[marcosdumay]

Collision-free hashes exist. They are just not used on practice to build hash maps, but if you use a 128 bits hash with homogeneous distribution, handling collisions is irrelevant.

Besides, just because you are storing the keys, it doesn't mean it is viable to retrieve them. On the collision aware maps you see on CS, iterating through the keys is extremely inefficient.

The OP's description is clearly somebody that has learned the theory, but don't have any practical knowledge.