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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Limited use for limited with?
Date: Wed, 29 Sep 2010 08:03:38 +0200
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Message-ID: <8762xpgk79.fsf@ludovic-brenta.org>
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Date: 2010-09-29T08:03:38+02:00
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Maciej Sobczak writes on comp.lang.ada:
> Consider:
>
>    procedure Register (X : in Object'Class);
>
> X will be passed by reference, but there is still nothing in the
> signature (apart from the name of the operation) that would suggest
> that the reference will be leaked out of the operation's scope. So the
> user does this:
>
> declare
>    X : My_Concrete_Object;
> begin
>    Register (X);
> endl;
>
> and bang, everything breaks into pieces.

No, because this is Ada :)

Suppose Register does something like (where Registry is a suitably
defined indefinite vector):

procedure Register (X : in Object'Class) is
begin
   Registry.Append (X);
end Register;

This does copy a "hidden" reference to X into the Registry, it copies X
itself (i.e. deep copy).  So there is no leak and the construct is safe.
Not so with explicit access values.

-- 
Ludovic Brenta.