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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: I'm facing an issue with: call to abstract procedure must be
 dispatching
Date: Tue, 8 Dec 2015 18:42:04 +0100
Organization: cbb software GmbH
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Date: 2015-12-08T18:42:04+01:00
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On Tue, 8 Dec 2015 09:24:58 -0800 (PST), Serge Robyns wrote:

> On Tuesday, 8 December 2015 18:05:09 UTC+1, Dmitry A. Kazakov  wrote:
> 
>>    The_Store : aliased T_Store;
>>    Client : T_Client;
>> begin
>>    The_Store.Insert  (Client);
> 
> Yes, I know this does work.  I did compile the example first like that.
>  But this is an attempt to "simplify" the problem to post it here.  What
> really happens is the following.
> 
> In the main package I'm actually calling other packages passing the
> The_Store. For example:
> 
> -- with Store.Gnatcoll_version;
> with Store.Inmemory_Container_version;
> 
> Both implement the same interface but with different underlying storage.
> In the case of in_memory, I'll keep containers inside the type T_Data_Store
> and in case of Gnatcoll some DB parameters inside T_Data_Store
> and then ...
> 
>    Do_Something (The_Store);
> 
> The signature of Do_Something is
>    procedure Do_Something (A_Store : in out T_Abstract_Store);

In which relation is Do_Something to T_Abstract_Store?

1. a primitive operation =
      has a separate implementation for each concrete type (from the class)
2. class-wide operation =
      has same implementation for all types (from the class)

(anything else is a design fault)

> Inside that procedure I'm using the A_Store. This regardless how A_Store
> got implemented.

That sounds like #2. Then it must be declared as:

procedure Do_Something (A_Store : in out T_Abstract_Store'Class);

> However all "users" will just call "A_Store.Insert (Something);" or
> "Something := A_Store.Get (ID);", etc.

You lost me here. What has this to do with Do_Something?

> If I've to use the "real" instance, I've to edit all packages that
> "with"'s depending on the case.  In some languages this could controlled
> by a pre-processor directive.  Any other suggestion?

I don't understand the problem. You are trying to explain a [failed]
solution of some problem. I would suggest you to start with the problem.

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