order relation on lumiera::P incompletely defined

[ichthyo]

Just discovered by accident, that lumiera::P suffers from the same logical omission, which has biten me badly in the last days with respect of using ordered types within associative containers: The relation needs to be complete (either partial or total), and the null-check guard defeats that.

We need to find a consistent way how to interpret NIL pointers, and then we need to enforce this policy.

• either NIL pointers are disallowed when it comes to comparisons (i.e. the opeators throw or assert)
• or we interpret NIL pointers as bottom -- but then each and every container needs to be able to deal with bottom

[ichthyo]

Intuitively I'd prefer the first solution. I'd rather introduce an empty representation object than start introducing special cases at the level of element / container handling. But the downside is that disallowing comparisons on NIL pointers (recall, P is a smart-ptr, so NIL is not NULL) may be quite hash for the occasional user.

Anyway, I'll take the experimental approach here and just add the relevant assertions ... and then wait for problems bubbling up

[ichthyo]

no serious problems meanwhile with that approach, but indeed not much possibilities for problems arising here currently, as most of the operations on objects within the session are still unimplemented. Anyhow, closing that for now, the chosen solution (disallow NIL on comparisions) seems the most logical one....