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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Pass by reference
Date: Mon, 12 Apr 2004 12:29:27 +0200
Organization: At home
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Date: 2004-04-12T12:29:27+02:00
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Florian Weimer wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> Because that could be a handle requiring Initialize/Adjust/Finalize. To
>> be honest, forcing tagged types to be by-reference was probably a
>> mistake.
> 
> It's hard to envision another efficient way of implementing
> dispatching calls.

Why? Dispatching does not depend on the way an object is passed. For
example, let you have a by-copy T and Foo (Object : in out T); is a
primitive operaton:

X : T'Class;

Foo (X);
-- Selects Foo according the type tag in X
-- Copies the T part of X (calls Adjust)
-- Calls the selected Foo with the copy
-- Finalizes the T part of X (calls Finalize)
-- Copies possibly modified T back into X (calls Adjust)
-- Finalizes the copy (calls Finalize)

When T is in a register it might be more efficient than by-reference. But
let the compiler decide it knows better.

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de