Why not use 
> Ada.Containers.Doubly_Linked_Lists?
>
> C. Assuming you're still going to use access types, why are you 
> interested in the internal representation of access values? These will 
> probably appear to be random values that provide no information, 
> except perhaps whether the value is null
>
> iv. If you're only interested in whether an access value is null or 
> not, this can be better determined without showing the internal 
> representation:
>
> "El is null " & Boolean'Image (El = null)
>
> "El is " & (if El = null then "" else "not ") & "null"
>
Thanks to mr J.P Rosen this worked
and I have checked a Buffer random Buffer insert routinethat looked like 
it didn't work but I could see that it in fact worked correctly. I used 
the Ada Unchecked conversion.

Mr Carter the Buffer_Pointer is an access  declaration which was limited 
private. And I just had presented it for the possibility that the 
problem should be created by its limited private pro