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From: hreba <f_hreba@yahoo.com.br>
Newsgroups: comp.lang.ada
Subject: Re: How can one record component be local and another not?
Date: Wed, 6 May 2020 15:13:05 +0200
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Xref: reader01.eternal-september.org comp.lang.ada:58613
Date: 2020-05-06T15:13:05+02:00
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On 5/5/20 10:11 PM, Niklas Holsti wrote:
> On 2020-05-05 22:04, Niklas Holsti wrote:
>> On 2020-05-05 20:32, hreba wrote:
>>> Ok, with all your hints I came to the following solution:
>>>
>>> -- 
>>> package Aux is
>>>     type Integer_P is access all Integer;
>>>     type Rec is limited record
>>>        a: aliased Integer;
>>>        p: Integer_P;
>>>     end record;
>>>
>>>     procedure Init (r: access Rec);
>>> end Aux;
>>> -- 
>>> package body Aux is
>>>     procedure Init (r: access Rec) is
>>>     begin
>>>        r.p:= r.a'Access;
>>>     end Init;
>>> end Aux;
>>> -- 
>>> with Aux;
>>> procedure Test is
>>>     r:    aliased Aux.Rec;
>>> begin
>>>     Aux.Init (r'Access);
>>> end Test;
>>> -- 
>>>
>>> It compiles nicely, and then:
>>>
>>> frank@pc-frank:~/Temp/Test0$ ./test
>>> raised PROGRAM_ERROR : aux.adb:4 accessibility check failed
>>>
>>> #@!!0ßx*~@!!!
>>
>> Ok, apologies if I led you down the wrong path. I admit I did not 
>> build a running program to check my suggestion of the "access" 
>> parameter, and I have not myself often used this kind of code.
>>
>> You should be able to get rid of this error by using 
>> r.a'Unchecked_Access instead of r.a'Access, and then (I think) you can 
>> return to using an "in out" parameter mode instead of "access" mode.
> 
> ... but better make it "aliased in out" to ensure pass-by-reference.

Perfect Niklas, all your proposed variants work!

> I do agree with Dmitry that records with internal pointers-to-component 
> should be "limited" or "controlled".

Did that already, as you can see above.

It was a recurring issue for me but only now I understood it and know 
how to solve it.

Thanks a lot for your help.
-- 
Frank Hrebabetzky, Kronach	+49 / 9261 / 950 0565