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Date: Wed, 03 Dec 2003 20:23:53 -0500
From: "Robert I. Eachus" <rieachus@comcast.net>
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Newsgroups: comp.lang.ada
Subject: Re: Question about OO programming in Ada
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Date: 2003-12-03T20:23:53-05:00
List-Id: <comp.lang.ada>

Hyman Rosen wrote:

> Not on a pointer field within the object, but on the object itself.

I'm very confused about why Hyman is confused.  Making a copy of an 
access value in Ada, and calling Free for both the original and the copy 
is bad juju.  Calling Free twice, or twenty times and passing the only 
the original access object is never a problem.

Ah, I think I get it.  In C there are many occasions where a function 
will return a heap object, and it is up to the caller to free the 
memory.  The returned value can be a copy of the original pointer, so in 
C it is relatively common to free a copy of the original heap pointer. 
That may be what is confusing Hyman.

In Ada is it very rare, and usually an error if you call Free for an 
object or value that was not assigned a value by new.  Normally in 
Finalize procedures this is a record parameter.

Freeing the entire record that was the parameter of a Finalize procedure 
is possible to write,  but you end up assigning Foo'Access to something 
then freeing it.  (If you try to call Free on a access discriminant, it 
won't work.)  As the previous paragraph says, to any Ada programmer that 
looks like big trouble, and it is.

-- 
                                           Robert I. Eachus

100% Ada, no bugs--the only way to create software.