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From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: Is T an ancestor of T?
Date: Fri, 15 Oct 2004 17:19:22 +0000 (UTC)
Organization: GMUGHDU
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Date: 2004-10-15T17:19:22+00:00
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Martin Krischik <krischik@users.sourceforge.net> wrote:
: Georg Bauhaus wrote:
: 
:> Martin Krischik <krischik@users.sourceforge.net> wrote:
:>  
:> :> 'class as return type of constructor functions creates a number of
:> :> not-so-nice conversion necessities that I'd like to avoid.
:> : 
:> : I thought as an example. Not to actually use this constructor pattern.
:> 
:> Interestingly, GNAT complains if T is derived from some other
:> type Base. For example,
:> 
:>       function Make return T'Class is
:>       begin
:>          return T'(T with N => 42);
:>       end Make;
:> 
:> 
:>      7.          return T'(T with N => 42);
:>                            |
:>         >>> expect ancestor type of "T"
:> 
:> (Same for specific T.)
: 
: Well T is not an ancestor of T.

Not in this example where it is derived from another type, named Base.

: T is T itself. You might want try the
: example with a tagged type which actually has a parent to see the
: difference.

This is exactly what I have been doing, the results above are
for a T that is derived from another type, named Base.
In this GNAT spits out this error message. Otherwise it doesn't.

I still don't know whether or not a type is an ancestor of itself,
given that it is a descendant of itself.


-- Georg