This class implements an LRU dictionary cache. The two operations on it are 
get() and set(), both of which promote the key being referenced to the ``top'' 
of the cache, so it will stay alive longest. When the cache is full and a 
new item needs to be added, the oldest one is thrown away. You should be able 
to regenerate the data at any time, if get() returns undef. This class is 
useful for caching information from a slower data source while also keeping 
a bound on memory usage. 

WWW: http://livejournal.com/code/cache/