http://stackoverflow.com/a/22108497/793330

console-output.sh

$ irb

# sample array of slots
rbx-2.2.5 :001 > a = %w[slot1 slot3]
 => ["slot1", "slot3"] 

# require our class, in this case called section
rbx-2.2.5 :002 > require './lib/section.rb'
 => true 

# Now create a new Section Object with our slots above
rbx-2.2.5 :003 > s = Section.new slots: a
 => #<Section:0x48b0 @slots_mask=5> 
rbx-2.2.5 :004 > s.slots
 => ["slot1", "slot3"]

# what is the slots_mask as an Integer? 
rbx-2.2.5 :005 > s.slots_mask
 => 5 

# Now you can re-create any section with this slots_mask Integer value :)
rbx-2.2.5 :006 > s1 = Section.new slots_mask: 5
 => #<Section:0x4954 @slots_mask=5> 
rbx-2.2.5 :007 > s1.slots
 => ["slot1", "slot3"]

section.rb

class Section

  attr_accessor :slots, :slots_mask

  def initialize(opts = {})
    opts.each {|k,v| self.send "#{k}=", v}
  end

  # Note that the order of this array is essentially locked. You should only add to the end of it!
  SLOTS = %w(slot1 slot2 slot3 slot4)

  def slots=(slots)
    self.slots_mask = (slots & SLOTS).map {|r| 2**SLOTS.index(r)}.inject(:+)
  end

  def slots
    SLOTS.reject {|r| ((slots_mask || 0) & 2**SLOTS.index(r)).zero?}
  end

  def slot_symbols
    slots.map(&:to_sym)
  end

end