Reduce Duration#inspect to a single series of transformations

* eliminates need for temp Hash

Also added a couple of examples to DurationTest to specify:

* duration can be defined with units out of order e.g.
  1.month + 1.year + 1.second + 1.day
* equality with a Fixnum works regardless of which operand is on which
  side of the operator

1 files changed, 4 insertions, 6 deletions

diff --git a/activesupport/lib/active_support/duration.rb b/activesupport/lib/active_support/duration.rb
index 00727ef73c..87b6407038 100644
--- a/activesupport/lib/active_support/duration.rb
+++ b/activesupport/lib/active_support/duration.rb
@@ -70,12 +70,10 @@ module ActiveSupport
     alias :until :ago
 
     def inspect #:nodoc:
-      val_for = parts.inject(::Hash.new(0)) { |h,(l,r)| h[l] += r; h }
-      [:years, :months, :days, :minutes, :seconds].
-        select {|unit| val_for[unit].nonzero?}.
-        tap {|units| units << :seconds if units.empty?}.
-        map {|unit| [unit, val_for[unit]]}.
-        map {|unit, val| "#{val} #{val == 1 ? unit.to_s.chop : unit.to_s}"}.
+      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 => :en)
     end