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From: Victor Porton <porton@narod.ru>
Newsgroups: comp.lang.ada
Subject: Re: Both Ada.Finalization.Limited_Controlled and
 Ada.Finalization.Controlled
Date: Fri, 25 Jul 2014 22:25:24 +0300
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Date: 2014-07-25T22:25:24+03:00
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Victor Porton wrote:

> I have implemented the following package to wrap pointers to C records:
> 
> with Ada.Finalization;
> 
> generic
>    type Record_Type; -- It should be an untagged record for C
>    compatibility
> package RDF.Auxilary.Handled_Record is
> 
>    type Access_Type is access Record_Type
>       with Convention=>C;
> 
>    -- It is logically abstract, but not exactly abstract in Ada sense.
>    -- It can't be abstract because the function From_Handle returns this
>    type. type Base_Object is new Ada.Finalization.Limited_Controlled with
>    private;
> 
>    overriding procedure Initialize(Object: in out Base_Object);
> 
>    overriding procedure Finalize(Object: in out Base_Object);
> 
>    not overriding function Get_Handle(Object: Base_Object) return
>    Access_Type with Inline;
> 
>    not overriding function From_Handle(Handle: Access_Type) return
>    Base_Object with Inline;
> 
>    not overriding function Default_Handle(Object: Base_Object) return
>    Access_Type;
> 
>    not overriding procedure Finalize_Handle(Object: Base_Object; Handle:
>    Access_Type) is null;
> 
> private
> 
>    type Base_Object is new Ada.Finalization.Limited_Controlled with
>       record
>          Handle: Access_Type;
>       end record;
> 
> end RDF.Auxilary.Handled_Record;
> 
> I think you guess what the body is, but if you don't look into
> https://github.com/vporton/redland-bindings/blob/ada2012/ada/src/rdf-auxilary-handled_record.ads
> https://github.com/vporton/redland-bindings/blob/ada2012/ada/src/rdf-auxilary-handled_record.adb
> 
> Now I want to create a similar generic package with
> 
> type Base_Object is new Ada.Finalization.Controlled with private;
> 
> and a function to create a copy handle:
> 
> function Copy(Handle: Access_Type) return Access_Type is null;
> 
> and
> 
> procedure Adjust(Object : in out Base_Object) is
> begin
>    if Object.Handle /= null
>       Object.Handle = Copy (Object.Handle);
>    end if;
> end;
> 
> My question: Is it possible to implement without duplicating code for both
> Ada.Finalization.Limited_Controlled and Ada.Finalization.Controlled?

Oh, I thought one of .Finalization.Limited_Controlled and 
Ada.Finalization.Controlled is a child of another.

This is not the case, so the code should be duplicated (not a big problem in 
practice, however).

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