# File lib/pathname.rb, line 527
  def relative_path_from(base_directory)
    if self.absolute? != base_directory.absolute?
      raise ArgumentError,
        "relative path between absolute and relative path: #{self.inspect}, #{base_directory.inspect}"
    end

    dest = []
    self.cleanpath.each_filename {|f|
      next if f == '.'
      dest << f
    }

    base = []
    base_directory.cleanpath.each_filename {|f|
      next if f == '.'
      base << f
    }

    while !base.empty? && !dest.empty? && base[0] == dest[0]
      base.shift
      dest.shift
    end

    if base.include? '..'
      raise ArgumentError, "base_directory has ..: #{base_directory.inspect}"
    end

    base.fill '..'
    relpath = base + dest
    if relpath.empty?
      Pathname.new(".")
    else
      Pathname.new(relpath.join('/'))
    end
  end