From: Tim Pease <tim.pease@...>
Date: 2007-08-21T00:13:05+09:00
Subject: Re: How to implement a hash whose key is another hash?

On 8/20/07, acmeman1@yahoo.com <acmeman1@yahoo.com> wrote:
> I understand that the key of a hash can be any object. Therefore,
> I would think that the key of a hash can be another hash.  If I have
> the following code sequence. (I using ruby 1.8.5 (2006-08-25) [i486-
> linux])
>
>
> require 'pp'
> test ={}
> test["new"=>"girl"]= 100
> test["new"=>"girl"]= 200
> pp test
>
> I am expecting the output to be
>
> {{"new"=>"girl"}=>200}
>
> However the output I am getting is
>
> {{"new"=>"girl"}=>100,
>  {"new"=>"girl"}=>200}
>

The problem is that you are not using the same key ...

k = {'new' => 'girl'}
k.hash       #=> 1072992710

h = {}
h[k] = 100
h[k] = 200
p h           #=> {{"new" => "girl"} => 200}

k = {'new' => 'girl'}
k.hash      #=> 1072934850

h[k] = 300
p h          #=> {{"new"=>"girl"}=>300, {"new"=>"girl"}=>200}


To use an object as a hash key, you need to implement a "hash" method
that returns the same value when the contents of the hash are the
same. But this gets tricky.

Blessings,
TwP