inspect

# File activesupport/lib/active_support/duration.rb, line 113
    def inspect #:nodoc:
      parts.
        reduce(::Hash.new(0)) { |h,(l,r)| h[l] += r; h }.
        sort_by {|unit,  _ | [:years, :months, :days, :minutes, :seconds].index(unit)}.
        map     {|unit, val| "#{val} #{val == 1 ? unit.to_s.chop : unit.to_s}"}.
        to_sentence(locale: ::I18n.default_locale)
    end