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From: "Martin Dowie" <martin.dowie@baesystems.com>
Newsgroups: comp.lang.ada
References: <43CCAB76.6050907@mailinator.com>
Subject: Re: Ada 2005 box (<>) rules in default values
Date: Tue, 17 Jan 2006 09:35:01 -0000
Organization: BAE SYSTEMS
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Date: 2006-01-17T09:35:01+00:00
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Alex R. Mosteo wrote:
> Hi all,
[snip]
> with this will also be welcome).

Your understanding seems to be what John Barnes describes in his paper at
"http://www.gnat.com/ada_2005.php#":

"The main change is that the box notation <> is now permitted as the value
in a named aggregate. The meaning is that the component of the aggregate
takes the default value if there is one.
So if we have a record type such as

type RT is record A: Integer := 7; B: access Integer; C: Float; end record;

then if we write

X: RT := (A => <>, B => <>, C => <>);

then X.A has the value 7, X.B has the value null and X.C is undefined. So
the default value is that given in the record type declaration or, in the
absence of such an explicit default value, it is the default value for the
type. If there is no explicit default value and the type does not have one
either then the value is simply undefined as usual.

The above example could be abbreviated to

X: RT := (others => <>); "