const by default.

[Deewiant]

BCS wrote:
> However if you are passing them to a function they become implicitly
> immutable unless you say otherwise. (Assume that "@" is the grant
> mutability operator)
> 
> void fn4()
> {
>     char[] c;
> 
>     c[5] = '\0';    // allowed
> 
>     fn1(c);        // allowed
>     fn2(c);        // not allowed: arg 1 is mutable;
>     fn2(@c)        // allowed
> }
> 
> In the general case I expect that this change will have little effect on
> code. In my experience, most pass by reference cases are immutable
> anyway. The rest should be easy to find and fix as long as DMD gives
> good error messages.

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.

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.