One of the most amazing features of Clojure is the ability to decorate references to objects with metadata, as in the following example:

user> (def my-user {:login “pcalcado” :password “secret123″})
#’user/my-user
user> my-user
{:login “pcalcado”, :password “secret123″}
user> ^my-user
nil
user> (def my-cached-user (with-meta my-user {:cached-at (java.util.Date. )}))
#’user/my-cached-user
user> my-cached-user
{:login “pcalcado”, :password “secret123″}
user> ^my-cached-user
{:cached-at #}
user> my-user
{:login “pcalcado”, :password “secret123″}
user> ^my-user
nil

That feature makes the […]