A module and a class to deal with birthday

birthday.rb

require "date"

module Birthday
  def birthday(year_of_birthday = Date.today.year)
    if birthdate.leap?
      year_of_birthday += 1 until Date.new(year_of_birthday).leap?
    end

    Date.new(year_of_birthday, birthdate.month, birthdate.day)
  end

  def birthday?(other_date = Date.today)
    other_date.month == birthdate.month && other_date.day == birthdate.day
  end

  def years_from(other_date)
    ((other_date - birthdate).to_i / 365.2422).floor
  end

  def years_old
    years_from Date.today
  end

  def next_birthday(other_date = Date.today)
    birthday other_date.year + (before_birthday?(other_date) ? 0 : 1)
  end

  def previous_birthday(other_date = Date.today)
    birthday other_date.year + (after_birthday?(other_date) ? 0 : -1)
  end

  def before_birthday?(other_date = Date.today)
    other_date < birthday(other_date.year)
  end

  def after_birthday?(other_date = Date.today)
    other_date > birthday(other_date.year)
  end

  def centenarian?(other_date = Date.today)
    years_from(other_date) >= 100
  end

  def newborn?(other_date = Date.today)
    years_from(other_date) == 0
  end
end

# Examples
#
#   puts Birthdate.parse("02 nov 1986").next_birthday
#   # >> 2012-11-02
class Birthdate < Date
  include Birthday

  def birthdate
    self
  end
end