From: Gregory Seidman <gsslist+ruby@...>
Date: 2008-02-20T10:55:45+09:00
Subject: Re: IP Address to Decimal - is an one-liner possible?

On Wed, Feb 20, 2008 at 10:38:36AM +0900, Tiago Pinto wrote:
> A friend of mine needs to convert a string containing an IP Address
> (such as "127.0.0.1") to a decimal (that example would translate to
> 2130706433, <http://www.allredroster.com/iptodec.htm> said).
> 
> We got a solution (that can easily be written in 2 lines):
> 
> ip_d = 0 # let's start with zero
> ip_s = "127.0.0.1" # this our ip address as a string
> ip_a = ip_s.split(".") # now it's an array
> ip_i = ip_a.map{|i| i.to_i} # an array of ints
> ip_i.reverse! # let's reverse so we can use the array's indexes as the
> exponents when translating from base 256 to base 10)
> ip_i.each_with_index{|e,i| ip_d += e*(256**i)} # this is pure math,
> we're just changing bases here
> 
> Our challenge (between me and my friend) was getting an one-liner for
> this. I think it'd be easy with something like Array#map_with_index or
> Array#inject_with_index because we use the indexes, here.
> 
> What do you think? There's a way to do this? Is this just a silly question?
> 
> I know, we should be working, but we both love Ruby.

ip_s.split('.').inject(0) { |t,v| v.to_i + t*256 }

> Best,
> Tiago
--Greg