[gtkada] configuration files

[Stephen Leake]

Preben Randhol <randhol at pvv.org> writes:

> Jacob Sparre Andersen <sparre at nbi.dk> wrote on 28/05/2002 (13:44) :
> > It looks reasonable execept for a few details:
> > 
> >  * I would like to have the option of reading the settings
> >    from a prioritised list of configuration files, and not
> >    just a single named file.
> 
> Do you want the pacakge to search through the files over and over again
> to find the value you want?

Hmm, interesting point. I would assume that the search would just be
for a file, and the first file found would be used after that.

> >  * It would be practical to include a function for reading
> >    the configuration file(s) into a suitable data structure,
> >    so the files only need to be read once during the
> >    execution of a program.
> 
> Why do we need to do it some complicated? This sounds like XML.

XML is a file format, not an in-memory format. Ah, I guess you mean
the object model used by XML parsers. Yes, it does start to sound like
that. We don't want to go too far in that direction.

I see no need to make the in-memory format visible to clients of the
config file package.

> First settings files change from version to version of the program.
> So the first thing we need to do is to
> 
>    1) Find out that this is a config file for this program
>    2) Which version of the program

This can be handled by making one of the keys be "version". I don't
think we need to standardize this behavior.

Although I guess it could influence the search path. That can be
handled by having the application set the search path before looking
for the file.

>    procedure Read_Settings 
>       (Version : Float) 
>    is
>    -- ...
>    begin
>       if Version <= 1.0 then
>          Read ("Directory.Help", Help_Directory);
>          Read ("Directory.Graphics", Graphics_Directory);
>          Read ("Entry.Max_Value", Max_Value);
>       elsif Version > 1.0 and Version <= 2.0 then
>          Read ("Directory.Help", Help_Directory);
>          Read ("Directory.Graphics", Graphics_Directory);
>          Read ("Directory.Data", Data_Directory);
>          Read ("Entry.Max_Value", Max_Value);
>          --  etc
>       end if;
> 
>    end Read_Settings;

Yes, I have code like this in my Windex applications. But I don't
think it needs to be standardized in the package.

> The program will be writing and reading the settings files so the
> programmer knows the order in which the data comes. There is no need
> to add extra dynamic. If there is a mistake in the settings file a
> Program_Error should be raised I think.

Some other exception would be more appropriate. Perhaps
Config_Files.Configuration_Error?

-- 
-- Stephe