From: Robert Klemme <bob.news@...>
Date: 2003-09-12T23:17:11+09:00
Subject: Re: OO Challenge


"Robert Feldt" <feldt@ce.chalmers.se> schrieb im Newsbeitrag
news:oprvd068apoglyup@mail1.telia.com...
[snip]

I prefer this approach since it is more OO in the sense that rules and
their names are better bound together.

    robert


require 'set'

# abstract base, not really needed
class TaxGroup
  class << self
    attr_reader :all_groups

    def inherited(gr)
      $stderr.puts "Group #{gr}"
      ( @all_groups ||= Set.new ) << gr
    end
  end
end

# tax groups
class TaxGroupSoldier < TaxGroup
  def calc_tax(emp)
    emp.salary/10.0
  end
end

class TaxGroupProf < TaxGroup
  def calc_tax(emp)
    emp.salary/15.0+100
  end
end

# tax payers
class TaxPayer
  attr_reader   :tax_groups
  attr_accessor :salary

  def initialize(sal, groups = [])
    @salary = sal
    @tax_groups = Set.new
    @tax_groups.merge groups
  end

  def tax()
    self.tax_groups.map do |gr|
      gr.new.calc_tax(self)
    end.max
  end
end

# example
taxPayers = [
        TaxPayer.new(3000,[TaxGroupSoldier]),
        TaxPayer.new(5000,[TaxGroupProf]),
        TaxPayer.new(6000,[TaxGroupProf, TaxGroupSoldier]),
]

taxPayers.each do |p|
  puts "#{p.inspect}: #{p.tax}"
end