tally_bag.rb

class TallyBag
  include Enumerable

  def initialize
    @tallys = Hash.new{0}
  end

  def each
    if block_given?
      @tallys.each(&Proc.new)
    else
      @tallys.each
    end
  end

  def []=(obj, tally)
    @tallys[obj] = tally
  end

  def [](obj)
    @tallys[obj]
  end

  def <<(obj)
    @tallys[obj] += 1
  end
end

usage_reporter.rb

class UsageReporter
  def initialize(files = Dir['**/*.rb'])
    @files = files
    @methods = Set.new
    @total_number_of_calls = TallyBag.new
    @file_number_of_calls = Hash.new{TallyBag.new}
  end

  def report
    @files.each do |file|
      extract_methods(file) do |body, method|
        @file_number_of_calls[file][method] += body.scan(/\b#{method}\b/).size
        @methods << method
      end
    end

    @files.each do |file|
      @methods.each do |method|
        body = File.read(file)
        @total_number_of_calls[method] += body.scan(/\b#{method}\b/).size
      end
    end

    puts "Possibly uncalled methods"
    @total_number_of_calls.each do |method, tally|
      puts "- #{method}" if tally == 1
    end

    puts "Possibly private methods"
    puts
    @file_number_of_calls.each do |file, method_tallys|
      puts "#{file}"
      method_tallys.each do |method, tally|
        puts "- #{method}" if @total_number_of_calls[method] == tally
      end
      puts
    end
  end

  def extract_methods(file)
    body = File.read(file)
    methods = body.scan(/def\s+(?:\w+\.)?(\w+)/).flatten
    methods.each do |method|
      yield body, method
    end
  end
end

UsageReporter.new.report