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Date: Wed, 13 Feb 2019 09:40:21 -0800 (PST)
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Subject: Mixing public and private member of a class. Dealing with what to
 hide and not
From: Daniel Norber <danielnorberto@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:55508
Date: 2019-02-13T09:40:21-08:00
List-Id: <comp.lang.ada>

Sorry for my bad english.
I'm having big troubles in how Ada deals mixing public and private member o=
f a class.=20

Please someone can help how to do it using Ada ?

Im building lets say a library, where i choose to use classes (tagged types=
) for interfacing with the outer world.

This library is organized in services using ada packages.

Lets say my Library is called SERVICES and it has differents parts, for exa=
mple massaging service and making pizzas service. Every services goes in a =
differente child package, but i will focus just in massaging service packag=
e.

I had two approaches. One trying to build classes in the same package and i=
 always get "premature=20
derivation of derived or private type", so i will explain how i try using d=
ifferents tagged in different packages paradigm.

As i understood, the only way to mix public and private members is declarin=
g the public part and make a child with private;

Here is my code:

package SERVICES is
pragma PURE;
end SERVICES;

-having 1 dependency with my internal code:
with REGISTERING_STUFF;
package SERVICES.MASSAGES is
   type dont_instance_me_bcs_im_not_full_but_public is record
       Register : REGISTERING_STUFF.notebook;
   end record

   type instance_bcs_im_the_good is new dont_instance_me_bcs_im_not_full_bu=
t_public with private;

   --public part for the outer world:
   procedure makeme_a_massage_in_public (S: instance_bcs_im_the_good);
   function Say_in_public_if_its_painfull(S:instance_bcs_im_the_good) retur=
n boolean;

private

   --private part for my massaging related code
   type instance_me_bcs_im_the_good is new dont_instance_me_bcs_im_not_full=
  with record
      more_secret_data  : natural;
   end record;
   procedure changemysecrets (S: instance_me_bcs_im_the_good);
end SERVICES.MASSAGES;


package REGISTERING_STUFF is
   type notebook is tagged limited private;
   function whoami (S: notebook) return String;

private

   type notebook is tagged record
      private_secret_data : natural;
   end record;
   procedure takecarechangingnotes (S: notebook ;data: String);=20
end REGISTERING_STUFF;


So from a client to the library, i try this:


--The client only Have 1 dependency with my library
with SERVICES.MASSAGES;

package client body is

  interface_class : SERVICES.MASSAGES.instance_me_bcs_im_the_good;

begin

  ada.text_io.Put_Line(interface_class.Register.whoami);

end client;


I have the next error running client:
>error  no selector whoami for private type notebook


I want one and simple class that includes everything to the outer world lik=
e "instance_me_bcs_im_the_good" that expose the public part like procedure =
"makeme_a_massage_in_public", and also the public part of "notebook" like "=
whoami" function, but hidding for example takecarechangingnotes just for in=
ternal use . In the same way this whole class has private parts like "chang=
emysecrets" not available for the outer world.

Any help or ideas of how to do it? (if it possible respecting 1 "with" depe=
ndency in the outter world side)

Thank you very much and Best regards.