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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Empty Bounded Containers
Date: Fri, 23 May 2014 16:45:33 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:20036
Date: 2014-05-23T16:45:33-05:00
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<sbelmont700@gmail.com> wrote in message 
news:cfe5082c-9b50-4c5b-afe1-8dd6ea1640b9@googlegroups.com...
...
>which is not intuitively what I would assume.  For instance, the following 
>line:
>
>x : BC.Vector (Capacity => 42) := BC.Empty_Vector;

The problem here is using ":=" on bounded containers. Because of the 
capacity discriminant, it will never work quite right.

The whole reason that Assign and Copy were introduced into the Ada 2012 
containers is to work around this problem.

You want:
  X : BC.Vector (Capacity => 42) := Copy(BC.Empty_Vector, Capacity => 42);

Or:

   X : BC.Vector (Capacity => 42);

   BC.Assign (Target => X, Source => BC.Empty_Vector);

Ada has no way to avoid discriminant checks in ":=", so there is no 
possibility of making it work like you would want.

                                  Randy.