guava scalaz memo

Caching.scala

def guavaMemo[K, V](ttl: CacheTtl): Memo[K, V]
    = Memo.memo[K, V] { method: (K => V) =>
    val builder: CacheBuilder[AnyRef, AnyRef] = CacheBuilder.newBuilder()
    builder.expireAfterWrite(ttl.time, ttl.unit)
    val cache = builder.build().asInstanceOf[Cache[K, V]]
    def ret(key: K): V = cache.get(key, new Callable[V] {
      override def call(): V = {
        method(key)
      }
    })
    ret
}