Add 'Primitive Obsession' smell and refactoring

Author: Ben Christel

docs/refactorings/replace-primitive-with-object.md

@@ -0,0 +1,23 @@
+# Replace Primitive With Object
+
+## Example
+
+### Before
+
+```ruby
+def protocol(url_string)
+  url_string.match(/^([^:]+):/)[1]
+end
+```
+
+### After
+
+```ruby
+def protocol(url)
+  url.scheme
+end
+
+# ... elsewhere ...
+
+url = URI.parse(url_string)
+```

docs/smells/README.md

@@ -48,7 +48,7 @@ Fowler's book, _Refactoring: Improving the Design of Existing Code_.
 
 - [**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.**](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.
+- [**Primitive Obsession.**](primitive-obsession.md) Fix using [Replace Primitive with Object](../refactorings/replace-primitive-with-object.md). 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]().
 - [**Middleman.**]() Fix using [Inline Method](https://refactoring.com/catalog/inlineFunction.html).

docs/smells/primitive-obsession.md

@@ -0,0 +1,32 @@
+# Primitive Obsession
+
+Code manipulates strings and hashes directly instead of
+using domain objects.
+
+## What It Looks Like
+
+```ruby
+protocol = url.match(/^([^:]+):/)[1]
+```
+
+```ruby
+username = user["name"]
+```
+
+## Why It Hurts
+
+- Since you can't define new methods on primitive data types
+(at least not without causing a great deal of confusion),
+logic for manipulating them gets scattered around the
+codebase.
+- Your code becomes coupled to the underlying
+structure of the data, making it harder to test and reason
+about.
+- You have to think about error cases more often. For
+  example, when using a string to represent a URL, you have
+  to think about the case where the string is not a
+  well-formed URL every time you do something with it.
+
+## How To Fix It
+
+[Replace Primitive With Object](../refactorings/replace-primitive-with-object.md).