filter_by

# File railties/lib/rails/paths.rb, line 65
      def filter_by(constraint)
        all = []
        all_paths.each do |path|
          if path.send(constraint)
            paths  = path.paths
            paths -= path.children.values.map { |p| p.send(constraint) ? [] : p.paths }.flatten
            all.concat(paths)
          end
        end
        all.uniq!
        all.reject! { |p| !File.exists?(p) }
        all
      end