The difference in years between dates

difference_in_years.rb

# Year 2017

module Date
  # NOTE: There are two scenarios to consider based on the order of input dates:
  # 1. Ascending order: Only negative differences in days and/or months affect the year count.
  # 2. Descending order: Only positive differences in days and/or months affect the year count.  
  def self.difference_in_years(left_date, right_date)
    diff_in_years = right_date.year - left_date.year
    diff_in_months = (right_date.month - left_date.month) / 100.0
    diff_in_days = (right_date.day - left_date.day) / 10_000.0

    (diff_in_years + diff_in_months + diff_in_days).truncate
  end
end