Re: Qs re 'Write & 'Read

["David C. Hoos" <david.c.hoos.sr@ada95.com>]

<tmoran@acm.org> wrote in message news:YDeFa.929408$Zo.212966@sccrnsc03...
> Is the default 'Write on a non null access type supposed to write the .all
> and a 'Read supposed to do an allocate and read in the .all value?
> Same questions for generall access types.
No.  The actual access value is written to the stream -- not very useful.

However, I have been using stream attribute override procedures like these
for years:

   -----------------------------
   -- Translation_Access_Read --
   -----------------------------

   procedure Translation_Access_Read
     (The_Stream_Access : access Ada.Streams.Root_Stream_Type'Class;
      The_Translation_Access : out Translation_Access)
   is
      Is_Non_Null : Boolean;
   begin
      Boolean'Read (The_Stream_Access, Is_Non_Null);
      if Is_Non_Null then
         The_Translation_Access := new Translation'
           (Translation'Input (The_Stream_Access));
      else
         The_Translation_Access := null;
      end if;
   end Translation_Access_Read;

   ------------------------------
   -- Translation_Access_Write --
   ------------------------------

   procedure Translation_Access_Write
     (The_Stream_Access : access Ada.Streams.Root_Stream_Type'Class;
      The_Translation_Access : Translation_Access)
   is
   begin
      if The_Translation_Access /= null then
         Boolean'Write (The_Stream_Access, True);
         Translation'Output
           (The_Stream_Access, The_Translation_Access.all);
      else
         Boolean'Write (The_Stream_Access, False);
      end if;
   end Translation_Access_Write;

The idea is that in a similar fashion to the way that for unconstrained
string types
the string itself is preceded by its contstraint, access types are written
to the
stream with a boolean value preceding the data (if any).

It surely seemed to me like the language standard could have defined
something
like this as the default for access types, but alas, it did not.

I'm not sure why i didn't make these procedures as part of a generic package
to
be instantiated with two parameters -- the data type and its access type,
but
this is what I've been using, lo these several years.


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