# File lib/diffy/diff.rb, line 35
    def initialize(string1, string2, options = {})
      @options = self.class.default_options.merge(options)
      if ! ['strings', 'files'].include?(@options[:source])
        raise ArgumentError, "Invalid :source option #{@options[:source].inspect}. Supported options are 'strings' and 'files'."
      end
      @string1, @string2 = string1, string2
    end