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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada & Postgresql
Date: Mon, 6 Sep 2004 15:19:07 +0200
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Date: 2004-09-06T15:19:07+02:00
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On Mon, 06 Sep 2004 13:43:56 +0100, Marius Amado Alves wrote:

>> ...I can't pinpoint now what annoying Ada 95 feature 
>> I was escaping back in 2001 when I wrote this package and its 
>> applications. Never mind. Just write Pgsql_Controlled.
> 
> OK, I just took the time to write this. While I'm at it, I'll control 
> also Db_Type, to call Close on finalization. Oops, no, Ada 95 does not 
> let me do that, it makes
> 
>     function Execute (Db: Db_Type; Command: String) return Result_Type;
> 
> illegal, because an "operation can be dispatching in only one type."

Well, Ada does not have multiple dispatch...

> This is one of many examples of what I call "Ada getting in the way."

But very probably it is not what you actually need. I suppose that the
Result_Type'Class hierarchy (if any) is independent to one of
Db_Type'Class. So the Execute could be contravariant in its result:

function Execute (Db: Db_Type; Command: String)
   return Result_Type'Class;

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