For various reasons, it would be really nice to be able to generate a series of unique ordinal values (say integers, but really anything that is easily less_than_comparable) at compile time. A concrete example : struct system1 : ordinal<0> { }; struct system2 : ordinal<1> { }; etc... Now, if these tags can be defined in user code in various places, it can be difficult to ensure that there is no duplication of the ordinal values. What I want is something like this: struct system1 : ordinal<get_next_system_ordinal()> { }; struct system2 : ordinal<get_next_system_ordinal()> { }; where I don't really care what the specific order is, just that the ordinal values are unique... Anyone have a bright idea on how to accomplish this? Preprocessor? Matthias