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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Unchecked deallocation question
Date: Fri, 26 Nov 2004 10:06:25 +0100
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Date: 2004-11-26T10:06:25+01:00
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On Fri, 26 Nov 2004 00:24:15 +0100, Adrien Plisson wrote:

> Martin Krischik wrote:
>> You should carefully thing if you really need it. Unlike C/C++ the following
>> is actually valid:
>> 
>> declare
>>     It : Root'Class := Derived'(...);
>> begin
>>     ...
>> end;
> 
> mmmm, i don't think there is any problem doing this in C++:
> 
> class Root;
> class Derived : public Root;
> 
> Root &It = Derived( ... );
> 
> it just uses a reference type which is almost the same as ada access 
> type but you cannot assign null to it and cannot dereference it.

Right, the difference appears when Derived is created by a factory:

declare
   It : Root'Class := Create (...);
begin

Here Create returns Root'Class, so the actual type is unknown until
run-time. In C++ this is only possible using heap and pointers. In Ada It
will be indeed allocated on the stack.

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