properties.rb

#!/usr/bin/env ruby

properties = []

class Property

  def initialize(number, postcode)
    @number, @postcode = number, postcode
    @vacant = false
  end

  def vacant?
    @vacant
  end

  def vacant=(val)
    @vacant = val
  end

end

class CommercialProperty < Property

  BUSINESS_RATE_PER_FOOT = 10

  def initialize(number, postcode, square_footage)
    super(number, postcode)
    @square_footage = square_footage
  end


  def business_rates
    @square_footage * BUSINESS_RATE_PER_FOOT
  end

  def tax
    business_rates
  end

end

class ResidentialProperty < Property

  BAND_RATES = {
    :a => 100,
    :b => 200,
    :c => 300
  }

  def initialize(number, postcode, no_of_people, band)
    super(number, postcode)
    self.vacant = no_of_people == 0 # self.vacant=(no_of_people == 0)
    @no_of_people, @band = no_of_people, band
  end

  def council_tax
    @no_of_people * BAND_RATES[@band]
  end

  def tax
    return 0 if vacant?
    council_tax
  end

end

epworth_house = CommercialProperty.new(25, "EC1Y 1AA", 50000)
flat = ResidentialProperty.new(1, "EC1Y 1AA", 0, :b)
# flat.no_of_people = 2
# flat.vacant = true

properties << epworth_house # properties.push(epworth_house)
properties << flat

# calculates cumulative tax from all properties
overall_tax = properties.inject(0) {|memo, property| memo += property.tax; memo}

puts "We have #{properties.length} property, paying #{overall_tax} in taxes"