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Date: Wed, 06 Aug 2014 06:50:17 +0200
From: Per Sandberg <per.s.sandberg@bahnhof.se>
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Newsgroups: comp.lang.ada
Subject: Re: A bad counterintuitive behaviour of Ada about OO
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Date: 2014-08-06T06:50:17+02:00
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The program is doing exat what is should.
May i sugest you to put the folowing line in all methods.
---------------------------------------------------------------------
pragma debug (GNAT.IO.Put_Line (GNAT.Source_Info.Enclosing_Entity & " " 
& Object.Handle'img));
--------------------------------------------------------------------
And compile with assertions enabled.
And reflect on the output.

/Per

On 05.08.2014 22:09, Victor Porton wrote:
> http://freesoft.portonvictor.org/binaries/ada-obj-test.tar.gz
>
> contains a tiny Ada program which prints 0 despite intuition suggests that
> it should print 123, because it just copies (using Adjust) an object holding
> 123.
>
> In this program Handle_Type models some handle provided by an external API,
> where 0 is an undefined handle. Base_Object is a tagged record which holds a
> handle inside itself and can copy or destroy the handle automatically (as
> Base_Object is a controlled object).
>
> Example_Record is a derived type of Base_Object which imitates a behavior of
> a simple library which operates over some handles. For example, in this
> example copying a handle preserves it unchanged.
>
> This tiny program was created by me as a model of my real Ada bindings for
> Raptor C library, which produces a wrong behavior.
>
> Why Ada behaves in this counter-intuitive way?
>
> What should I do in similar situations when developing real Ada software?
>