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Date: Fri, 23 May 2014 22:45:36 +0200
From: Georg Bauhaus <rm-host.bauhaus@maps.futureapps.de>
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Subject: Re: What is the difference of "with null record" and "with private"?
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Date: 2014-05-23T22:45:36+02:00
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On 23/05/14 20:55, mockturtle wrote:
> Well, as I see it, it is more a matter of visibility.

"with private" acts pleasantly strong WRT visibility,
in a technical sense, even "locally". Leaving out nested
packages, still some of the types below must be rejected
by the compiler:

package Privacy is

    type T0 is tagged private;
    type T  is tagged null record;

    type T1  is new T0 with private;
    type T1n is new T0 with null record;

    type Np  is new T  with private;
    type N   is new T  with null record;
    type Np0 is new T0 with private;
    type N0  is new T0 with null record;

private
    type T0  is tagged null record;

    type T1  is new T0 with null record;
    type Np  is new T  with null record;
    type Np0 is new T0 with null record;
end Privacy;

All of these have to do with when a type's definition
is finished, and the combination of placement and
privacy control will affect later derivations, too.