opDispatch and operator overloads

[John Colvin]

struct S {
        auto opDispatch(string s)(A i){}
}
struct A {}

void main() {
        S s;
        A a;
        s + a; //Error: incompatible types for ((s) + (a)): 'S' and 'A'
}

It would be really nice if opDispatch could catch missing 
operator overloads.

Also, would it be a good idea to have free functions of all the 
operators (opOpAssign etc...) for builtin types somewhere? It's 
occasionally useful in generic wrappers.