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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: tagged type as generic parameter
Newsgroups: comp.lang.ada
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Date: Fri, 4 Jan 2008 15:17:10 +0100
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Date: 2008-01-04T15:17:09+01:00
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On Fri, 04 Jan 2008 14:08:52 +0100, Philippe Tarroux wrote:

> Dmitry A. Kazakov a �crit :

>> The function A_Data returns Data. It is a primitive operation of Data and
>> thus covariant in the result. So when you derive anything from Data, you
>> have to override it in order to provide a correct implementation that would
>> return the derived type rather than the base.
>>   
> Ok. But does it mean that only the constructor is a primitive operation 
> of the data type, not the print procedure? In this case why Print 
> doesn't need to be redefined?

Right, the reason why Print need not to be overridden is that it has Data
passed in the in-mode. So the caller has Data already constructed
elsewhere. For the same reason a procedure with an in-out-mode parameter
can be safely inherited too. Considering strictly out-mode parameters, it
could be otherwise, in general case. But in Ada tagged types have to be
constrained and constructed even when they are outs.

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