# File lib/jcode.rb, line 133
  def tr!(from, to)
    return nil if from == ""
    return self.delete!(from) if to == ""

    pattern = TrPatternCache[from] ||= /[#{_regex_quote(from)}]/
    if from[0] == ?^
      last = /.$/.match(to)[0]
      self.gsub!(pattern, last)
    else
      h = HashCache[from + "1-0" + to] ||= expand_ch_hash(from, to)
      self.gsub!(pattern) do |c| h[c] end
    end
  end