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: weakidconv.rb
    path of file: ./repos/artichoke/artichoke-backend/vendor/ruby/lib/drb
    
    the code of the file until where you have to start completion: # frozen_string_literal: false
require_relative 'drb'
require 'monitor'

modul
    
      def fetch(ref)
        synchronize do
          @immutable.fetch(ref) {
            @map.each { |key, _|
              return key if key.__id__ == ref
            }
            raise RangeError.new("invalid reference")
          }
        end
      end