From: Nelson Owen <nowen@...55.com>
Date: 2005-09-08T05:17:55+09:00
Subject: Re: weird result when updating an array element

Simon Kr�ger wrote:

> 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
>
> .
>
Ah, I see now.  Thanks!