From 9d1f6edbe0aa6f95f55464136e39fb4e2e4643f2 Mon Sep 17 00:00:00 2001
From: Carlos Antonio da Silva <carlosantoniodasilva@gmail.com>
Date: Fri, 27 Apr 2012 20:44:08 -0300
Subject: Return earlier if attribute already changed in *_will_change! methods

Avoid obtaining the value and duplicating it when possible.
---
 activemodel/lib/active_model/dirty.rb | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index d327913824..7f7fb90d87 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -151,13 +151,15 @@ module ActiveModel
 
       # Handle <tt>*_will_change!</tt> for +method_missing+.
       def attribute_will_change!(attr)
+        return if attribute_changed?(attr)
+
         begin
           value = __send__(attr)
           value = value.duplicable? ? value.clone : value
         rescue TypeError, NoMethodError
         end
 
-        changed_attributes[attr] = value unless changed_attributes.include?(attr)
+        changed_attributes[attr] = value
       end
 
       # Handle <tt>reset_*!</tt> for +method_missing+.
-- 
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