Re: Experimenting with the OOP features in Ada

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2017-01-05 12:41, Laurent wrote:
> On Wednesday, 4 January 2017 13:44:31 UTC+1, Dmitry A. Kazakov  wrote:

>> Object.Entity and Object.Archived.Deposit are already tagged.
>>
>>>
> And that is why there is no place to put it? Or does abstract automatically
> implies tagged?

No.

Object.Entity is derived from Ada.Finalization.Limited_Controlled which 
is tagged.

[Tagged property is transitive upon derivation.]

>> The package name Object gets hidden by the declaration the type Object.
>> Change it to:
>>
>>    type Object is abstract new Standard.Object.Entity ...
>>
> Why Standard? Thought that was for libraries which come preinstalled? I thought I
> get access to Simple Components via Gnoga?

Standard is the root package in Ada. So the full name of the package 
Object is Standard.Object.

> So previous errors are gone, a new one:
>
> base_types-antibiotics.ads:30:9: type must be declared abstract or "Get_Class"
> overridden
>
> So I looked at Get_Class.
>
> -- Get_Class -- Of an object
> --
> --    Object - The object
> --
> -- This  function  returns  the  class  of Object. The class is a string
> -- uniquely  describing  the  object's type. It is analogous to external
> -- type  tag representation. Though, different types of objects may have
> -- same class if necessary.
> --
> -- Returns :
> --
> --    The object class
> --
>    function Get_Class (Object : Deposit) return String is abstract;
>
> Hm is abstract, so no body to copy from. What is it doing?

A persistent object must be stored externally. When you restore it you 
must know its Ada type. The string returned by Get_Class is the 
information you will use to get at that type.

> If Object is of type ie.: Base_Type it will return a String with Base_Type?

It is any text. See 2.4 and 2.4.2 for sample code. 2.4.2 implements a 
persistent binary tree of nodes. Each tree node is a separate persistent 
object.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de