[Rcpp-devel] module/S4 retval

[Richard Downe]

Absolutely, my apologies, I'd just been hitting "reply".

It does appear as though instances of "classes" as encapsulated by 
modules show up in R as S4 objects.  I had naively thought that by using 
the Rcpp::S4 constructor I could return a valid instance, but there is 
clearly quite a bit of magic going on (I still can't quite figure out 
how to shoehorn my XPtr into the S4 object properly).

I've been debating trying to figure out how to construct one using the 
raw R C api, but if there's a way to piggyback on the modules code in a 
way that lets me instantiate an instance of my R module class from the 
c++ side (but presumably present said value to wrap() as an S4 object) 
that would be ideal.
-rd

On 09/06/2012 06:25 AM, Dirk Eddelbuettel wrote:
> Good post -- should we keep this on rcpp-devel ?
>
> Not many people in the C++ and R and S4 and Rcpp intersection, I don't hit
> all of these as I do little S4 :)
>
> Dirk
>
> On 5 September 2012 at 23:17, Richard Downe wrote:
> | Yeah...after some consultation with other c++ hacks, it sounds as though
> | using regexps with perl or python to generate the module declaration is
> | far cleaner than anything I could do with template metaprogramming.
> |
> | I did find a boost library called "mirror" which, if it ever makes it
> | into mainline boost, might be safe to use in Rcpp, at least optionally,
> | to automagically export all public members, but as long as it's outside
> | the official distribution, simply parsing the headers in the "configure"
> | script and including the result with #include is far less work  (I think
> | I'm going to use comment block markers, such as
> | // @@BEGIN_RCPP_EXPORTS@@
> | to bound the parts of the header I want slurped into a module delcaration).
> |
> | I do seem to have 1 residual sticking point.  When, in my object
> | factory, I call the Rcpp::S4 constructor on a class name, that works,
> | but then I can't seem to find a valid means of binding the pointer.
> |
> | Attached is what I'm attempting -- I'm assuming there's a better way
> | (perhaps by somehow accessing the module's bound ctor?)?
> |
> |          Rcpp::S4 CreateBLMorph(long fusKey) {
> |              using namespace std;
> |              vector< pair<string,long> > terms;
> |              terms.push_back( make_pair( "fusid", fusKey ) );
> |              terms.push_back( make_pair( "ivussegid",
> | m_regObj.getBLSegID() ) );
> |
> |              pqxx::result res = ExecuteSelect( string("fusion"), terms );
> |
> |              if (res.size()) {
> |                  Rcpp::S4 retVal("Rcpp_morphologyIndices");
> |                  retVal.slot( "pointer" ) = Rcpp::XPtr<
> | morphologyIndices >( new morphologyIndices(fusKey), true );
> |                  return retVal;
> |              }
> |              else {
> |                  stringstream errorMessage;
> |                  errorMessage << "No fusion with fusid = " << fusKey <<
> | " or specified fusion not associated "
> |                               << "with current registration object.";
> |                  throw runtime_error( errorMessage.str() );
> |              }
> |          }
> |
> | -rd
> |
> | On 09/05/2012 08:55 PM, Dirk Eddelbuettel wrote:
> | > Hi Richard,
> | >
> | > On 5 September 2012 at 16:22, Richard Downe wrote:
> | > | I would like to be able to create object factories in my rcpp module,
> | > | such that I can call
> | > | classA::GetInitializedB(), and get an S4 object (module instance?) back.
> | > |  From what I can tell, the "module" class definition macros are not
> | > | quite flexible to permit this, but I'm wondering if there's a way to
> | > | leverage the code in Module.h/cpp in an operator SEXP() block to
> | > | appropriately wrap up object factory pointers.
> | > |
> | > | I really am loathe to have to enumerate all exported methods *again*,
> | > | and would like to be able to use template metaprogramming to slurp in a
> | > | header, parse it, and use that to enumerate the list of methods in the
> | > | returned S4 object.
> | > |
> | > | Has anyone ever done anything like this?
> | >
> | > Not that I can recall. Would be nice to have though.
> | >
> | > I did some work recently with Rcpp modules. It is pretty straightforward, and
> | > if you wanted to, you could probably write a header parser / module
> | > declaration generator. So far, I've been happy to do it by hand as it has not
> | > been reptitive but rather exploratory.
> | >
> | > Dirk
> | >
> |
>