class DateTime

def localtime(utc_offset = nil)

Returns a Time instance of the simultaneous time in the system timezone. 
def localtime(utc_offset = nil)
  utc = new_offset(0)
  Time.utc(
    utc.year, utc.month, utc.day,
    utc.hour, utc.min, utc.sec + utc.sec_fraction
  ).getlocal(utc_offset)
end