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!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: Victor Porton <porton@narod.ru>
Newsgroups: comp.lang.ada
Subject: Re: 'Size hack for enumerated types
Date: Mon, 07 Jul 2014 02:01:40 +0300
Organization: Aioe.org NNTP Server
Message-ID: <lpckgk$6a8$1@speranza.aioe.org>
References: <lp9nc6$no3$1@speranza.aioe.org> <lyk37rcwah.fsf@pushface.org>
 <lp9t79$5pj$1@speranza.aioe.org> <lp9tj0$6ii$1@speranza.aioe.org>
 <ly38eefbkf.fsf@pushface.org>
NNTP-Posting-Host: BISA/P8IHJbAM3ms471zeQ.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7Bit
X-Complaints-To: abuse@aioe.org
User-Agent: KNode/4.12.4
X-Notice: Filtered by postfilter v. 0.8.2
Xref: news.eternal-september.org comp.lang.ada:20755
Date: 2014-07-07T02:01:40+03:00
List-Id: <comp.lang.ada>

Simon Wright wrote:

> Victor Porton <porton@narod.ru> writes:
> 
>> -- rdf-auxilary.ads
>> with Interfaces.C;
>>
>> package RDF.Auxilary is
>>
>>    generic
>>       type Enum_Type is range <>;
>>    package Convert_Enum is
>>       function To_C(Argument: Enum_Type) return Interfaces.C.int;
>>       function From_C(Argument: Interfaces.C.int) return Enum_Type;
>>    end;
>>
>> end RDF.Auxilary;
> 
> If you want Enum_Type to be an enumeration, you should use a formal
> discrete type definition[1]:
> 
>    type Enum_Type is (<>);

The same error with this.

BTW, remind me what is the difference of:
- type Enum_Type is range <>;
- type Enum_Type is (<>);
?

> But I don't see what you're trying to achieve that can't easily be done
> using simple language facilities:
> 
>    with Ada.Text_IO; use Ada.Text_IO;
>    procedure Enums is
>       type Flag_Type is (Libxml_Error_Save,
>                          Libxml_Structured_Error_Save,
>                          URI_Interning,
>                          WWW_Skip_Init_Finish) with Convention => C;
>       for Flag_Type use (Libxml_Error_Save => 1,
>                          Libxml_Structured_Error_Save => 2,
>                          URI_Interning => 3,
>                          WWW_Skip_Init_Finish => 4);
>       function Increment (F : Flag_Type) return Flag_Type
>       with Import, Convention => C, External_Name => "increment";
>    begin
>       Put_Line ("incremented "
>                   & Libxml_Structured_Error_Save'Img
>                   & " is "
>                   & Increment (Libxml_Structured_Error_Save)'Img);
>    end Enums;

I see no reason for Increment function to work well with Convention => C, it 
seems that you are lucky with your compiler.

After all Flag_Type and enum flag_type may be of different size!

> and, in increment.c,
> 
>    #include <stdio.h>
> 
>    typedef enum {LIBXML_ERROR_SAVE = 1,
>                  LIBXML_STRUCTURED_ERROR_SAVE,
>                  URI_INTERNING,
>                  WWW_SKIP_INIT_FINISH} flag_type;
> 
>    flag_type increment(flag_type f) {
>      flag_type result = f;
>      ++result;
>      printf("increment received %d, returning %d\n", f, result);
>      return result;
>    }
> 
> with
> 
>    $ gcc -c increment.c
>    $ gnatmake enums.adb -largs increment.o
>    $ ./enums
>    increment received 2, returning 3
>    incremented LIBXML_STRUCTURED_ERROR_SAVE is URI_INTERNING
> 
> [1] http://www.ada-auth.org/standards/12rm/html/RM-12-5-2.html#p2

-- 
Victor Porton - http://portonvictor.org