Ability 2 - cancan abstract resource authorization

ability.rb

class Ability
  include CanCan::Ability

  def initialize(user)
    user ||= User.new

    resourceful_actions = [
      :index,
      :show,
      :new,
      :create,
      :edit,
      :update,
      :destroy
    ]

    can :index, [Array, ActiveRecord::Relation] do |list|
      list.first.is_a?(User) && (list.map(&:id) - user.associates.map(&:id)).empty?
    end

    cannot resourceful_actions, User
    can :update, User, :id => user.id
  end

end