From: Rob Biedenharn <Rob@...>
Date: 2008-06-05T08:42:00+09:00
Subject: Re: double assignation in a hash

On Jun 4, 2008, at 7:23 PM, nico Itkin wrote:

> hi !
>
> I'm new to ruby, i'd like to know if it is possible to make the
> following kind of assignation in a hash, like i used to do in php :
>
> a={}
> a[:b][:c]="value"
>
> the goal for me is to create a hash by iterating on keys, like
>
> hash={}
> [a,b,c].each do |k1|
>  [d,e,f].each do |k2|
>    hash[k1][k2] = afunction(k1,k2)
>  end
> end
>
> this last code lead to a nil.[] error
>
> Could you help me ? .


Your problem is that a[:b] is not a hash.  You can get this effect by  
defining a default for the hash 'a' like so:

irb> a = Hash.new {|h,k| h[k] = {} }
=> {}
irb> a[:b][:c] = 'value'
=> "value"
irb> a
=> {:b=>{:c=>"value"}}

The block supplied to Hash.new is called with the hash and the key  
when the key doesn't exist. So the effect is as if you had:

a = {}
a[:b] = {}
a[:b][:c] = 'value'

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com