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From: "Martin Dowie" <martin.m.dowie@no.spam.ntlworld.com>
Newsgroups: comp.lang.ada
References: <1s7V6.4021$Il5.510814@newsread1.prod.itd.earthlink.net>
Subject: Re: Circular type definition problem
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Date: Mon, 11 Jun 2001 21:16:27 +0100
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Date: 2001-06-11T21:16:27+01:00
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you could split out the implementation specifics into a seperate package
e.g.

with System.Direct_IO;

package Project_Specifics is

   -- Specific to GNAT
   --
   Direct_IO_Count_Last : constant := System.Direct_IO.Count'Last;

end Project_Specifics;


with Ada.Direct_Io;
with Project_Specifics;

package Temp is

   type Byte is mod 256;

   type Block;

   type Blockdata is array (0 .. 511) of Byte;

   type Node_Count is range 0 .. Project_Specifics.Direct_IO_Count_Last;

   type Block is
      record
         Next_Node : Node_Count;
         Data      : Blockdata;
      end record; -- Block

   pragma Pack(Blockdata);
   pragma Pack(Block);

   package Node_Io is new Ada.Direct_Io(Block);
   use Node_Io;

end Temp;


"Charles Hixson" <charleshixsn@earthlink.net> wrote in message
news:1s7V6.4021$Il5.510814@newsread1.prod.itd.earthlink.net...
> This is what I'm trying to do:
>         type Block;
>         package Node_IO is      new Ada.Direct_IO(Block);
>         use     Node_IO;
>         type    BlockData       is      array (0..511) of Byte;
>         type    Block   is      record
>                 next_node       :       Node_IO.Count;
>                 data                    :       BlockData;
>         end record;     --      Block
>         pragma pack(BlockData);
>         pragma pack(Block);
>
> Not too much to my surprise, it didn't work.  Node_IO needs to be
> defined with a real type.  OTOH, the type Node_IO.Count is
> defined within Node_IO, so I can't put it after the declaration
> of Block.
>
> I suppose that I could just give up, and declare next_node to be
> Long_Integer, but that seems so inelegant.  Node_IO.Count is,
> essentially, an Access variable (it says where in the file to
> find the next Block).  But I'm not really sure how to approach
> this.  Any suggestions?