Const sucks

[Walter Bright]

Gregor Richards wrote:
> const has a more limited use for optimization than invariant, since the 
> value could be changed by other threads/programs-with-shm/whatever from 
> under you.

const is useless for optimization, invariant is very useful for 
optimization. But it turns out that if you have invariant, soon you'll 
discover that you need const. Otherwise you'll find that every function 
will have to be implemented two or more times (*).

(*) Because invariants cannot be implicitly converted to mutable, and 
vice versa.