gistfile1.txt

<%= debug @user.user_addresses %>
<%= f.fields_for @user.user_addresses do |ua| %>
  <%= debug ua.object.is_home_address %>
  <%= debug ua.object.is_work_address %>

and in the browser I get this 

---
- !ruby/object:UserAddress
  attributes:
    id: 
    user_id: 
    country: 
    state: 
    zip: 
    street: 
    city: 
    is_delivery_address: 
    is_home_address: true
    is_work_address: 
    is_billing_address: 
    other_address_info: 
    street2: 
    fax: 
    phone: 
- !ruby/object:UserAddress
  attributes:
    id: 
    user_id: 
    country: 
    state: 
    zip: 
    street: 
    city: 
    is_delivery_address: 
    is_home_address: 
    is_work_address: true
    is_billing_address: 
    other_address_info: 
    street2: 
    fax: 
    phone: 
--- 
...