define fixed options for fields in a rails way

gistfile1.rb

class Task < ActiveRecord::Base

  # get an array with 0.0, 0.25, 0.50, 0.75, ...
  @@hours_options = 0.step(3, 0.25).collect {|x| x}

  belongs_to :proyect

  # valudation rules
  validates :hours, :inclusion => { :in => @@hours_options }

  # helper to get hours options
  def self.get_hours_options
       @@hours_options.map{ |z| [z,z]}
   end
end