Rails Refactoring Example: Introduce Null Object

A questionable use of Null Object pattern; a typical Advanced Beginner approach.

April 11, 2012 Tagged: patterns refactoring null object Comments (View) Rails Refactoring Example: Introduce Null Object You probably don’t write code like this: if object.kind_of?(User) do_this else object.do_that end Why not? Because Ruby encourages duck typing and polymorphism. A hidden version Here’s the same principle: if object.nil? do_this else object.do_that else This checks that object is of type NilClass instead of type User . The pattern There’s an old pattern called Null Object that addresses this special case of avoiding type-checking in favor of duck typing. Here’s an example of the “Introduce Null Object” refactoring to fix this problem with a Null Object in a Rails app. The code to be refactored Airbrake reports an error from this line in a Haml view: = l location.orders.ascend_by_created_at.first.created_at.to_date Demeter is displeased but let’s fix the p...

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