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From: porton@ex-code.com (Victor Porton)
Date: Mon, 13 Jan 2003 16:28:53 +0500
References: <mailman.1042446542.5578.comp.lang.ada@ada.eu.org>
Organization: Extreme Code Software (http://ex-code.com)
Subject: Re: Finalization of tagged types - problem
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In article <mailman.1042446542.5578.comp.lang.ada@ada.eu.org>,
	"Grein, Christoph" <christoph.grein@eurocopter.com> writes:
> From: porton@ex-code.com (Victor Porton)
> 
>> I have a non-limited tagged type (not derived from
>> Ada.Finalization.Controlled) Base.
>> 
>> I derive:
>> 
>> type State_Type is new Base with
>>    record
>>       -- ...
>>       Finalizer: Finalizer_Type(State_Type'Access);
>>    end record;
>> 
>> I want to add a component with back-reference derived
>> from Ada.Finalization.Controlled or
>> Ada.Finalization.Limited_Controlled for auto-finalization
>> of State_Type.
>> 
>> But
>> 
>> type Finalizer_Type(State: access State_Type) is
>>    new Ada.Finalization.Controlled with null record;
>>    
>> Compiler: "Access discriminant are allowed only for limited types".
>> 
>> Can be done something among the obvious but imperfect
>> solutions: 1. make Base controlled. 2. make Base limited
>> and derive Finalizer_Type from Limited_Controlled instead?
> 
> I've published a few years ago in Ada Letters a paper "Add Finalization" dealing 
> with this problem. You can find it online on my home page
> 
> <http://home.T-Online.de/home/Christ-Usch.Grein/Ada/Finalization.html>

Christoph, thanks.

So is it your opinion: derive from Controlled if it may be needed
in a derived?

BTW, Is derivance from Controlled a big overhead?