I'm trying to use the REST API generator for a series of calls like this, 

import vibe.d;

interface MyInterface {
  @property string emit_json();
}

class MyClass : MyInterface {
  @property string emit_json() {
    Json j = Json.emptyObject;
    j.foo = "123";
    j.bar = "456";
    j.quxx = "789";
    return j;
  }
}

shared static this() {
    ...
        auto router = new URLRouter;
        router.registerRestInterface(new MyClass);
    ...
}

but this fails to compile on implicit conversion: 

source/app.d(14): Error: cannot implicitly convert expression (j) of type Json to string

I tried generating a string, 

    string s = j.toString();
    return s;

but the return goes through another string conversion and gets escaped: 

$ curl -v http://127.0.0.1:8080/emit_json
* Hostname was NOT found in DNS cache
*   Trying 127.0.0.1...
* Connected to 127.0.0.1 (127.0.0.1) port 8080 (#0)
> GET /emit_json HTTP/1.1
> User-Agent: curl/7.37.1
> Host: 127.0.0.1:8080
> Accept: */*
>
< HTTP/1.1 200 OK
* Server vibe.d/0.7.20 is not blacklisted
< Server: vibe.d/0.7.20
< Date: Sun, 31 Aug 2014 20:53:22 GMT
< Keep-Alive: timeout=10
< Content-Type: application/json; charset=UTF-8
< Transfer-Encoding: chunked
<
* Connection #0 to host 127.0.0.1 left intact
"{\"foo\":\"123\",\"bar\":\"456\",\"quxx\":\"789\"}"

What is the proper way to produce and return JSON via the REST API generator? Am I missing the intention/abusing the generator and should just create a HTTP route for each and set the response type?

Thanks.