From: Robert Klemme <shortcutter@...>
Date: 2009-11-19T23:02:14+09:00
Subject: Re: dynamic array?

2009/11/19 Freak Guard <freakguard@gmail.com>:
> 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

So basically you need a lazy Matrix?  Or do you need a matrix which
accepts arbitrary indexes?

In 1.8.7 and newer this is as easy as

class LazyM
  def initialize(default = nil)
    @h = Hash.new(default)
  end

  def [](x,y)
    @h[[x,y]]
  end

  def []=(x,y,z)
    @h[[x,y]]=z
  end

  def clear
    @h.clear
  end
end

Kind regards

robert


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