Groups > comp.lang.java.programmer > #13255

Re: Keeping the split token in a Java regular expression

From	Robert Klemme <shortcutter@googlemail.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: Keeping the split token in a Java regular expression
Date	2012-03-28 07:51 +0200
Message-ID	<9tfn68Faj3U1@mid.individual.net> (permalink)
References	<48d35bc3-a391-4ccf-a222-dac64775a2f2@oq7g2000pbb.googlegroups.com> <2pvclq9lll.fsf@shell.xmission.com> <cc5b2412-cf3f-4f74-8eea-c3484117e8f5@w6g2000pbp.googlegroups.com> <2pr4we9ii3.fsf@shell.xmission.com> <Y6mcr.27182$QC3.4987@newsfe16.iad>

Show all headers | View raw

On 03/27/2012 06:43 PM, Daniel Pitts wrote:
> On 3/27/12 8:21 AM, Jim Janney wrote:
>> laredotornado<laredotornado@zipmail.com> writes:
>>
>>> On Mar 27, 9:15 am, Jim Janney<jjan...@shell.xmission.com> wrote:
>>>> laredotornado<laredotorn...@zipmail.com> writes:
>>>
>>> Jim, That's absolutely brilliant and does exactly what I want in a
>>> short amount of code.
>>>
>>> Stefan, thanks for your solution as well. I tried that out first and
>>> it works too. - Dave
>>
>> It turns out that lookbehind only works with some patterns; the engine
>> has to be able to determine the length of the match in advance. Not
>> surprising when you think about it. It's an interesting question and
>> gave me a reason to learn something new.
>>
> That's interesting. I've written my own Deterministic FSA to implement a
> subset of regex functionality, and arbitrary lookbehind actually would
> be an easy feature to add. Easier than zero-width matches (for example
> word-boundaries).

The limitation for lookbehind seems to be quite common (Ruby's Oniguruma 
has it as well).  With arbitrary lookbehind you need a buffer which can 
grow because you must basically operate on the whole string the whole 
time.  And, most modern regular expression engines are implemented as 
NFAs - or better NFA with a lot of special logic stacked onto it.  The 
runtime overhead of two directions of backtracking might be considered 
too big.

Kind regards

	robert

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

Keeping the split token in a Java regular expression laredotornado <laredotornado@zipmail.com> - 2012-03-26 11:54 -0700
  Re: Keeping the split token in a Java regular expression Lew <lewbloch@gmail.com> - 2012-03-26 12:22 -0700
    Re: Keeping the split token in a Java regular expression Robert Klemme <shortcutter@googlemail.com> - 2012-03-26 22:01 +0200
      Re: Keeping the split token in a Java regular expression Arne Vajhøj <arne@vajhoej.dk> - 2012-03-26 21:46 -0400
        Re: Keeping the split token in a Java regular expression Robert Klemme <shortcutter@googlemail.com> - 2012-03-27 23:01 +0200
          Re: Keeping the split token in a Java regular expression Arne Vajhøj <arne@vajhoej.dk> - 2012-03-27 17:18 -0400
          Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-27 14:21 -0700
            Re: Keeping the split token in a Java regular expression Robert Klemme <shortcutter@googlemail.com> - 2012-03-28 07:38 +0200
              Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-28 10:24 -0700
  Re: Keeping the split token in a Java regular expression markspace <-@.> - 2012-03-26 13:49 -0700
  Re: Keeping the split token in a Java regular expression laredotornado@gmail.com - 2012-03-26 14:21 -0700
    Re: Keeping the split token in a Java regular expression markspace <-@.> - 2012-03-26 15:02 -0700
    Re: Keeping the split token in a Java regular expression Knute Johnson <nospam@knutejohnson.com> - 2012-03-26 15:56 -0700
      Re: Keeping the split token in a Java regular expression markspace <-@.> - 2012-03-26 16:02 -0700
        Re: Keeping the split token in a Java regular expression Knute Johnson <nospam@knutejohnson.com> - 2012-03-26 17:33 -0700
          Re: Keeping the split token in a Java regular expression Martin Gregorie <martin@address-in-sig.invalid> - 2012-03-27 01:17 +0000
            Re: Keeping the split token in a Java regular expression Martin Gregorie <martin@address-in-sig.invalid> - 2012-03-27 21:57 +0000
    Re: Keeping the split token in a Java regular expression Gene Wirchenko <genew@ocis.net> - 2012-03-26 18:26 -0700
      Re: Keeping the split token in a Java regular expression Lew <lewbloch@gmail.com> - 2012-03-26 19:07 -0700
        Re: Keeping the split token in a Java regular expression Knute Johnson <nospam@knutejohnson.com> - 2012-03-26 20:40 -0700
          Re: Keeping the split token in a Java regular expression Gene Wirchenko <genew@ocis.net> - 2012-03-27 09:10 -0700
            Re: Keeping the split token in a Java regular expression Lew <lewbloch@gmail.com> - 2012-03-27 11:09 -0700
              Re: Keeping the split token in a Java regular expression Gene Wirchenko <genew@ocis.net> - 2012-03-27 13:32 -0700
                Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-27 14:29 -0700
                Re: Keeping the split token in a Java regular expression Gene Wirchenko <genew@ocis.net> - 2012-03-27 16:22 -0700
                Re: Keeping the split token in a Java regular expression Gene Wirchenko <genew@ocis.net> - 2012-03-27 18:20 -0700
                Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-27 18:27 -0700
                Re: Keeping the split token in a Java regular expression Gene Wirchenko <genew@ocis.net> - 2012-03-27 21:31 -0700
                Re: Keeping the split token in a Java regular expression Robert Klemme <shortcutter@googlemail.com> - 2012-03-28 07:41 +0200
                Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-28 10:28 -0700
  Re: Keeping the split token in a Java regular expression Lew <lewbloch@gmail.com> - 2012-03-26 16:26 -0700
    Re: Keeping the split token in a Java regular expression Knute Johnson <nospam@knutejohnson.com> - 2012-03-26 17:36 -0700
    Re: Keeping the split token in a Java regular expression Robert Klemme <shortcutter@googlemail.com> - 2012-03-27 23:27 +0200
      Re: Keeping the split token in a Java regular expression Robert Klemme <shortcutter@googlemail.com> - 2012-03-28 07:28 +0200
  Re: Keeping the split token in a Java regular expression "John B. Matthews" <nospam@nospam.invalid> - 2012-03-26 20:49 -0400
  Re: Keeping the split token in a Java regular expression Arne Vajhøj <arne@vajhoej.dk> - 2012-03-26 21:58 -0400
    Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-26 21:14 -0700
      Re: Keeping the split token in a Java regular expression Arne Vajhøj <arne@vajhoej.dk> - 2012-03-27 17:21 -0400
        Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-27 15:20 -0700
          Re: Keeping the split token in a Java regular expression Arne Vajhøj <arne@vajhoej.dk> - 2012-03-27 18:48 -0400
            Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-27 17:07 -0700
          Re: Keeping the split token in a Java regular expression Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-27 21:49 -0300
            Re: Keeping the split token in a Java regular expression Arne Vajhøj <arne@vajhoej.dk> - 2012-03-27 20:56 -0400
              Re: Keeping the split token in a Java regular expression Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2012-03-27 22:01 -0300
                Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-27 18:27 -0700
  Re: Keeping the split token in a Java regular expression Jim Janney <jjanney@shell.xmission.com> - 2012-03-27 08:15 -0600
    Re: Keeping the split token in a Java regular expression laredotornado <laredotornado@zipmail.com> - 2012-03-27 07:58 -0700
      Re: Keeping the split token in a Java regular expression Jim Janney <jjanney@shell.xmission.com> - 2012-03-27 09:21 -0600
        Re: Keeping the split token in a Java regular expression Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-03-27 09:43 -0700
          Re: Keeping the split token in a Java regular expression Robert Klemme <shortcutter@googlemail.com> - 2012-03-28 07:51 +0200

csiph-web