class Date

Date.new(2007, 5, 12).change(year: 2005, month: 1) # => Date.new(2005, 1, 12)
Date.new(2007, 5, 12).change(day: 1) # => Date.new(2007, 5, 1)

The +options+ parameter is a hash with a combination of these keys: :year, :month, :day.
Returns a new Date where one or more of the elements have been changed according to the +options+ parameter.

def change(options)
  ::Date.new(
    options.fetch(:year, year),
    options.fetch(:month, month),
    options.fetch(:day, day)
  )
end