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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Modes (was unbounded_string)
Date: Mon, 13 Oct 2003 12:12:43 +0200
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Date: 2003-10-13T12:12:43+02:00
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On Mon, 13 Oct 2003 09:40:39 GMT, "Stephane Richard"
<stephane.richard@verizon.net> wrote:

>"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>news:94skovca8efqisiip65q37of63g28n1284@4ax.com...
>> On Fri, 10 Oct 2003 19:06:00 GMT, Jeffrey Carter <spam@spam.com>
>> wrote:
>>
>> >Since GNAT.OS_Lib.Getenv returns type String_Access, you have to use
>> >String_Access if you want to use Getenv. But note the description of
>> >Getenv from GNAT.OS_Lib:
>> >
>> >--  Get the value of the environment variable. Returns an access
>> >--  to the empty string if the environment variable does not exist
>> >--  or has an explicit null value (in some operating systems these
>> >--  are distinct cases, in others they are not; this interface
>> >--  abstracts away that difference. The argument is allocated on
>> >--  the heap (even in the null case), and needs to be freed explicitly
>> >--  when no longer needed to avoid memory leaks.
>>
>> Awful, I didn't expected that from ACT. The design above is definitely
>> not Ada's idiom.
>>
>> ---
>> Regards,
>> Dmitry Kazakov
>> www.dmitry-kazakov.de
>
>Perhaps as in many OS it's the only way as the OS (probably written in C or
>some other language simply returns it this way?

In which way? Neither Win32 nor UNIX getenv require to call free on
the result. It just returns a pointer to some chunk of memory which
probably cannot be deallocated at all. Then even if a particular OS
requires further deallocation then it is not Ada's deallocation. It is
freeing resources, which has nothing to do with calling a deallocator
on the result. If a resource has to be freed then we either

1. return a copy and free the resource before return;

2. return a controlled object, which will free the resource upon
destruction.

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de