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From: Maciej Sobczak <see.my.homepage@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Limited use for limited with?
Date: Tue, 28 Sep 2010 14:57:49 -0700 (PDT)
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Date: 2010-09-28T14:57:49-07:00
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On 28 Wrz, 15:45, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:

> > Hiding the use of access values behind the scenes (by virtue of tagged
> > types being always passed by reference) would obstruct the code
> > without clear benefit.
>
> The benefit is clear - no access types.

There are still access types. The fact that they are not explicitly
seen in operation signatures just makes it more obscure. No benefit.

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.

Whereas this:

   procedure Register (X : Object_Access);

at least forces the user to think about scopes. I therefore consider
it to be a safer construct.

> You should register the object itself rather than its pointer. Use a
> constructing function which registers the object by placing it in a list or
> do an explicit call to Register.

No way. There are many Registers and it's up to the user to decide
where the given object should be registered; constructor has no such
knowledge.
And *when* it should be registered, which is not necessarily at
construction time.

> I tend to avoid "all" everywhere I can.

Apparently here I cannot.

--
Maciej Sobczak * http://www.inspirel.com