`Rcpp::wrap` and `Rcpp::as` for external classes that use Rcpp namespace classes

Question

How can Rcpp::wrap and Rcpp::as methods be written for classes that contain an Rcpp class?

For example, the following .cpp file compiles using sourceCpp():

#include <Rcpp.h>

namespace Rcpp {
  class myVector {
  public:
    NumericVector data;
    myVector(NumericVector v) : data(v) {};
  };

  template <> myVector as(SEXP v) { 
    return myVector(v);
  }

  template <> SEXP wrap(const myVector& v) { 
    return v.data;
  }
}

//[[Rcpp::export]]
Rcpp::myVector test(Rcpp::myVector& x){
  return x;
}

In this example, we create a vector that is comprised simply of a single Rcpp class (NumericVector) and an Rcpp::as and Rcpp::wrap method so that it can be used as an argument in any exported function.

However, the code does not pass when creating an Rcpp package as follows:

1. Rstudio -> New Project -> New Directory -> R package using Rcpp
2. Copy above script into new file, test.cpp
3. Build -> Install and Restart

There are no complaints about the test.cpp but there are complaints in src/RcppExports.cpp. Here's the relevant function:

// test
Rcpp::myVector test(Rcpp::myVector& x);
RcppExport SEXP _test_test(SEXP xSEXP) {
BEGIN_RCPP
    Rcpp::RObject rcpp_result_gen;
    Rcpp::RNGScope rcpp_rngScope_gen;
    Rcpp::traits::input_parameter< Rcpp::myVector& >::type x(xSEXP);
    rcpp_result_gen = Rcpp::wrap(test(x));
    return rcpp_result_gen;
END_RCPP
}

The errors are:

Line 19: `myVector` does not name a type;
Line 24: `myVector` was not declared in this scope
... template argument 1 invalid, qualified-id in declaration, 'x' not declared, 'test' not declared... side-effects of above two errors.

I do know how to write Rcpp::as and Rcpp::wrap for classes that do NOT contain Rcpp classes (templated case, general case):

1. #include <RcppCommon.h>
2. Forward-declaration of class, may depend on C++ libraries (not Rcpp.h)
3. #include <Rcpp.h>

Unfortunately, Rcpp::myVec requires Rcpp.h and thus cannot be declared prior to including Rcpp.h.

Can external classes containing Rcpp classes make use of Rcpp::wrap and Rcpp::as? If so, is there any precedent I can view for details? I haven't found any despite quite a bit of searching, or maybe I'm overlooking something very simple.