From: "Simon Kröger" <SimonKroeger@...>
Date: 2005-09-08T04:54:28+09:00
Subject: Re: weird result when updating an array element

Nelson Owen wrote:
> Given the code below, only one element in @ver should be changed, 
> however when I execute the code all the elements are changed. Can anyone 
> explain why this is happening?
> 
> class SomeClass
>    def initialize
>        @ver  = Array.new(2, {'pos' => Array.new(3), 'col' => Array.new(4)})
>        @ver[0]['pos'][0] = 0
>        puts @ver.inspect
>    end
> end
> SomeClass.new
> 
> actual result:
> [{"col"=>[nil, nil, nil, nil], "pos"=>[0, nil, nil]}, {"col"=>[nil, nil, 
> nil, nil], "pos"=>[0, nil, nil]}]
> 
> expected result:
> [{"col"=>[nil, nil, nil, nil], "pos"=>[0, nil, nil]}, {"col"=>[nil, nil, 
> nil, nil], "pos"=>[nil, nil, nil]}]
> 
> 

from the Array docs:

...it is created with size copies of obj (that is, size references to 
the same obj).

So ver[0] and ver[1] are in fact pointing to the same object.

You can use:

@ver  = Array.new(2) {{'pos' => Array.new(3), 'col' => Array.new(4)}}

wich looks odd, but works :)

cheers

Simon