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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: 'Protected' abstract subprograms
Date: Wed, 15 Jan 2014 17:17:46 -0600
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2014-01-15T17:17:46-06:00
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"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wcck3e18he0.fsf@shell01.TheWorld.com...
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
...
>> Just one trivial example of slack privacy. You cannot hide default 
>> values:
>>
>>    type T is private;
>
> If you have:
>
>    function V return T;
>
> then the default value is hidden.

Or of course you can use a deferred constant, again the value isn't visible.

    V : constant T;

It's mildly unfortunate that this latter and the former aren't semantically 
equivalent (they should be), but that doesn't have much to do with the 
point.

Dmitry might be wanting to hide the *name* of the value, but that's a silly 
thing to do. Most of the time, people want *more* access to these things, 
not less. If we did provide a way to hide the name of the value, we'd also 
have to provide a way to get the name without using the name:
   Foo.X'Default
Which is just a lot more complex way of making that name visible in your 
interface. All it would do is add a lot more language complexity.

(This problem has come up repeatedly in Ada; the most recent one is a 
request to access the Default_Value for a type; there is no such mechanism 
in Ada 2012, in large part because what the value ought to be for a type 
that doesn't have Default_Value specified is uncertain.)

Ada might have cases of "slack privacy", but I don't think this is one of 
them.

                         Randy.