Using a Set for UDTs, how is uniqueness established?

[Ali Akhtar]

I have a UDT which contains a text 'id' field, which should be used to
establish the uniqueness of the UDT.

I'd like to have a set<my_udt> field in a table, and I'd like to use the id
of the udts to establish uniqueness.

Any ideas how this can be done? Also using Java, and c* 3.7