From: Randy Kramer <rhkramer@...>
Date: 2005-04-03T23:10:48+09:00
Subject: Re: Iterating through a string and removing leading characters

On Sunday 03 April 2005 09:36 am, Saynatkari wrote:
> Le 3/4/2005, "Mathieu Bouchard" <matju@sympatico.ca> a �crit:
> >However if I were to solve the problem of finding which sub-regexp has
> >been matched in (A|B|C|...), I'd edit re.c and add a (?)-feature for
> >filling a $-slot with a value that doesn't come from the string, e.g.
> >
> >/((?"Aah"(A))|(?"Bay"(B))|(?"Say"(C))|(?"Day"(D)))/
> >
> >Would put one of "Aah", "Bay", "Say", "Day" strings in $2...
> >
> >But this doesn't make sense yet, as one would expect it to instead be put
> >in one of $2, $4, $6, $8, ... to be consistent with current regexp
> >semantics; and looking up possibly all of those looking for a nonnil
> >$-slot is a O(n)-time thing. There ought to be a better way, that is,
> >something both fast and consistent with current semantics, but I can't
> >think of any as of now. Do you have any ideas? If you have something good
> >then I think it should be a RCR.

I like this idea (I think it would be helpful with my problem of fast parsing 
of TWiki markup).  (And, if I decide to do a character by character thing 
myself in c, it sounds like re.c would be something to study.)

But, instead of (or maybe in addition to) returning the "Aah", "Bay" in $2, $4 
or whatever, how about returning an integer (somehow) that indicates which 
one matched?  

As a Ruby newbie, I'm not sure that's all I'd be looking for--if Ruby gives me 
a way to access those strings directly by the integer, that would be great.  
For example, say the integer is returned as $a (to avoid collision with $1, 
$2 ...).  I'd like to be able to access the "Aah", "Bay, ... by something 
like $($a)--barring that, I can simply maintain a separate array of the 
"Aah"... and access that array using $a.

Randy Kramer

>
> This is a worthy idea, certainly! I should not expect it to cause
> any confusion so long as the notation is standardised, particularly
> through the standard ? extension switch. Perhaps the inner braces
> would not be allowed for clarity? Unfortunately the rubyish ?!
> (in-place method) and ?# (string interpolation) are already taken :)
>
> /(?-> 'match' 'replacement')/