# File lib/mongo/collection.rb, line 534
    def create_index(spec, opts={})
      opts[:dropDups] = opts[:drop_dups] if opts[:drop_dups]
      field_spec      = parse_index_spec(spec)
      opts            = opts.dup
      name            = opts.delete(:name) || generate_index_name(field_spec)
      name            = name.to_s if name
      generate_indexes(field_spec, name, opts)
      name
    end