how to define static variable across a partial?

I'm not sure if this is what you're asking but this is what i've
implemented in a partial called _newest_date.rhtml :

  <% if newest_date.created_at == newest_date.updated_at %>
    <%= newest_date.created_at.strftime("Created on %m/%d/%Y") %>
    <%= newest_date.created_at.strftime("at %I:%M%p") %>
  <% else %>
    <%= newest_date.updated_at.strftime("Updated on %m/%d/%Y") %>
    <%= newest_date.updated_at.strftime("at %I:%M%p") %>
  <% end %>

And i call this for every post that is shown in a page. With a little
more detail the list.rhtml file :

<% for post in @posts %>
  <div class="post" id="post_<%= %>">
    <h3><%= link_to h(post.title), :action => 'edit', :id => post %></

    <ul class="post_info">
      <%= render :partial => 'newest_date', :object => post %>

    [.... stuff here.....]

<% end %>

You could call a partial like this one from inside another partial.

I'm pretty sure this is NOT the best way to do it, but i'm pretty new
at rails so this is a *fast* solution i found for my problem, which in
this case is to either print the created_at date or the updated_at
date according to which one is the newest.

P.S.: The controller just returns the @posts collection through a
paginator :

  def list
    @post_pages, @posts = paginate :posts, :order => 'id
DESC', :per_page => 10

--Hope i helped a little