gistfile1.rb

class PermittedParams < Struct.new(:params, :user)
  def topic
    params.require(:topic).permit(*topic_attributes)
  end

  def topic_attributes
    [:name].tap do |attributes|
      attributes << :sticky if user && user.admin?
      attributes << {posts_attributes: {:"0" => post_attributes}}
    end
  end
  
  def post_attributes
    [:content].tap do |attributes|
      attributes << :inline_images if user && user.admin?
    end
  end
end