Sharing in D

[Walter Bright]

Sean Kelly wrote:
> What about this:
> 
>     shared ClassA a;
> 
>     void main()
>     {
>         ClassB b = a.getB();
>         b.mutate();
>     }
> 
> I'd imagine the checking will catch common mistakes but not issues
> like the above?  Or will the fact that 'b' is being returned from
> a require the declaration of 'b' to be shared because the value
> may be accessed by both ClassA and anything outside ClassA?

Shared cannot be implicitly cast to unshared. Just like const cannot be 
implicitly cast to mutable.