with not working wtih BitFlags

[Jot via Digitalmars-d-learn]

struct EnumToFlags(alias E) {
        template opDispatch(string Name) {
                enum opDispatch = 1 << __traits(getMember, E, Name);
        };
};


enum X
{
a,b,c
}

auto q = EnumtoFlags!X;


auto m = q.a;

with(q)
{
   auto m = a;
}

a undefined.

Any way to get it to work? Maybe a full blowing string mixin is 
needed to generate the flag enum?