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,WEIRD_PORT
	autolearn=ham autolearn_force=no version=3.4.4
X-Google-Thread: 103376,ab3fadb7cac7363c
X-Google-NewGroupId: yes
X-Google-Attributes: gida07f3367d7,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news3.google.com!feeder.news-service.com!goblin2!goblin.stu.neva.ru!fi.sn.net!newsfeed1.tdcnet.fi!news.song.fi!not-for-mail
From: Anders Wirzenius <anders.wirzenius@netikka.fi>
Newsgroups: comp.lang.ada
Subject: Re: using `use' : what is the best practice ?
References: <57e75a35-058c-4172-9a3d-e11e7c5f7697@l2g2000prg.googlegroups.com>
Date: Tue, 07 Jun 2011 22:32:54 +0300
Message-ID: <87hb818mjd.fsf@cawu.ok8>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)
Cancel-Lock: sha1:MyQeqBEhm6V07j7OPXBdBOt1XF4=
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Organization: Netikka 
NNTP-Posting-Host: 81.209.10.42
X-Trace: 1307477281 news.netikka.fi 2836 81.209.10.42:46875
X-Complaints-To: abuse@netikka.fi
Xref: g2news1.google.com comp.lang.ada:19688
Date: 2011-06-07T22:32:54+03:00
List-Id: <comp.lang.ada>

milouz <a.michelizza@gmail.com> writes:

> Hi guys,
> Sorry with my annoying questions, but it's not easy to program in Ada
> after 20 years programming in asm / C ;-)
>
> Maybe a not so anecdotic question : when using the 'use' clause ?
>
> My first thought is that using 'use' is not good because it masks the
> package tree.
> For example, if I have 2 packages with procedures sharing the same
> name, example `P1.Foo' and `P2.Foo', my code won't be very readable if
> I only write the short name (`Foo') :
>
>    with P1; use P1;
>    with P2; use P2;
>
>    procedure Main is
>       My_Val : Integer;
>    begin
>       Foo(My_Val);  -- P1 or P2 ?
>    ...
>
> But always avoiding 'use' give some rather obfuscated code, especially
> when using some specific arithmetic operator. For example, playing
> with Address arithmetic without 'use' :
>
>    with System;
>    with System.Storage_Elements;
>
>    procedure Main is
>       A : System.Address;
>       N : Integer;
>    begin
>       A := System.Storage_Elements.To_Address(16#10000#);
>       N := 4;
>  
> System.Storage_Elements."+"(System.Storage_Elements.Storage_Offset(N),
> A);
>    end Main;
>
> The same code with 'use' is more readable :
>
>    with System; use System;
>    with System.Storage_Elements; use System.Storage_Elements;
>
>    procedure Main is
>       A : Address;
>       N : Integer;
>    begin
>       A := To_Address(16#10000#);
>       N := 4;
>       A := A + Storage_Offset(N);
>    end Main;
>
> As I'm very new, I'd like to have your opinion about the way to use
> 'use'.
>
>
>

You may restrict the context of a 'use':

with Text_IO;
procedure Bl is
   A : String := "aaa";
begin
   Text_IO.Put_Line (A);
   declare
      use Text_IO;
      A : character := 'b';
   begin
      Put (A);
   end;
   Put_Line (A);
end;

Try to compile the code. The error message (Gnat) will be:

gnatmake bl.adb 
gcc-4.4 -c bl.adb
bl.adb:12:04: "Put_Line" is not visible
bl.adb:12:04: non-visible declaration at a-textio.ads:263
bl.adb:12:04: non-visible declaration at a-textio.ads:259
gnatmake: "bl.adb" compilation error

-- 
Anders