From: Michael Fellinger <m.fellinger@...>
Date: 2008-02-24T14:33:58+09:00
Subject: Re: [Q] difference between StringScanner#scan and Regexp#match

On Sun, Feb 24, 2008 at 1:20 PM, makoto kuwata <kwa@kuwata-lab.com> wrote:
> Hi,
>
>  I'm planning to implement StringScanner in pure Ruby.
>  But I found that it is hard to implement StringScanner#scan()
>  in pure Ruby, because of the difference between Regexp#match()
>  and StringScanner#scan().
>
>  StringScanner#scan() matches only when pattern matches at the
>  beginning (or at the current position) of input string.
>
>   require 'strscan'
>   input = 'foo 123'
>   scanner = StringScanner.new(input)
>   p scanner.scan(/\d+/)   #=> nil
>
>  But Regexp#match() matches whenever input string contains pattern.
>
>   input = 'foo 123'
>   m = /\d+/.match(input)
>   p m[0] if m  #=> "123"
>
>
>  Is it possible to restrict Regexp#match() to match only when
>  pattern starts at the beginning of input string?
>  My idea is to convert /regexp/ into /\A(?:regexp)/ every time,
>  but it is a litte ugly.
>  Is there any good idea to emulate StringScanner#scan in pure Ruby?

input = 'foo 123'
if (input =~ /\d+/) == 0
  p $& # doesn't happen
end