From: Robert Klemme <shortcutter@...>
Date: 2008-12-03T19:20:06+09:00
Subject: Re: Question about op. overloading

2008/12/3 Maarten Mortier <maarten.mortier@gmail.com>:
> What about
> sudoku[r][c]= a
> though?
>
> Is that possible? I thought I'd be able to fluke it by overloading [] to
> return an array. But how do I pass parameters inside the bracket?

You do not need an array but rather a proxy:

class X
  ColProxy = Struct.new :owner, :column do
    def [](row)
      owner.matrix[[column, row]]
    end

    def []=(row,val)
      owner.matrix[[column, row]] = val
    end
  end

  attr_reader :matrix

  def initialize
    @matrix = {}
  end

  def [](column)
    ColProxy.new(self, column)
  end
end

irb(main):026:0> x = X.new
=> #<X:0x7ff5443c @matrix={}>
irb(main):027:0> x[1][2] = 3
=> 3
irb(main):028:0> x[1][2]
=> 3
irb(main):029:0> x
=> #<X:0x7ff5443c @matrix={[1, 2]=>3}>

> And how woudl I get
>
> puts sudoku[][3]
>
> to return the third column?

You can do it similarly.  Just make the argument for X#[] optional and
return another proxy.

I would really rather go with the other approach to stuff all
coordinates in a single pair of brackets and or provide additional
methods.

Kind regards

robert

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