Hello Matthias, Thursday, March 1, 2007, 12:08:50 AM, you wrote:
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?
Just a thought... Maybe something like this might help: typedef [implementation defined] uint_ptr_t; template< typename > void foo() {} template< typename T, uint_ptr_t TagV = (uint_ptr_t)&foo< T > > struct ordinal : public mpl::integral_c< uint_ptr_t, TagV > { }; struct system1 : ordinal< system1 > {}; struct system2 : ordinal< system2 > {}; The uint_ptr_t type should be large enough to accomodate a pointer to function. It is needed since function pointers cannot be ordered. I suspect, not all compilers would allow this. -- Best regards, Andrey mailto:andysem@mail.ru