each_slice.rb

module Enumerable
  def i_each_slice(n, &block)
    raise "invalid slice size" if n <= 0

    i, ary = 0, []

    each do |a|
      ary << a
      i += 1
      if i >= n
        yield ary
        i, ary = 0, []
      end
    end

    yield ary if i > 0
  end
end

(1..10).i_each_slice(3) { |a| p a }