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: cache.rb
    path of file: ./repos/opal/lib/opal
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require 'opal/paths'
require 'digest/sha2' unless RUBY_ENGINE == 'opal'

if RUBY_ENGINE != 
    
  def self.cache
    @cache ||=
      if RUBY_ENGINE == 'opal' || ENV['OPAL_CACHE_DISABLE'] || !Cache::FileCache.find_dir
        Cache::NullCache.new
      else
        Cache::FileCache.new
      end