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: layout.rb
    path of file: ./repos/genometools/gtruby/annotationsketch
    
    the code of the file until where you have to start completion: #
# Copyright (c) 2008 Sascha Steinbiss <steinbiss@zbh.uni-hamburg.de>
# Copyright (c) 2008 C
    
    def set_track_ordering_func(proc)
      @tof = DL.callback('ISSP') do |s1, s2, data_ptr|
               r = proc.call(s1, s2)
               if (!r.is_a?(Numeric)) then
                 GT::gterror("Track ordering callback must return a number!")
               end
               r.to_i
             end