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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: orthogonal inheritance and extension aggregates
Date: Sat, 20 Jul 2013 00:49:41 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:igo2b70i4ox.t5duix9weguc$.dlg@40tude.net...
...
> P.S. I don't know if Ada 2012 silently inherits from null extension. I
> heard that there was an intention to add the kludge. Though semantically
> broken it would save programs like yours.

That's actually an Ada 2005 feature - see 3.9.3(4/2). One that I was against 
because it introduces a maintenance problem (null extensions tend to turn 
into non-null extensions over time, and once that happens, the feature stops 
working).

It appears that GNAT failed to properly implement this feature in the case 
described by the OP.

OTOH, as soon as the OP starts adding components to the extension, they'll 
have the problem again. (I don't think it is practical to extend the 
predefined containers, particularly because it's impossible to derive a 
cursor type to go with the extended container -- so you either end up with 
broken typing or you have do everything twice. And there are a lot of 
functions that have to be overridden.)

             Randy.