<% @somethings.each do |something| %>
  <%= cache("somethings:#{something.id}", :time => something.created_at) do %>
    <div class="something">
      <%= render "somethings/expensive_calculation" %>

      <!-- time.strftime(...) calculated dynamically every time -->
      <p class="timestamp"><%= time.strftime("%B %d, %Y") %></p>
    </div>
  <% end %>
<% end %>