class DateTime

def advance(options)

:minutes, :seconds.
:months, :weeks, :days, :hours,
The +options+ parameter takes a hash with any of these keys: :years,
Uses Date to provide precise Time calculations for years, months, and days. 
def advance(options)
  d = to_date.advance(options)
  datetime_advanced_by_date = change(:year => d.year, :month => d.month, :day => d.day)
  seconds_to_advance = \
    options.fetch(:seconds, 0) +
    options.fetch(:minutes, 0) * 60 +
    options.fetch(:hours, 0) * 3600
  if seconds_to_advance.zero?
    datetime_advanced_by_date
  else
    datetime_advanced_by_date.since seconds_to_advance
  end
end