Complexity nomenclature

[Nordlöw via Digitalmars-d]

On Saturday, 5 December 2015 at 20:48:16 UTC, Andrei Alexandrescu 
wrote:
> Then what do we do with more complex relationships like O((m + 
> n) log n) etc.

What about a compile-time expression tree similar to how, for 
instance, `BaseUnit`, `ScaledUnit`, (and suggestedly 
`ShiftedUnit` and `LinearUnit`), are defined and used in David 
Nadlinger's std.units?