From: Robert Klemme <shortcutter@...>
Date: 2007-11-19T06:45:03+09:00
Subject: Re: Count substrings from a string

On 18.11.2007 19:57, Robert Dober wrote:
> On Nov 18, 2007 6:29 PM, Wolfgang Nádasi-Donner <ed.odanow@wonado.de> wrote:
>> Robert Dober wrote:
>>> ...wonder how this would scale if there were a Regexp#match allowing for an offset.
>>
>> ...which will come in Ruby 1.9:
>>
>> C:\Dokumente und Einstellungen\wolfgang>irb19
>> irb(main):001:0> "abcdef".match(/./,3)
>> => #<MatchData "d">
>>
> Great :)
> 
> I have written a 1.9 test and still lookahead is much better, I am
> surpprised as I got rid of all fancy stuff in the
> bf_sub method going back to my Regexp stuff happily again.

IMHO it is not surprising because the lookahead method uses one method 
(scan) which is implemented in C while you create a lot of temporary 
objects and also start scanning at *every* position in the string. 
Usually regexp engines are implemented much smarter than we can do in 
short method.  I am sure you have heard of Boyer Moore and Knuth Morris 
Pratt algorithms... :-)

>   def bf_sub substr
>     r = []
>     size.times do |i|
>       s =
>         substr.match(self,i)
>       r << ( s && s[0] )
>     end
>     r.compact
>   end

Kind regards

	robert