open_range

gistfile1.rb

class OpenEndedRange
  attr_reader :first, :last

  def initialize(first, last, exists = {})
    exists = { first => true, last => true }.merge(exists)
    @first, @last, @first_exists, @last_exists = first, last, exists[:first], exists[:last]
  end

  def first_exists?
    @first_exists 
  end

  def last_exists?
    @last_exists  
  end

  def include?(other)
    case [first_exists?, last_exists?]
    when [true,  true]
      first <=  other && other <=  last
    when [true,  false]
      first <= other
    when [false, true]
      other <= last
    when [false, false]
      true
    end
  end

  alias_method :===, :include?
end