Re: Extensions to ipaddr.rb

On Thu, Mar 22, 2007 at 03:58:51PM +0900, Brian Candler wrote:
[snip]
> > class IPAddr
> >   def entries
> >     list = []
> >     0.upto(~@mask_addr & IN4MASK) do |i|
> >       list << IPAddr.new(_to_string(@addr + i))
> >     end
> >     list
> >   end
> > end
> > 
> > ip = IPAddr.new("192.168.5.0/28")
> > ip.entries.each do |ip|
> >   puts ip
> > end
> 
> I would do it differently; give class IPAddr an 'each' method which yields
> each of the values (perhaps delegating to Range#each), and then make it
> Enumerable.

Agreed. This was just a 5 minute hack to demonstrate the idea. This capability
is currently lacking entirely and would be very useful (at least to me).

> Otherwise, if you call 'entries' on a /48 IPv6 address you will generate an
> intermediate array with 2^80 entries :-(
 
Yeah. A generator-based approach is better as no intermediate Array is
created.

> Now, arguably a Range might be better internal data structure than an address
> plus mask, as both 'include?' and 'size' would be trivial. You could then do
>    IPAddr.new("192.168.0.5", "192.168.0.13")
> which might be useful. You could even subclass Range.
> 
> But I wasn't coming here to suggest a redesign of IPAddr - it works, and it
> does *almost* what I want already. However, given a (say) /28 prefix, I need
> to be able to find:
> 
>   - the base address + 1 (router IP)
>   - the base address + 2 (dhcp start)
>   - the end of the block - 2 (dhcp end)
>   - the end of the block - 1 (broadcast)
>   - the netmask
> 
> That's why I proposed those new methods, as there doesn't seem to be a
> straightforward way to do it otherwise without digging directly in with
> instance_eval.
 
Indeed. Hopefully this will make it into ipaddr.rb in some form.

-- 
Jos Backus
jos at catnook.com