inspect

# File activesupport/lib/active_support/duration.rb, line 370
    def inspect #:nodoc:
      parts.
        reduce(::Hash.new(0)) { |h, (l, r)| h[l] += r; h }.
        sort_by { |unit,  _ | PARTS.index(unit) }.
        map     { |unit, val| "#{val} #{val == 1 ? unit.to_s.chop : unit.to_s}" }.
        to_sentence(locale: ::I18n.default_locale)
    end