From: Robert Klemme <shortcutter@...>
Date: 2009-11-20T01:17:50+09:00
Subject: Re: dynamic array?

2009/11/19 Marnen Laibow-Koser <marnen@marnen.org>:
> Freak Guard wrote:
>> I'd like to store 2d-data into an dynamic Array. The Matrix class got
>> the problem of being static sized and the other solution does not work:
>>
>> You can pass a block to Hash#new which gets called if the key does not
>> exist
>>
>>>> hsh = Hash.new {[]}
>> => {}
>>>> hsh[3]
>> => []
>>
>> But this does not seem to work with Arrays...
>>
>>>> ary = Array.new {[]}
>> => []
>>>> ary[2]
>> => nil
>>
>> Grettings
>> FreakGuard
>
> Hmmm...another approach:
>
> class DynamicArray < Hash
>  attr_reader :length
>
>  def initialize(length)
>    @length = length
>    super() {[]}
>  end
>
>  def []=(i, value)
>    super
>    @length = [i + 1, length].max
>  end
>
>  def to_a
>    (0..length).to_a.collect{|i| self[i]}
>  end
>
>  def each(&block)
>    self.to_a.each block
>  end
> end
>
> ...and delegate everything else to self.to_a.

What are you trying to achieve with this?  As far as I can see you are
mimicking Array behavior with a Hash.  So you have created a sparse
array but not a two dimensional array - which was what the OP wanted
if I understand him properly.

As a side note: I'd rather delegate to instead of inherit from Hash.
The DynamicArray is not a Hash.  For example, method #size remains in
the interface which might lead to surprises.

Kind regards

robert


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