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: client.rb
    path of file: ./repos/cryptoexchange/lib/cryptoexchange
    
    the code of the file until where you have to start completion: module Cryptoexchange
  class Client
    def initialize
    end

    def cache
      Cryptoexchange::Cache.ticker_cache
    end

    
    
    def order_book_stream(market_pair:, onopen: nil, onmessage:, onclose: nil)
      fetch_stream(
        market_pair: market_pair,
        onopen: onopen,
        onmessage: onmessage,
        onclose: onclose,
        stream_type: 'order_book'
      )
    end