Tidier pre/post conditions

[bearophile]

BCS:
> Logging? Any pre conditions that require external services ("DNS names should 
> have been checked at this point.", "key must exist in the DB")?
> Those wouldn't work but I'm not sure how much of an issue they are.

Such usages are not common, and the program behaviour can change between release and not release versions, because you can modify a global variable, but I think forbidding them is not that useful. Turning locally attributes and arguments into const looks enough to me.

Bye,
bearophile