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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Warnings about hiding
Newsgroups: comp.lang.ada
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 <op.vkabvkw30k3wt7@jellix.jlfencey.com> <i8p3e5$pdl$1@munin.nbi.dk>
Date: Sat, 9 Oct 2010 10:08:17 +0200
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Date: 2010-10-09T10:08:14+02:00
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On Sat, 9 Oct 2010 01:51:47 -0500, Randy Brukardt wrote:

> "Vinzent Hoefler" <nntp-2010-10@t-domaingrabbing.de> wrote in message 
> news:op.vkabvkw30k3wt7@jellix.jlfencey.com...
> ...
>> JFTR: If you move "Finalize" into the public part, the warning for it
>> disappears (just tested with GNAT GPL 2010).
>>
>> (IMO, there's no point putting it in the private part, the operation
>> is already known, anyway.)
> 
> My opinion is exactly the reverse: there is no point in putting it in the 
> visible part in this case -- it should not matter to clients whether or not 
> the subprogram is overridden, so why burden them with it??

It does matter:

1. Clients dealing with specific types shall be able to call manifested
operations of the type.

2. Clients which publicly derive from a parent type must call the parent's
Finalize from their implementations of Finalize.

> That assumes of course that the clients are smart enough (or have good 
> tools) which can show them what is actually inherited. In the absense of 
> that, you really have to override everything in the public part, whether you 
> want to or not, else no one will know that the operations even exist - no 
> one can figure out by hand what's inherited. (I vote for good tools. :-)

I vote for language fixes:

1. Finalize in the role of a destructor shall not be callable at all

2. When overridden the parent's implementation of Finalize shall be called
automatically.

3. Private overriding of a public interface shall be illegal. I.e. if Foo
is a public operation of T then either so:

   type S is new T with private;
   overriding procedure Foo (X : T);

or else so:

   type S is private;
private
   type S is new T with ...;
   overriding procedure Foo (X : T);

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de