jasonrudolph · October 23, 2011 13:56 · Oct 23, 2011
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+# "SOLID Object-Oriented Design" by Sandi Metz @ GoRuCo 2009
+
+Date: May 30, 2009
+
+[Video on confreaks.net](http://confreaks.net/videos/240-goruco2009-solid-object-oriented-design)
+
+## Notes
+
+* Design is *all* about dependencies
+    * If you *refer* to something, you depend on it.
+    * When the things you depend on change, you must change.
+* Resistance is a resource => Listen to what the pain is telling you.  Listen to what the code smells are telling you.  Embrace the friction.  Fix the problem.
+* On assessing the design:
+    * When you get to the refactor stage of red-green-refactor, ask yourself ...
+        * Is it DRY?
+        * Does it have one responsibility?
+        * Does everything change at the same rate?
+        * Does it depend on things that change less than it does?
+    * When the answer to *all* of these things is 'yes', the design is probably in good shape.
+* "Triangle of Responsibility" Refactoring
+    1. Refactor
+    2. Extract - Pull functionality out where necessary
+    3. Inject - Inject that new dependency into place from which it was extracted
+* What if I don't know where I want this refactoring to take me?
+    * That's OK.  In fact, that's typical.
+    * "Refactor, not because you *know* the abstraction, but because you want to *find* it."
+    * "You don't have to know where you're going to successfully refactor."
+    * When you see someone's code and think it's beautiful and you wonder how they thought of it, they didn't.  They evolved it to that point.
+* When injecting dependencies into a class, do so only via arguments to the #initialize method    
+
+        def intialize(downloader=FTPDownloader.new)
+          @downloader = downloader
+        end
+
+* When you need to inject a few dependencies, you can use an options hash to remove the dependency on the order of the arguments
+
+        def intialize(opts)
+          @env     = opts[:env] || Rails.env
+          filename = opts[:filename]
+        end
+
+* How to assess: "Does each object depend on things that change less than it does?"
+    * Line up the objects from left to right
+        * Left = lower likelihood of change
+        * Right = higher likelihood of change
+    * Only depend on things on your left
+* Recommended reading
+    * [Design Principles and Design Patterns](http://www.objectmentor.com/resources/articles/Principles_and_Patterns.pdf) paper by Robert Martin
+    * [Growing Object-Oriented Software Guided by Tests](http://www.growing-object-oriented-software.com/) by Steve Freeman and Nat Pryce
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