Null Object Pattern

Presented to @paperlessdev on 9/28/12

Transcript

1. Null Object Pattern Friday, September 28, 12
2. Last week I went here: Friday, September 28, 12
3. And I learned about this thing called the Null Object Pattern. Friday, September 28, 12
4. Right now we do things like this: if @guest && @guest.attending? do_attending_stuff end Friday, September 28, 12
5. The Null Object Pattern seeks to remove the excess logic. @guest = Guest.find_by_id(params[:id]) || NullGuest.new ... class NullGuest def attending? false end end Friday, September 28, 12
6. But this can get a bit tedious: class NullGuest def act!(action) end def additional_guests nil end def attending? false end def blank_name? true end def display_name_or_email nil end def email_address nil end def email_address_id nil end def member? false end def not_attending? false end ... Friday, September 28, 12
7. So I wrote a gem to make it easier: GordonDiggs/nobody Friday, September 28, 12
8. How it’s used class NulllGuest include Nobody returns_false_for :attending?, :not_attending? returns_true_for :blank_name? returns_nil_for :display_name, :personal_note def state 'initialized' end end Friday, September 28, 12
9. How it works • Define methods on the given class that return a specific value using Ruby’s define_method • Could in theory allow any return value Friday, September 28, 12
10. Final thoughts • The wiki page on Null Object Pattern sucks. Don’t read it. • Null classes can get tricky because of coupling • Metaprogramming is hard. Friday, September 28, 12
11. Thank you github.com/GordonDiggs/nobody gem install nobody Friday, September 28, 12