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From: "Nick Roberts" <nickroberts@blueyonder.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: generic imports?  void* -> generics?
Date: Fri, 19 Sep 2003 22:18:04 +0100
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Date: 2003-09-19T22:18:04+01:00
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"chris" <spamoff.danx@ntlworld.com> wrote in message
news:FBIab.3309$DM5.35123@newsfep4-glfd.server.ntli.net...

> Should the following C code be mapped to a generic?
>
> void *lua_touserdata (Lua_State* L, int pos)

Not directly. I would suggest that you take the following approach.

   package Stream_C_Pointers is new Interfaces.C.Pointers(
      Index => Ada.Streams.Stream_Element_Offset,
      Element => Ada.Streams.Stream_Element,
      Element_Array => Ada.Streams.Stream_Element_Array );

   subtype Stream_C_Pointer is Stream_C_Pointers.Pointer;
   use Stream_C_Pointers;

   function LUA_To_User_Data (State: access LUA_State;
                                  Pos: Interfaces.C.int) returns
Stream_C_Pointer;

   pragma Import(C,LUA_To_User_Data,"lua_touserdata");

The general idea is that Ada code is able to read a variable from the memory
area returned by this C function, interpreted as a stream array so that the
variable's stream-oriented Read procedure or Input function can be used
directly. There could well be difficulties associated with writing data
using C code and then reading it using (stream-oriented) Ada code.

You may well wish to wrap all this up in a package or a generic package, at
a higher level of organisation.

Hope this helps. I'd be happy to give more detail if you wish.

--
Nick Roberts
Jabber: debater@charente.de [ICQ: 159718630]