From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!news.uzoreto.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: hreba <f_hreba@yahoo.com.br>
Newsgroups: comp.lang.ada
Subject: Re: How can one record component be local and another not?
Date: Tue, 5 May 2020 15:44:33 +0200
Message-ID: <hhd8u1Fg3r4U1@mid.individual.net>
References: <hhcvilFe4qrU1@mid.individual.net>
 <hhd24bFemc4U1@mid.individual.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
X-Trace: individual.net FMOeCaoKTWmR7TRWdsyX3AOBskoK/KuHJN076siUGbiRtFGboU
Cancel-Lock: sha1:GAVYIvekYqwF4r0K2pYBb2+sXfI=
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
In-Reply-To: <hhd24bFemc4U1@mid.individual.net>
Content-Language: de-DE
Xref: reader01.eternal-september.org comp.lang.ada:58588
Date: 2020-05-05T15:44:33+02:00
List-Id: <comp.lang.ada>

On 5/5/20 1:48 PM, Niklas Holsti wrote:
> On 2020-05-05 14:04, hreba wrote:
>> I have reduced my problem to the following example:
>>
>> package Aux is
>>     type Integer_P is access all Integer;
>>     type Rec is record
>>        a: aliased Integer;
>>        p: Integer_P;
>>     end record;
>>
>>     procedure Init (r: in out Rec);
>> end Aux;
>>
>> package body Aux is
>>     procedure Init (r: in out Rec) is
>>     begin
>>        r.p:= r.a'Access;  -- <-- error!
>>     end Init;
>> end Aux;
>>
>> Compiling results in "non-local pointer cannot point to local object" 
>> indicating the marked line above.
>>
>> How can one record component be local and another not?
>>
>> Intention is to have a library subprogram Init() for initialization. 
>> How would I implement that instead?
>>
>> (The reason for the above construction is the need to pass a pointer 
>> to a C library function.)
>>
> 
> The parameter "r" might be passed by copy, in which case the r.a'Access 
> would point to the local copy, and become a dangling pointer on return 
> (copy-out).

Now I understand.

> It works if you replace "r: in out" with "r : access", which ensures 
> pass by reference.

Perfect, works indeed. Thanks a lot.

I tried another thing too: Changed Init into a constructor function 
returning r in an extended return statement. Didn't work. So even an 
extended return statement seems to create a local copy first.

-- 
Frank Hrebabetzky, Kronach	+49 / 9261 / 950 0565