Re: A standard package for config files is needed

[Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>]

dennison@telepath.com (Ted Dennison) writes:

> Preben Randhol <randhol+abuse@pvv.org> wrote in message
> news:<slrnaffafb.27t.randhol+abuse@kiuk0156.chembio.ntnu.no>...

> > One thing I'm sitting and thinking about now is if it is possible to
> > make a procedure for storing a record or array and reading this back. I
> > mean a generic procedure.
> 
> It'd be pretty easy, as long as the generic can own the array type.

Yes. My current Ada binding to the Windows ini API has:

   generic
      type Private_Type is limited private;
      Max_Width : Natural; -- maximum width of Image of Item.
      with function Value (Image : in String) return Private_Type;
   function Read_Private
      (File    : in String;
       Section : in String;
       Keyword : in String;
       Default : in Private_Type)
       return Private_Type;
   -- Return private value associated with Keyword from Section in File. If
   -- Keyword is not found, Default is returned.

   generic
      type Private_Type is limited private;
      with function Image (Value : in Private_Type) return String;
   procedure Write_Private
      (File    : in String;
       Section : in String;
       Keyword : in String;
       Item    : in Private_Type);
   -- Write private value Item to Keyord in Section in File.

The problem with this is that the file syntax for structured values is
now controlled by the client, and is thus not standard. Maybe that's
not really a Bad Thing.

> Hmmm. One thing I'm thinking is that this task might be a bit easier
> if the new version of Ada had the following:
> 
>   o  The ability to specify the 'Image routine for user-defined types.
>   o  'Image being defined by default to perform a 'Image on each
> component of a composite type (in order).

We had a thread on this not long ago. The upshot was "just define an
Image function". Getting the compiler to compose it for you is just
not worth it, and also not going to happen.

I may look into creating a variant of Auto_Text_IO that generates
code to write aggregates to strings, rather than files; that would
simplify this issue somewhat.

-- 
-- Stephe