Question

class CartesianProduct
include Enumerable
# your code here
end
#Examples of use
c = CartesianProduct.new([:a,:b], [4,5])
c.each { |elt| puts elt.inspect }
# [:a, 4]
# [:a, 5]
# [:b, 4]
# [:b, 5]
c = CartesianProduct.new([:a,:b], [])
c.each { |elt| puts elt.inspect }
# (nothing printed since Cartesian product
# of anything with an empty collection is empty)

I am new to ruby. And I understand how to define a instance method of Cartesian Product, but I have no clue to this. How should I construct the class object to fulfill the requirement.

Answer 1

I wouldn’t use a class for that, but keeping the structure of the question, I’d write:

class CartesianProduct
  include Enumerable

  def initialize(xs, ys)
    @xs = xs
    @ys = ys
  end

  def each
    return to_enum unless block_given?
    @xs.each do |x| 
      @ys.each { |y| yield [x, y] }
    end
  end
end

Instead, I’d simply write xs.product(ys) or build my own Array#lazy_product if laziness were important (see this ticket).