const by default.

[BCS]

Deewiant wrote:
> 
> 
> I think there's a problem with all this "grant mutability/immutability", which
> is that we're just degenerating into C++ with its const_cast. With it, the
> compiler has few, if any, guarantees about the constness of anything --- it can
> always be casted away.

Casting away mutability (unless I'm totally nuts) is always safe. 
Casting away immutability should never be allowed.

> 
> The way I see it, something either is or isn't mutable, and it should stay that
> way for the duration of the program --- in some cases, for the duration of a
> function or the lifetime of an object.

Each specific reference *would* be mutable or immutable for it's entire 
duration. It would be a compile time attribute of a reference. The only 
time that the mutability of a reference would change is when it is 
copied to another reference, in a function call for instance, and then 
the only change that can be made is the new reference can *lose* mutability.