[Rcpp-devel] module/S4 retval

[Richard Downe]

In the interest of sharing, I figured I should supply what eventually 
worked.

I'm kicking myself, because I tried this early on when I was trying to 
create an SEXP operator, and abandoned it because of const conflicts, 
but by using a pure object factory that sidestepped the need for the 
SEXP operator, I was able to use this without issue:

         Rcpp::Reference 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()) {
                 return Rcpp::internal::make_new_object( new 
morphologyIndices( fusKey ) );
             }
             else {
                 stringstream errorMessage;
                 errorMessage << "No fusion with fusid = " << fusKey << 
" or specified fusion not associated "
                              << "with current registration object.";
                 throw runtime_error( errorMessage.str() );
             }
         }

A single call to make_new_object, defined in Module.h, taking as an 
argument a pointer to the target class fully initializes all the 
Rcpp::Module infrastructure, and everything is happy.
-rd

On 09/06/2012 09:53 AM, Dirk Eddelbuettel wrote:
> On 6 September 2012 at 09:42, Richard Downe wrote:
> | 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
>
> Actually as Reference Classes -- see help(setRefClass) about them.  John as
> added to this to extend Rcpp modules with the ability to extend what we get
> from the C++ classes via Rcpp modules on the R side. He called it Rcpp
> classes, and there is a little bit in the current Rcpp versions.
>
> | 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.
>
> "There should be" but I can't guide you on this. On the Rcpp side this is
> code written by Romain who is currently taking a less active role. He may
> read this message, or may not.  So you are on your own.
>
> But starting there, methinks, gives you a better starting point than starting
> at the raw C API for R.
>
> Dirk
>
> | -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
> | > | >
> | > |
> | >
> |
>