real_join.rb

class Array
  # Note: Could also be called ary_join.
  #
  def real_join element
    combined = [element]*(size-1)
    zip(combined).flatten.compact
  end
end

p [1,2,3,4].real_join 'and' #=> [1, 'and', 2, 'and', 3, 'and', 4]