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: mmc3.rb
    path of file: ./repos/truffleruby/bench/optcarrot/lib/optcarrot/mapper
    
    the code of the file until where you have to start completion: module Optcarrot
  # MMC3 mapper: http://wiki.nesdev.com/w/index.php/MMC3
  class MMC3 < ROM
    MAPPER_DB[0x04] = self

    def init(rev = :B) # rev = :A or :B or :C
 
    
    def init(rev = :B) # rev = :A or :B or :C
      @persistant = rev != :A

      @prg_banks = @prg_banks.flatten.each_slice(0x2000).to_a
      @prg_bank_swap = false

      @chr_banks = @chr_banks.flatten.each_slice(0x0400).to_a
      @chr_bank_mapping = [nil] * 8
      @chr_bank_swap = false
    end