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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Load an object from a file
Date: Thu, 9 Apr 2009 14:22:24 -0700 (PDT)
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Date: 2009-04-09T14:22:24-07:00
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On Apr 9, 10:32=A0pm, Olivier Scalbert <olivier.scalb...@algosyn.com>
wrote:
> Hi,
>
> I still have one question ...
> How can I implement the Load_Class procedure that will use the Input
> function?
> I do not know how to get the needed stream from a given file name.
> And I do not know how to define the Class_File_Structure result (I get
> an unconstrained subtype (need initialization)).
[...]
> package body jvm is
[...]
> =A0 =A0 =A0procedure Load_Class(File_Name: String) is
>
> =A0 =A0 =A0 =A0 =A0Class_File_Structure: Class_File_Structure_T; -- (unco=
nstrained
> subtype (need initialization)
> =A0 =A0 =A0begin
> =A0 =A0 =A0 =A0 =A0Put_Line(File_Name);
>
> =A0 =A0 =A0 =A0 =A0Class_file_Structure :=3D Input(Stream ???);
>
> =A0 =A0 =A0end Load_Class;
[...]
> end jvm;

Because Class_File_Structure_T is unconstrained and needs
initialization, you cannot use a procedure to load one: out parameters
don't work, and the procedure cannot write into a variable because you
can't declare a variable without initializing it.  So, here is a
possible solution replacing your procedure with a function:

with Ada.Streams.Stream_IO;
...
function From_File (File_Name : String) return Class_File_Structure_T
is
   File : Ada.Streams.Stream_IO.File_Type;
begin
   Ada.Streams.Stream_IO.Open (File,
                               File_Mode =3D>
Ada.Streams.Stream_IO.In_File,
                               Name      =3D> File_Name);
   declare
      Result : constant Class_File_Structure_T :=3D
        Class_File_Structure_T'Input (Ada.Streams.Stream_IO.Stream
(File));
   begin
      Ada.Streams.Stream_IO.Close (File);
      return Result;
   end;
end From_File;

HTH

--
Ludovic Brenta.