From: Garance A Drosehn <drosihn@...>
Date: 2005-08-02T05:52:58+09:00
Subject: Re: Defining regexp's and variables set by them

On 8/1/05, Garance A Drosehn <drosihn@gmail.com> wrote:
>
> The downside to this is that the regular-expression is now
> defined somewhere "far away" from the when-clause that
> uses it.  After some testing I may need to make changes to
> the regexp, such as:
> 
>     re_simple = Regexp.new('(check|test) (\d+)')
> 
> The thing is, by changing 'check' to '(check|test)', I have to
> remember that the when clause also needs to change from
> referencing $1 to referencing $2.  [...]
> 
> I was kinda wondering if it would make sense for ruby to
> support something like:
> 
>     re_simple = Regexp.new('check (\d+)') { cnum = $1 }
> 
> so I could then have the when clause say:
> 
>             when re_simple
>                 check_number = cnum
> 
> I realize this is a trivial example, but as the expressions get
> more involved, and the case-statement has many when's, it
> would be nice if I could have the compiled regular-expression
> set values on variable names that *I* pick, in addition to the
> standard values in a MatchData object.

I thought about this some more after going home and getting
some sleep...  One obvious question is what would be the
scope of the commands inside the { ...code-fragment...}.  It
also occurred to me that I sometimes I make a match, and
then I pass around the resulting MatchData object to other
methods, and *they* do things based on info in MatchData.

So, I came up with this idea:

Allow MatchData to include some user-settable value,
which would initially be set to 'nil' at the time of the match.
And then support:

    re_simple = Regexp.new('check (\d+)') { |mdata|
        mdata.userdata = mdata[1]
    }

or:

    re_simple = Regexp.new('check (\d+)') { |mdata|
        mdata.userdata = Hash.new
        mdata.userdata["cnum"] = mdata[1]
        mdata.userdata["otherval"] = mdata[7]
    }

That way, all the variables that the user is setting will
be tied to the appropriate MatchData object.

I almost think I could implement this by creating my own
subclasses for Regexp and MatchData...

-- 
Garance Alistair Drosehn     =             drosihn@gmail.com
Senior Systems Programmer               or   gad@FreeBSD.org
Rensselaer Polytechnic Institute;             Troy, NY;  USA