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Date: Sat, 30 Jun 2007 14:33:24 +0200
From: Georg Bauhaus <bauhaus.rm.tsoh@maps.futureapps.de>
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Subject: Re: Bus error
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Date: 2007-06-30T14:30:01+02:00
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Adam Beneschan wrote:
> On Jun 29, 2:42 am, Georg Bauhaus <bauh...@futureapps.de> wrote:
>> Maciej Sobczak wrote:
>>
>>> Yes, or even stricter:
>>>     with Ada.Finalization; use Ada;
>>>     package P is
>>>         type T (<>) is limited private;
>>>     private
>>>         type T is new Finalization.Limited_Controlled with ...;
>>>     end P;
>>> which prevents uninitialized objects.
>> Uhm, it prevents uninitialized objects that cannot otherwise
>> have default initialisation (e.g. from function calls whose
>> results are assigned to components), or initialisation via Initialize.
>> Such as records that need their components initialised with
>> values known only at run time *and* defined at library level etc.
> 
> I'm not sure what you mean here... For packages that can only see the
> partial view of T, T is an indefinite type, and you cannot declare a
> variable of type T without an initialization expression (3.3.1(5)).  I
> think that's what Maciej was referring to.  (Yes, a private child
> package of P could declare a variable of type T without an
> initializer, but I don't think he was referring to those.)

I was only thinking of guaranteed initialisation of an object of a
limited type T that is declared just anywhere even when it is not
explicitly initialised. The idea being that T then doesn't necessarily
need (<>) in its public view because T's default initialization
might take care of all components via

  type T is limited ...
     Xyz_Part : D := Init_All_Copmonents(T'access, ...);

This, I thought, is made possible through the venerable
mechanisms "limited" and visibility control. That is, just like we can
make a no-argument constructor of a Java class call methods on "this",
we can make variables of a limited type T call functions on "T'access"
(by not using an Ada 2005 constructor function in this case).

And I'm glad that we can now have aggregates of limited types for
building connected (partially) immutable data structures in source.
And all kinds of constants of limited types.