method
sum
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sum(sign, time = ::Time.current)
protected
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# File activesupport/lib/active_support/duration.rb, line 90 def sum(sign, time = ::Time.current) #:nodoc: parts.inject(time) do |t,(type,number)| if t.acts_like?(:time) || t.acts_like?(:date) if type == :seconds t.since(sign * number) else t.advance(type => sign * number) end else raise ::ArgumentError, "expected a time or date, got #{time.inspect}" end end end