From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	ip-172-31-74-118.ec2.internal
X-Spam-Level: 
X-Spam-Status: No, score=-0.5 required=3.0 tests=BAYES_05,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM,NICE_REPLY_A autolearn=ham autolearn_force=no
	version=3.4.6
Path: eternal-september.org!reader02.eternal-september.org!.POSTED!not-for-mail
From: Rod Kay <rodakay5@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Did I find a (nearly-)gotcha here?
Date: Sat, 13 Nov 2021 19:53:57 +1100
Organization: A noiseless patient Spider
Message-ID: <smnuf8$s9h$1@dont-email.me>
References: <29091147-1b81-4a3b-a646-c6a6d1ebe4ean@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Sat, 13 Nov 2021 08:54:00 -0000 (UTC)
Injection-Info: reader02.eternal-september.org; posting-host="a2d1a6d5065b31d0de62bb10b5ac60ab";
	logging-data="28977"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/NUkywCaN5/B1BU8Z889rJ+JPlfoWxSqk="
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.3.0
Cancel-Lock: sha1:Cq8dkyjpCy7GnGw2opkhdOBFrzk=
In-Reply-To: <29091147-1b81-4a3b-a646-c6a6d1ebe4ean@googlegroups.com>
Content-Language: en-US
Xref: reader02.eternal-september.org comp.lang.ada:63117
List-Id: <comp.lang.ada>

On 13/11/21 18:46, reinert wrote:
>
>     procedure test_a(ok :    out Boolean) is
>     begin
>        if false then
>           ok := true;
>        end if;
>     end test_a;
> 
> I get the following output (using GNAT Community Edition):
> 
> ok_a = FALSE
> ok_b = TRUE
> 
> As far as I understand, this is correct.
> However, I think I remember that (some) older versions of the GNAT compiler gave a different result. Could others try?  And does my program example reveal an unnecessary gotcha?
> 
> reinert
> 

Hi reinert,

    The value of an 'out' only parameter needs to be explicitly set. The 
initial value of the 'ok_a' variable will be discarded and then set to 
the value of the 'ok' parameter within 'test_a' when the call completes. 
Since 'ok' is not set in 'test_a' it's value is indeterminate (and 
therefore erroneous).

    I'd expect GNAT to issue a warning. Probably you need to add a flag 
to GNAT to enable that warning. Perhaps try adding '-gnatwa'.


Regards.