title: Devise + CanCan just prevent other users from editing objects
body: <p>How would you prevent other users from editing a object, say a profile object that does - not - belong to themselves?</p>
  
  <p>Most online examples are complexes with multiple user roles, i haven't been able to get this working, must be simple though:</p>
  
  <pre><code>  def initialize(user)
  
        can :update, Profile do |profile|
          profile.try(:user) == current_user
        end
  
    end
  </code></pre>
  
  <p>And inside my ProfilesController#edit</p>
  
  <pre><code>authorize! :update, @profile
  </code></pre>