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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: Re: Limited_Controlled types as 'out' arguments
Date: Thu, 31 Jul 2003 07:43:05 +0000 (UTC)
Organization: IKS GmbH Jena
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* Randy Brukardt wrote:
> "Lutz Donnerhacke" <lutz@iks-jena.de> wrote in message
>> which is clearly wrong in the same way.
> 
> Of course. "in out" and "out" parameters for tagged types (and most other
> types as well) are equivalent. Consider the lack of an "in" to be a comment
> to the caller, not to the author of the subprogram.

I thought a call "xxx(my)" to "procedure xxx (a : out Test)" is very similar
to "my := xxx", if a "function xxx return Test" exists.

This idea is wrong.

> not be initialized (esp. if the type isn't controlled), but the object as a
> whole is initialized. If it wasn't, the tag wouldn't be set, which would
> make even membership operations impossible.

Ack for discriminants, tags, etc.
Nack for private data.

So the consequence is: If you pass a controlled type as an 'out' paramenter
in the type defining library unit, provide sufficient initialization for all
private data, otherwise you can't distiguish uninitalized garbage from real
data.

>> So the only result of this can be: Do not provide 'out' Parameters to
>> controlled types in the same library unit.
>
> No, just realize that "out" is the same as "in out" as far as the
> implementation of a routine is concerned. But it still can provide useful
> information to the caller.

I'm going to see this, but I'm still confused.