Add 'Feature Envy' smell and refactorings

Author: Ben Christel

Diff for: docs/refactorings/move-method.md

@@ -0,0 +1,33 @@
+# Move Method
+
+## Example
+
+### Before
+
+```ruby
+class PaymentCalculator
+  def invoice_total
+    @invoice.parts.map(&:price).reduce(:+) + @invoice.labor
+  end
+
+  # ...
+end
+```
+
+### After
+
+```ruby
+class PaymentCalculator
+  # ...
+end
+
+# ...
+
+class Invoice
+  def total
+    parts.map(&:price).reduce(:+) + labor
+  end
+
+  # ...
+end
+```

Diff for: docs/smells/README.md

@@ -47,7 +47,7 @@ Fowler's book, _Refactoring: Improving the Design of Existing Code_.
 ## Objects and Messages
 
 - [**Null Check**](null-check.md). Fix with [Introduce Null Object](../refactorings/introduce-null-object.md) or [Introduce Continuation [BC]](../refactorings/introduce-continuation.md).
-- [**Feature Envy.**](http://wiki.c2.com/?FeatureEnvySmell) Fix with [Move Method](), possibly preceded by [Extract Method](../refactorings/extract-method.md).
+- [**Feature Envy.**](feature-envy.md) Fix with [Move Method](../refactorings/move-method.md), possibly preceded by [Extract Method](../refactorings/extract-method.md).
 - [**Primitive Obsession.**](http://wiki.c2.com/?PrimitiveObsession) Fix using [Replace Primitive with Object](). See also [Avoid Hashy Syntax In Ruby](http://wiki.c2.com/?AvoidHashySyntaxInRuby) for a language-specific refactoring technique.
 - [**Multiple Responsibilities.**](http://wiki.c2.com/?OneResponsibilityRule) See also [God Class](http://wiki.c2.com/?GodClass). TODO: how to fix?
 - [**Switch on Type.**](http://wiki.c2.com/?SwitchStatementsSmell) Fix using [Replace Conditional with Polymorphism]().

Diff for: docs/smells/feature-envy.md

@@ -0,0 +1,41 @@
+# Feature Envy
+
+A method cares more about another object's data than about
+its own.
+
+## What It Looks Like
+
+```ruby
+def shipment_delivered?
+  shipment.delivery_date.to_s.strip.empty?
+end
+```
+
+```ruby
+def invoice_total
+  invoice.parts.map(&:price).reduce(:+) + invoice.labor
+end
+```
+
+## Why It Hurts
+
+Feature envy may mask [Duplicated Code](duplicated-code.md)
+since similar envious code may be repeated in multiple
+places. It is often associated with [Message
+Chains](message-chain.md), since the envious code asks for
+and manipulates another object's data and thus has to know
+about the types of those data.
+
+## How To Fix It
+
+Use [Move Method](../refactorings/move-method.md) to move
+the envious code to the envied class. You may have to
+[Extract Method](../refactorings/extract-method.md) first to
+isolate the code that should be moved.
+
+## Related Smells
+
+[Primitive Obsession](primitive-obsession.md) is often a
+sign of hidden Feature Envy. If the primitive were replaced
+by a class you could modify, you could move the
+primitive-obsessed methods to it.