Let's not make invariants const

[bearophile]

H. S. Teoh:

> IMO, if you need to be changing stuff inside invariants, then 
> you're using it wrong. Invariants are intended to verify 
> program logic, not to do things like altering object state. The 
> point is to be able to compile with invariant code turned off, 
> and still have the program work exactly as before.

I agree, modifying the state of the struct/class instance is not 
the job of contracts and invariants. D contract programming is 
already not tidy, so better to not make it even more messy.

In a perfect world invariants and contracts should be pure too!

Bye,
bearophile