+ redef fun hash
+ do
+ if hash_cache == null then
+ # djb2 hash algorithm
+ var h = 5381
+ var i = length - 1
+
+ for char in self.chars do
+ h = (h * 32) + h + char.ascii
+ i -= 1
+ end
+
+ hash_cache = h
+ end
+ return hash_cache.as(not null)
+ end
+