From: Leslie Viljoen <leslieviljoen@...>
Date: 2008-02-21T00:56:52+09:00
Subject: Re: ||= [] idiom

On Feb 20, 2008 11:44 AM, Robert Klemme <shortcutter@googlemail.com> wrote:
> 2008/2/19, MenTaLguY <mental@rydia.net>:
>
> > On Wed, 20 Feb 2008 07:15:52 +0900, Sebastian Hungerecker <sepp2k@googlemail.com> wrote:
> > >> .. is there a better way?
> > >
> > > @categories = Hash.new {Array.new}
> > > pagelist.each do |resource|
> > >   @categories[resource.tag] << resource
> > > end
> >
> > Although it is specific to hashes, when this is applicable I do
> > think it can be a better approach than the more general approach
> > I outlined in my other email.
>
> But it needs the fix Joel pointed out:
>
> @categories = Hash.new {|h,k| h[k] = []}
>
> Theoretically this could even be more efficient than
>
> (@categories[k] ||= []) << v
>
> because the check is done only once per missing key.

A benchmark does indeed show it to be faster, though you need truly huge arrays
to see the difference.