From: Reinder Verlinde <reinder@...>
Date: 2005-12-17T08:12:46+09:00
Subject: Re: challenge - regex which matches nothing

In article <Pine.LNX.4.62.0512161503470.24863@harp.ngdc.noaa.gov>,
 ara.t.howard@noaa.gov wrote:

> On Sat, 17 Dec 2005, James Edward Gray II wrote:
> 
> > On Dec 16, 2005, at 3:47 PM, mathew wrote:
> >
> >> ara.t.howard@noaa.gov wrote:
> >>> comments?
> >> 
> >> I think you mean 'a regex which doesn't match anything'; surely
> >> /^$/ is a regex which matches nothing?
> >
> > No, he meant a regex that always fails.
> 
> lol!
> 
> ok.  before this gets out of hand, what i meant was
> 
>    regex =~ any_possible_string #=> false
> 
<nitpick>That never happens in Ruby. =~ returns nil if the expression 
and the string passed to it do not match.</nitpick>

I would guess that it should be possible to put all possible characters 
between [ and ], and negate that.

I think /\z\a/ should do the trick, too (from experimentation, I can not 
find anything that matches it, but maybe I haven't thought/experimented 
enough about/with it)

Finally, I think one can to build a not-too-long regex that only matches 
strings of length larger than addressable memory, using something like:

/((x{1000000000}){1000000000}){1000000000}/

If you repeat that pattern a couple of times you get a regular 
expression that, for all practical purposes, will match nothing.

Reinder