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From: "Alex R. Mosteo" <devnull@mailinator.com>
Newsgroups: comp.lang.ada
Subject: Re: private types
Date: Tue, 14 Mar 2006 09:47:10 +0100
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Date: 2006-03-14T09:47:10+01:00
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Brian May wrote:
>>>>>>"Jeffrey" == Jeffrey R Carter <spam.not.jrcarter@acm.not.spam.org> writes:
> 
>     >> MyInteger to be made visible outside the scope of PrivateType ?
>     >> Doesnt it make the code less secure(for example,consider an
>     >> "uninitialized" object of type PrivateType.MyInteger).
> 
>     Jeffrey> Because that's what private means in Ada.
> 
> He does have a point though - some languages will initialise all
> variables to dummy values - this means you can get predictable results
> in code that (wrongly) uses them before setting them to a value.
> 
> In this case it is possible to force initialisation (at least outside
> the package), as per another poster's suggestion, because it is a
> private type. Alternatively it is possible to turn it into a record
> type and provide a default value for the component, as per another
> post.
> 
> In other cases it isn't so easy, e.g. any non-private non-record type.
> 
> In fact, by default (at least last time I checked), gcc (or was that
> gnat) doesn't check the validity of parameters to functions if the
> type matches, even though the type hasn't been initialised and may
> just happen to contain an illegal value.
> 
> I seem to recall Ada will initialise access types to null, and record
> components (if defaults given), but nothing else.

Access variables are initialized to null by language definition. 
Normalize_Scalars pragma exists also, and Gnat has Initialize_Scalars I 
think. These can give more control, but IMHO that's an after-the-bug 
resort.