why not just use a random number generator as a hash function?
If I understand the question correctly, the answer is simple: if Hash(object) returns 27 when you call it this afternoon, we want Hash(object) to return 27 if we call it next week, on a different computer. If you use a random number generator in such a way that this is guaranteed, then go for it. Consider that a key use case for hash functions is implementing hash tables, and we want to be able to access what we put into a hash table tomorrow with the key we used today.

In your example, you might want to add a contains(value) method; using the hash, this would be as easy as checking self.hash[value] =? value. Otherwise, you'd need to iterate through the entire array to see if some position contains value.