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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: How can one record component be local and another not?
Date: Tue, 5 May 2020 14:48:27 +0300
Organization: Tidorum Ltd
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Date: 2020-05-05T14:48:27+03:00
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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).

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

It did not work for me (same error message) if I just added "aliased", 
making "r : aliased in out Rec", although I think that should also be 
enough to ensure pass by reference.

This was on GNAT Community 2019 (20190517-83), Mac.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .