[Mono-dev] Program Option Parsing Library

Jonathan Pryor jonpryor at vt.edu
Fri Jan 11 06:26:47 EST 2008

On Thu, 2008-01-10 at 14:39 -0800, Jay Logue wrote:
> Jonathan Pryor wrote:
> > I don't see how an out parameter would be better than a return value,
> > especially considering that every other .Parse() method in the framework
> > actually returns a value.
> >   
> This is probably well into the realm of personal preference

Indeed.  I like return values. :-)

Which just leaves the question of what _type_ of return value:
List<string> or string[].  Currently I'm using List<string> because (I
figure) it'll require less memory duplication, as I can use a
List<string> internally to store the unprocessed arguments.  For a
string[] I'd *still* use a List<string> internally, there would just be
a final `list.ToArray();', which creates a new array...

I'm also not going to have a TryParse() overload, as it would provide no
information about why parsing failed.

> you want to make the error handling very straightforward and
> boilerplate (so people are likely to get it right).   To that end, if
> you do end up adding a special exception type, I would have the
> Exception.Message value be exactly what should appear on stderr.
> E.g.:
>         int verbose = 0;
>         Options p = new Options () {
>             { "v", v => ++verbose },
>             { "h|?|help", v => ShowHelp () }
>         };
>         try {
>             p.Parse(args);
>         }
>         catch (OptionException ex) {
>             Console.Error.WriteLine("foo: {0}", ex.Message);
>             Console.Error.WriteLine("Try 'foo --help' for more
> information");
>             return 1;
>         }

Done.  Test.CheckExceptions() now checks the exception message, so you
can see what kind of messages are now produced.

Attached is a new version of Options.cs.  Major changes:

  - Type conversion error messages are more useful.
  - New OptionException type thrown when parsing fails instead of
  - Options.Parse() returns List<string> of unhandled options.
  - Better Option argument checking.

Now how should localization be handled?  Should it?

 - Jon

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