[Rcpp-devel] Wrapping a c++ class with singleton using RCPP Module

[Matthew Supernaw - NOAA Federal]

Hi Nikhil,

Here's an updated version that exposes a FooWrapper class in the module to
the previous posted code. Hopefully this helps!

class FooWrapper{
public:
  Foo* foo_m;
  FooWrapper(){}


  FooWrapper(const FooWrapper& other):foo_m(other.foo_m){

  }

  FooWrapper(Foo* foo):foo_m(foo){

  }

  void SayHello(){
    Rcpp::Rcout << "From \"void SayHello()\" -> "<<(this->foo_m)<<" -> ";
    Rcpp::Rcout << "hello from Foo.\n";
  }

};



RCPP_EXPOSED_CLASS(FooWrapper)

  FooWrapper GetSingleton(){
    FooWrapper ret(Foo::GetSingleton());
    Rcpp::Rcout<<"From \"Foo& GetSingleton()\" -> memory address for
singleton is " <<ret.foo_m<<"\n";
    return ret;
  }





RCPP_MODULE(foo) {
  Rcpp::class_<FooWrapper>("Foo")
  .constructor()
  .method("SayHello", &FooWrapper::SayHello);
  Rcpp::function("GetSingleton", &GetSingleton);

}

On Wed, Feb 21, 2024 at 10:51 AM Matthew Supernaw - NOAA Federal <
matthew.supernaw at noaa.gov> wrote:

> Looks like I posted too soon. I just noticed the memory address from the
> "SayHello" function doesn't match.
>
> On Wed, Feb 21, 2024 at 10:47 AM Matthew Supernaw - NOAA Federal <
> matthew.supernaw at noaa.gov> wrote:
>
>> Hi Nikhil,
>> I'm not exactly sure what you are trying to do, but I hope this simple
>> example is helpful.
>> Thanks.
>> Matthew
>>
>>
>> #include <Rcpp.h>
>> using namespace Rcpp;
>>
>>
>> class Foo{
>> public:
>>   static Foo* singleton;
>>
>>   Foo(){
>>   }
>>
>>   void SayHello(){
>>     Rcpp::Rcout << "From \"void SayHello()\" -> "<<this<<" -> ";
>>     Rcpp::Rcout << "hello from Foo.\n";
>>   }
>>
>>   static Foo* GetSingleton(){
>>
>>     if(singleton == NULL){
>>       Foo::singleton = new Foo();
>>     }
>>     Rcpp::Rcout<<"From \"static Foo* GetSingleton()\" -> memory address
>> for singleton is " <<Foo::singleton<<"\n";
>>     return Foo::singleton;
>>   }
>> };
>>
>> Foo* Foo::singleton = NULL;
>>
>> RCPP_EXPOSED_CLASS(Foo)
>>
>>   Foo& GetSingleton(){
>>     Foo* foo_singleton = Foo::GetSingleton();
>>     Rcpp::Rcout<<"From \"Foo& GetSingleton()\" -> memory address for
>> singleton is " <<foo_singleton<<"\n";
>>     return *foo_singleton;
>>   }
>>
>> RCPP_MODULE(foo) {
>>   Rcpp::class_<Foo>("Foo")
>>   .constructor()
>>   .method("SayHello", &Foo::SayHello);
>>   Rcpp::function("GetSingleton", &GetSingleton);
>>
>> }
>> //From R
>> // library(singleton)
>> // library(Rcpp)
>> //
>> // foo <- Rcpp::Module("foo", PACKAGE = "singleton")
>> //
>> // foo_singleton<-foo$GetSingleton()
>> // foo_singleton$SayHello()
>>
>> // Output:
>> // From "static Foo* GetSingleton()" -> memory address for singleton is
>> 0x7fcdf9387590
>> // From "Foo& GetSingleton()" -> memory address for singleton is
>> 0x7fcdf9387590
>> // From "void SayHello()" -> 0x7fcdf9392b60 -> hello from Foo.
>>
>> On Wed, Feb 21, 2024 at 1:34 AM Nikhil Garg <nikhilgarg.gju at gmail.com>
>> wrote:
>>
>>> Hi,
>>>
>>> I am looking for some advice or hoping someone can point me in the right
>>> direction for wrapping a C++ class with singleton using Rcpp. I have been
>>> using RCPP modules for some of this work but got stuck with a C++ object
>>> which returns a singleton.
>>>
>>> Here is the general structure of the object
>>>
>>> class Foo {
>>>     public:
>>>         Foo();
>>>         ~Foo();
>>>
>>>         static Foo &getFoo();
>>>         Foo(Foo const&) = delete;
>>>         void operator=(Foo const&) = delete;
>>> }
>>>
>>> Regards,
>>> Nikhil
>>> _______________________________________________
>>> Rcpp-devel mailing list
>>> Rcpp-devel at lists.r-forge.r-project.org
>>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>>>
>>
>>
>> --
>> Matthew Supernaw
>> *Scientific Software Developer*
>> *National Oceanic and Atmospheric Administration*
>> *Office Of Science and Technology*
>> *NOAA Fisheries | *U.S. Department of Commerce
>> Phone 248 - 396 - 7797
>>
>>
>>
>
> --
> Matthew Supernaw
> *Scientific Software Developer*
> *National Oceanic and Atmospheric Administration*
> *Office Of Science and Technology*
> *NOAA Fisheries | *U.S. Department of Commerce
> Phone 248 - 396 - 7797
>
>
>

-- 
Matthew Supernaw
*Scientific Software Developer*
*National Oceanic and Atmospheric Administration*
*Office Of Science and Technology*
*NOAA Fisheries | *U.S. Department of Commerce
Phone 248 - 396 - 7797
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