What's missing to make D2 feature complete?

[via Digitalmars-d]

On Wednesday, 24 December 2014 at 08:22:46 UTC, Daniel Murphy 
wrote:
> The same reasoning applies to making all value parameters 
> mutable.

Yes, but my point was that making all value parameters mutable is 
at odds with correctness when you later edit it since you no 
longer know whether it has been modified or not.

E.g.

int myfunc(int n){
     ...lotsofstuff...
     x = mayormaynotchange(n);
    ...lotsofstuff...
    return n>0 ? x : 0;  // modified from "return x"
}