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: formula_creator.rb
    path of file: ./repos/brew/Library/Homebrew
    
    the code of the file until where you have to start completion: require "digest"
require "erb"

module Homebrew
  class FormulaCreator
    attr_reader :url, :sha256, :desc, :
    
    def generate!
      raise "#{path} already exists" if path.exist?

      if version.nil? || version.null?
        opoo "Version cannot be determined from URL."
        puts "You'll need to add an explicit 'version' to the formula."
      elsif fetch?
        unless head?
          r = Resource.new
          r.url(url)
          r.version(version)
          r.owner = self
          @sha256 = r.fetch.sha256 if r.download_strategy == CurlDownloadStrategy
        end