LRUHash

This is a hash class that closely mimicks the original Ruby hash with a subtle difference. It is limited in size and cannot grow beyond a max value. This is done by maintaining the hashed objects in activity order (both insertion and access activities) and removing the least recently used item if the hash exceeds its size limit. 

Pros 

Useful for implementing in-process caches where memory growth control is desired

Cons

Currently you can only control the number of entries in the Hash as opposed to the memory it uses. Providing an estimation of object memory consumption will make the insertion process a lot slower (except if we limit the values to something like strings). That's why I decided I can live with this limitation though.

Example

myhash = LRUHash.new
myhash.max = 2

myhash[1] = 1
myhash[2] = 2

myhash.length # => 2

myhash[3] = 3

myhash.length # => 2

myhash[1] # => nil