From: Leslie Viljoen <leslieviljoen@...>
Date: 2008-02-21T00:06:39+09:00
Subject: Re: ||= [] idiom

On Feb 20, 2008 12:26 AM, MenTaLguY <mental@rydia.net> wrote:
> 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.
>
> -mental


Doesn't seem to work though:

irb(main):030:0> k=Hash.new{Array.new}
=> {}
irb(main):031:0> k
=> {}
irb(main):032:0> k[1] << 1
=> [1]
irb(main):033:0> k[1] << 1
=> [1]
irb(main):034:0> k[1] << 1
=> [1]
irb(main):035:0> k[1] << 1
=> [1]
irb(main):036:0> k
=> {}
irb(main):037:0> k[1]
=> []

This works:
irb(main):038:0> h = Hash.new{|h, k| h[k] = []}
=> {}
irb(main):039:0> h[1] << 1
=> [1]
irb(main):040:0> h[1] << 1
=> [1, 1]
irb(main):041:0> h[1] << 1
=> [1, 1, 1]
irb(main):042:0> h
=> {1=>[1, 1, 1]}
irb(main):043:0> h[1] << 2
=> [1, 1, 1, 2]
irb(main):044:0> h[2] << 2
=> [2]
irb(main):045:0> h[2] << 2
=> [2, 2]
irb(main):046:0> h
=> {1=>[1, 1, 1, 2], 2=>[2, 2]}

Great!