From: Brian Schroeder <spam0504@...>
Date: 2004-09-23T08:14:34+09:00
Subject: Re: Newbie: Case statement

On Wed, 22 Sep 2004 23:33:52 +0100, Graham Foster wrote:

> As a newbie I'm confused about the Case construct. All the documentation
> I've found states "case operates by comparing the target with EACH of
> the expressions after the When keyword" This does NOT appear to happen,
> as only the first match is ever actioned, so overlapping WHEN cases are
> skipped. def test(x)
>     case x
>         when 1..2
>             print "In A\n"
>         when 1..3
>             print "In B\n"
>         when 2..4
>             print "In C\n"
>     end
> end
> test(2)
> only outputs "In A"
> I assume this is expected behaviour? (I'm ex-C - and was looking for
> fall-through behaviour)
> So my underlying question is:- what's the fastest Ruby for checking
> which of the 8 possible adjacent cells on a board (2D array) are still
> "on the board"
> Thx
> Graham

Hello Graham,

what exactly do you want to know? Do you want to test for each cell if it
is on the board,

  def in_board(x, y)
    (0 <= x) and (x < @width) and (0 <= y) and (y < @height)
  end

or do you want to do something based on the position on the board, in
which case the fastest (if not most concise ruby) I can come up with at
this hour of the night would be:

  def position(x, y)
    return :off_board if (x < 0) or (y < 0) or (@width <= y) or (@height
    <= y) if (x == 0)
      if (y == 0)
        return :top_left
      elsif (y == @height - 1)
        return :bottom_left
      else
        return :left
      end
    elsif (x == @width - 1)
      if (y == 0)
        return :top_right
      elsif (y == @height - 1)
        return :bottom_right
      end
    else
      return :not_at_border
    end
  end

But this is not very concise. It is depending on what you want to do?

If you have a two dimensional array, you will get in any case nil values
for off-board positions, so maybe

class Board
  attr_reader :width, :height
  
  def initialize(width, height)
    @width = width; @height = height
    @array = Array.new(width) { Array.new(height) { :empty } }
  end

  def [](x, y)
    return nil if (x < 0) or (y < 0)
    return @array[x][y]
  end
end

will be enough for you, because it returns nil for each cell that is off
board.

regards,

Brian

Disclaimer: I consider myself also a nuby, so don't take anything for
granted I'm proposing.

-- 
Brian Schr旦der
http://www.brian-schroeder.de/