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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: 'Size hack for enumerated types
Date: Sun, 06 Jul 2014 08:22:29 +0100
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Date: 2014-07-06T08:22:29+01:00
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Victor Porton <porton@narod.ru> writes:

> Simon Wright wrote:
>>> What is a better way to do this?
>> 
>> Just use convention C:
>> 
>>    type Flag_Type is (Libxml_Error_Save,
>>                       Libxml_Structured_Error_Save,
>>                       URI_Interning,
>>                       WWW_Skip_Init_Finish) with Convention => C;
>
> Your code does not allow to assign particular numbers to the
> enumeration literals. :-(

I just didn't put that in since you already had it.

   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);
      F : Flag_Type;
      I : Integer with Address => F'Address, Import => Ada;
   begin
      Put_Line ("'Size:       " & Flag_Type'Size'Img);
      Put_Line ("'Object_Size:" & Flag_Type'Object_Size'Img);
      Put_Line ("F'Size:      " & F'Size'Img);
      F := URI_Interning;
      Put_Line ("F:            " & F'Img);
      Put_Line ("I:           " & I'Img);
   end Enums;

(sorry about the hidden unchecked conversion) resulting in

   $ ./enums 
   'Size:        3
   'Object_Size: 32
   F'Size:       32
   F:            URI_INTERNING
   I:            3