From: Kyle Schmitt <kyleaschmitt@...>
Date: 2008-05-14T06:32:35+09:00
Subject: Re: detail on a regex?

Hum.  Yea, but I want the error messages to be helpful for when I'm
not the one running the program.
And also somewhat unique to the reason the error was thrown, just in
case I need to track it down and find out there's a logic error on my
part.

Not that that ever happens.......

On Tue, May 13, 2008 at 11:45 AM, Robert Klemme
<shortcutter@googlemail.com> wrote:
>
> On 13.05.2008 17:59, Kyle Schmitt wrote:
>
> > Is there a way to pull details out of a regular expression's failure?
> >
> > I'm running into a situation where I've got some validation methods,
> > and I'm resorting to passing in both a regular expression and a range.
> >  I know quite well I could just use a range inside of a regex, and
> > would rather, but I need to get the range in order to have some useful
> > error messages.
> >
> > For example, the string must be 3 to 8 characters long, start with a
> > letter, and may contain letters numbers or dashes.
> >
> > I would like to just use this:
> > some_string=~/^[a-z][-a-z0-9]{2,7}$/i
> >
> > But if the match fails, I can't give out any good error messages
> > without further inspecting the string, so I end up with
> > some_string=~/^[a-z][-a-z0-9]$/i
> > [3..8].include?some_string.length
> >
> > Just so I can give reasonable error messages.
> >
>
>  If it does not match you get no information out of the regexp.  The
> simplest would be to just include the string in an error message.  To avoid
> ugly errors with lengthy strings you could add a length check before the
> regexp match.
>
>  In some cases it might be possible to build the regexp so that it matches
> chunks:
>
>
>  some_string=~/^([a-z])?([-a-z0-9]{2,7})?(.*)$/i
>
>  Now you have a match if $1 and $2 are non nil and $3 is empty.
>
>  HTH
>
>         robert
>
>