From: Dave Howell <groups.2009a@...>
Date: 2010-07-15T18:23:00+09:00
Subject: Re: Return nothing when looking outside the bounds of 2D array?

I was going to suggest using the 'case' statement instead of all those elsifs, but then I realized there was an even better way. 

class Array2D

	Delta=[[0,0], [0,1], [1,1], [1,0], [1,-1], [0,-1], [-1,-1], [-1,0], [-1,1]]
	attr_reader :width, :height

	def initialize(width, height)
		@width = width
		@height = height
		@data = Array.new(@width) { Array.new(@height) }
	end

	def [](x, y, z)
		deltaX, deltaY = *Delta[z]
		x = x + deltaX % @width 
		y = y + deltaY
		@data[x][y] unless y<0 or y>@height 
	end
	
	def []=(x, y, z, value)
		deltaX, deltaY = *Delta[z]
		x = (x + deltaX) % @width # modulus % allows wrapping
		y = y + deltaY
		@data[x][y] = value unless y<0 or y>(@height-1)
	end
end


Obviously the Delta array takes the place of the elsif chains in both [] and []=. Also, :width and :height are defined with attr_reader, not attr_accessor, since it doesn't do any good at all to change those values after the array has been created.