[Rcpp-devel] reference classes in C++ :is it possible?

[Steven Varga]

Hi Dirk,

yes it would,

1) my_class::my_method delegates to ReferenceClass::my_method  [c++ method
exported]
2) ReferenceClass(R)::my_method callSuper() --> [ infinite recursion!!! ]
3) smoke + possible explosion + ... random events from HR department

or some benefits:
1) my_class::my_method delegates to ReferenceClass::my_method
2) ReferenceClass(R)::my_method ( works hard to solve some problem )
3) abstract class with R reference class impl

This is still based on the assumption that one can call a ReferenceClass
method... if so this may open up a door to design interfaces in c++ and
implementing them in R. With some limitations: my_class::my_method()=0;
would need some stub generated and linked to call R reference class. (if
that possible at all)

I don't not have the necessary experience to oversee all the implications
of a feature/bug outlined; but find it an appealing thought to able to
extend a c++ class in R where c++ runtime has the ability to call the R
implementation.

[c++ Interface_a]  ---> [c++ Abstract_ab  ] ---> Rcpp_export  -> | R
c_runtime | -> [ RrefClass  impl_ab]
[c++ Interface_b]  --|

[ some infrastructure to process/direct data flow ]
-------------------------------->      [ set of implementations to choose
from ]

steve

On Fri, Mar 1, 2013 at 6:35 PM, Dirk Eddelbuettel <edd at debian.org> wrote:

>
> Hi Steven,
>
> On 1 March 2013 at 14:34, Steven Varga wrote:
> |
> | Hello
> |
> | First thanks Dirk for the quick reply and the hint; Mr.  John Chamber's
> | implementation is great! gone through the documentation and followed his
> | instructions. Worked well.  Only one way though -- as you pointed out.
> |
> | I was able to get the fields from the extended class; if someone could
> point
> | into the direction how to get/execute methods of a Reference Class  then
> it may
> | be doable??
>
> Just making sure I understand: So you want to access part of a reference
> class from C++? Wouldn't that violate the 'one way only view?
>
> Dirk
>
> |
> |  ..... c++ class ......
> |     void set_reference( SEXP xptr_){
> |         Rcpp::Reference ref(xptr_);
> |         ref.field("some_field"));   // get the field data
> |
> | // -------  this is not implemented, any hints?  --------
> |         ref.method("some_method")( x, y);  // this would be nice to have
> |     }
> | ...... end .......
> |
> | setRcppClass("World",
> |     module="yada",
> |     fields = list( some_field = "character"),
> |     methods = list(
> |           initialize = function(){
> |                 some_field <<- "field value set"
> |                 callSuper()                # call constructor
> |                 set_reference( .self ) # pass 'this'
> |           }
> |      ),saveAs="genWorld"
> | )
> |
> | On Thu, Feb 28, 2013 at 8:15 AM, Dirk Eddelbuettel <edd at debian.org>
> wrote:
> |
> |     On 28 February 2013 at 04:44, Steven Varga wrote:
> |     | I am trying to create an abstract pattern using R reference
> objects in
> |     C++;
> |     | anyone knows if this is possible/not possible? Where to look?
> |
> |     I am not sure you can. The best (only ?) relevant documentation
> might be
> |     John
> |     Chamber's example of 'Rcpp Classes' (see help(setRcppClass) in R
> once Rcpp
> |     is
> |     loaded).
> |
> |     And as I recall, he is pretty explicit that you can take a C++ class
> and
> |     "extend" it for prototyping from the R side, but that you cannot
> access
> |     those
> |     extended parts from C++ as only R sees it.  I think you are hitting a
> |     similar
> |     constraint here.
> |
> |     It would be nice if this worked but I am not quite sure that it can.
> |
> |     Dirk
> |
> |     --
> |     Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
> |
> |
> |
> |
> | ----------------------------------------------------------------------
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> | Rcpp-devel at lists.r-forge.r-project.org
> | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
> --
> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
>
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