```ruby
require 'active_support/backtrace_cleaner'

module Rails
  class BacktraceCleaner < ActiveSupport::BacktraceCleaner
    APP_DIRS_PATTERN = /^\/?(app|config|lib|test)/
    RENDER_TEMPLATE_PATTERN = /:in `_render_template_\w*'/

    def initialize
      super
      add_filter   { |line| line.sub("#{Rails.root}/", '') }
      add_filter   { |line| line.sub(RENDER_TEMPLATE_PATTERN, '') }
      add_filter   { |line| line.sub('./', '/') } # for tests

      add_gem_filters
      add_silencer { |line| line !~ APP_DIRS_PATTERN }
    end

    private
      def add_gem_filters
        gems_paths = (Gem.path | [Gem.default_dir]).map { |p| Regexp.escape(p) }
        return if gems_paths.empty?

        gems_regexp = %r{(#{gems_paths.join('|')})/gems/([^/]+)-([\w.]+)/(.*)}
        add_filter { |line| line.sub(gems_regexp, '\2 (\3) \4') }
      end
  end
end
```

Move object allocation out of loop
user
```ruby
require 'active_support/backtrace_cleaner'

module Rails
  class BacktraceCleaner < ActiveSupport::BacktraceCleaner
    APP_DIRS_PATTERN = /^\/?(app|config|lib|test)/
    RENDER_TEMPLATE_PATTERN = /:in `_render_template_\w*'/
    EMPTY_STRING = ''.freeze
    SLASH        = '/'.freeze
    DOT_SLASH    = './'.freeze

    def initialize
      super
      @root = "#{Rails.root}/".freeze
      add_filter { |line| line.sub(@root, EMPTY_STRING) }
      add_filter { |line| line.sub(RENDER_TEMPLATE_PATTERN, EMPTY_STRING) }
      add_filter { |line| line.sub(DOT_SLASH, SLASH) } # for tests

      add_gem_filters
      add_silencer { |line| line !~ APP_DIRS_PATTERN }
    end

    private
      def add_gem_filters
        gems_paths = (Gem.path | [Gem.default_dir]).map { |p| Regexp.escape(p) }
        return if gems_paths.empty?

        gems_regexp = %r{(#{gems_paths.join('|')})/gems/([^/]+)-([\w.]+)/(.*)}
        gems_result = '\2 (\3) \4'.freeze
        add_filter { |line| line.sub(gems_regexp, gems_result) }
      end
  end
end
```
assistant