From: ara.t.howard@...
Date: 2006-10-27T04:29:36+09:00
Subject: Re: Beginner would like help with oo-modelling

On Fri, 27 Oct 2006, Pa Per wrote:

> Ok, now I understand what you mean. And you are right, for some reason I
> totally got off the path I was following initially.  But the problem I'm
> trying to deal with right now would probably persist when storing the
> information inside an object:
>
> I'm currently using the num.step method to iterate from zero to the length
> of the ruler, in order to calculate the positions. This creates multiple
> types of lines on the same position, e.g.
>
> |         |         |           lines[0]
> |    |    |    |    |    |      lines[1]
> ||||||||||||||||||||||||||||    lines[2]
> 0    5   10
>
> lines indicate value, e.g. lines[2] = [1..n]
>
> To prevent that, when adding a line (position) to lines, it is necessary to
> iterate over the previous array(s), checking if the value-to-be is already
> included (enum.include?).
>
> I don't like that approach, although it probably works. I have yet to
> experiment with "following the metaphor".
>
> Alternatively, I would have to find a method to generate the positions
> directly, like
> 0, 10, 20, 30
> 5, 15, 25, 35
> 1,2,3,4,6,7,8,9, ...
>
> But since the pattern depends on the parameter, I am not sure if a
> reasonably short equation could be found.

it's quite short:

     harp:~ > cat a.rb
     class TickGen
       include Enumerable
       def initialize a, step, b = nil
         @a, @step, @b = a, step, b
       end
       def each
         n = @a
         loop{
           yield n
           n += @step
           break if @b and n > @b
         }
       end
       def include? tick
         q, r = (tick - @a).divmod @step
         r.zero? and (@b.nil? or q <= @b)   #=> THE EQUATION
       end
       def to_a
         raise "infinitly big array" unless @b
         super
       end
       def to_ary() to_a end
       def | other
         (to_a | other.to_a).sort.uniq
       end
     end

     a = TickGen.new 0, 2, 10
     p a.to_a
     p a.include?(8)

     b = TickGen.new 1, 1, 10
     p b.to_a
     p b.include?(8)

     c = TickGen.new 1, 2, 10
     p c.to_a
     p c.include?(8)

     p( a | b | c )


     harp:~ > ruby a.rb
     [0, 2, 4, 6, 8, 10]
     true
     [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
     true
     [1, 3, 5, 7, 9]
     false
     [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

regards.

-a
-- 
my religion is very simple.  my religion is kindness. -- the dalai lama