Re: What is the difference of "with null record" and "with private"?

[Victor Porton <porton@narod.ru>]

Shark8 wrote:

> On 23-May-14 12:19, Victor Porton wrote:
>> What is the difference of "with null record" and "with private"?
>>
>> Both denote a descendant of a type with no new additional public fields.
> 
> Incorrect.
> Null record does what you indicate, with private means that any fields
> aren't visible/public. Example:

I've said "no new additional PUBLIC fields" not just "no new additional 
fields"!

> Package Example is
>      Type Parent is tagged record
>          Data_1 : Integer;
>      end record;
> 
>      -- Returns Data_1
>      Function Get_Data (Item : Parent) return Integer;
> 
>      -- Contains Data_2, but this field is private.
>      Type Child is new Parent with private;
> 
>      -- Returns Data_2
>      Function Get_Data (Item : Child) return Integer;
> 
> 
> private
>      Type Child is new Parent with record
>          Data_2 : Integer;
>      end record;
> 
>      Function Get_Data (Item : Parent) return Integer is (Item.Data_1);
>      Function Get_Data (Item : Child)  return Integer is (Item.Data_2);
> 
> End Example;

-- 
Victor Porton - http://portonvictor.org