You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: index.rb
    path of file: ./repos/stackneveroverflow/vendor/bundle/ruby/2.3.0/gems/rugged-0.26.0b5/lib/rugged
    
    the code of the file until where you have to start completion: # Copyright (C) the Rugged contributors.  All rights reserved.
#
# This file is part of Rugged, distributed under the MIT license.
# For full terms see the included LICENSE file.

module Rugged
  class Index
    include Enumerable


    # call-seq:
    #   index.diff([opti
    
    def diff(*args)
      options = args.last.is_a?(Hash) ? args.pop : {}
      other   = args.shift

      case other
      when nil
        diff_index_to_workdir options
      when ::Rugged::Commit
        diff_tree_to_index other.tree, options
      when ::Rugged::Tree
        diff_tree_to_index other, options
      else
        raise TypeError, "A Rugged::Commit or Rugged::Tree instance is required"
      end