concatenator.rb

class Concatenator
  def self.[](*objs)
    new(*objs)
  end

  def initialize(*objs)
    @objs = objs
  end

  def each(&blk)
    return to_enum unless block_given?
    eeach([*@objs], &blk)
  end

  private

  def eeach(objs, &blk)
    return if objs.empty?
    objs.shift.each(&blk)
    eeach(objs, &blk)
  end
end
__END__
c = Concatenator[[1, 2, 3], %w[1, 2, 3], %i[1 2 3], [1, 2, 3].each]
c.each # => Enumerator
c.each do |e|
  p e
end