r-使用Rcpp模块公开带有引用参数的c++类方法时出错

r - Error exposing c++ class method with reference parameter using Rcpp modules

本文关键字：参数 c++ 类方法 出错 引用 Rcpp 使用 模块      更新时间：2023-10-16

我的目标是构建一个数据集类和一个模型类，并将它们都公开给R。模型类有一个引用数据集实例的train()方法，这似乎是我问题的根源。这是的样子

//glue.cpp
#include <Rcpp.h>
class MyData
{
public:
MyData() = default;
};
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... "; };
};
// Expose MyData
RCPP_MODULE(MyData){
Rcpp::class_<MyData>("MyData")
.constructor()
;
}
// Expose MyModel
RCPP_MODULE(MyModel){
Rcpp::class_<MyModel>("MyModel")
.constructor()
.method("train", &MyModel::train)
;
}

(我应该注意，这个文件glue.cpp嵌入在一个R包中。)当我删除这一行.method("train", &MyModel::train)时，我可以通过pkgbuild::compile_dll()编译它而不会出错。有了它，我得到下面的严重错误

─  installing *source* package ‘SimpleCppModel’ ...
** libs
clang++  -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG  -I"/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include" -I/usr/local/include  -std=c++14 -fPIC  -Wall -g -O2  -c RcppExports.cpp -o RcppExports.o
clang++  -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG  -I"/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include" -I/usr/local/include  -std=c++14 -fPIC  -Wall -g -O2  -c glue.cpp -o glue.o
In file included from glue.cpp:3:
In file included from /Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp.h:27:
In file included from /Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/RcppCommon.h:168:
In file included from /Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/as.h:25:
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/internal/Exporter.h:31:28: error: no matching constructor for initialization of 'MyData'
Exporter( SEXP x ) : t(x){}
^ ~
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/as.h:87:41: note: in instantiation of member function 'Rcpp::traits::Exporter<MyData>::Exporter' requested here
::Rcpp::traits::Exporter<T> exporter(x);
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/as.h:152:26: note: in instantiation of function template specialization 'Rcpp::internal::as<MyData>' requested here
return internal::as<T>(x, typename traits::r_type_traits<T>::r_category());
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/InputParameter.h:72:54: note: in instantiation of function template specialization 'Rcpp::as<MyData>' requested here
ConstReferenceInputParameter(SEXP x_) : obj( as<T>(x_) ){}
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:129:58: note: in instantiation of member function 'Rcpp::ConstReferenceInputParameter<MyData>::ConstReferenceInputParameter' requested here
typename Rcpp::traits::input_parameter<U0>::type x0(args[0]);
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:127:5: note: in instantiation of member function 'Rcpp::CppMethod1<MyModel, void, const MyData &>::operator()' requested here
CppMethod1( Method m) : method_class(), met(m) {} 
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/module/Module_generated_method.h:59:27: note: in instantiation of member function 'Rcpp::CppMethod1<MyModel, void, const MyData &>::CppMethod1' requested here
AddMethod( name_, new CppMethod1<Class,RESULT_TYPE,U0>(fun), valid, docstring);
^
glue.cpp:30:4: note: in instantiation of function template specialization 'Rcpp::class_<MyModel>::method<void, const MyData &>' requested here
.method("train", &MyModel::train)
^
glue.cpp:5:7: note: candidate constructor (the implicit copy constructor) not viable: cannot convert argument of incomplete type 'SEXP' (aka 'SEXPREC *') to 'const MyData' for 1st argument
class MyData
^
glue.cpp:5:7: note: candidate constructor (the implicit move constructor) not viable: cannot convert argument of incomplete type 'SEXP' (aka 'SEXPREC *') to 'MyData' for 1st argument
glue.cpp:8:3: note: candidate constructor not viable: requires 0 arguments, but 1 was provided
MyData() = default;
^
1 error generated.
make: *** [glue.o] Error 1
ERROR: compilation failed for package ‘SimpleCppModel’
─  removing ‘/private/var/folders/dn/9lp6j6j14t1137ftnnk27wyw0000gn/T/RtmpBqDLoF/devtools_install_4d775ed17ea2/SimpleCppModel’
Error in processx::run(bin, args = real_cmdargs, stdout_line_callback = real_callback(stdout),  : 
System command error

什么东西？

正如Dirk在评论中提到的，MyData需要as<>和wrap专业化。在您的情况下，您可以使用"扩展Rcpp"小插曲中最简单的解决方案：RCPP_EXPOSED_CLASS当你包括Rcpp:的哪个标题时，你只需要小心

#include <Rcpp.h>
class MyData
{
public:
MyData() = default;
};
RCPP_EXPOSED_CLASS(MyData)
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... " << std::endl; };
};
// Expose MyData
RCPP_MODULE(MyData){
Rcpp::class_<MyData>("MyData")
.constructor()
;
}
// Expose MyModel
RCPP_MODULE(MyModel){
Rcpp::class_<MyModel>("MyModel")
.constructor()
.method("train", &MyModel::train)
;
}
/***R
myData <- new(MyData)
myModel <- new(MyModel)
myModel$train(myData) 
*/

正如您在回答中所发现的，这甚至在之后有效，包括Rcpp.h。不过，浏览一下提到的画廊文章和小插曲还是有意义的。

首先，我应该指出问题中的示例过于简单。实际上，MyData类有一个类似void fill(const Rcpp::NumericMatrix& dat) { Rcpp::Rcout << "filling data... " << std::endl; };的方法，它依赖于Rcpp::NumericMatrix，所以在声明MyData之前，我必须#include <Rcpp.h>。

以下是我找到的两个解决方案，但我还没有充分使用它们来了解是否存在"陷阱"。

解决方案1-RCPP_EXPOSED_CLASS()宏

在这里，我使用了Romain Francois描述的RCPP_EXPOSED_CLASS()宏。(感谢拉尔夫向我指出这个金块。)

#include <Rcpp.h>
class MyData;
class MyModel;
RCPP_EXPOSED_CLASS(MyData)
RCPP_EXPOSED_CLASS(MyModel)
class MyData
{
public:
MyData() = default;
void fill(const Rcpp::NumericMatrix& dat) { Rcpp::Rcout << "filling data... " << std::endl; };
};
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... " << std::endl; };
};

// Expose MyData
RCPP_MODULE(MyData){
Rcpp::class_<MyData>("MyData")
.constructor()
.method("fill", &MyData::fill)
;
}
// Expose MyModel
RCPP_MODULE(MyModel){
Rcpp::class_<MyModel>("MyModel")
.constructor()
.method("train", &MyModel::train)
;
}
/***R
myData <- new(MyData)
myModel <- new(MyModel)
myModel$train(myData)
*/

解决方案2-使用Rcpp:：XPtr

此解决方案基于此处讨论的设计模式。基本上，我只是创建一个指向C++对象的指针，并使用包装器函数来处理它。

#include <Rcpp.h>
class MyData
{
public:
MyData() = default;
void fill(const Rcpp::NumericMatrix& dat) { Rcpp::Rcout << "filling data... " << std::endl; };
};
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... " << std::endl; };
};
// [[Rcpp::export]]
SEXP make_dataset() {
MyData* datPtr = new MyData();
Rcpp::XPtr<MyData> datXPtr(datPtr);
return datXPtr;
}
// [[Rcpp::export]]
SEXP make_model() {
MyModel* mdlPtr = new MyModel();
Rcpp::XPtr<MyModel> mdlXPtr(mdlPtr);
return mdlXPtr;
}
// [[Rcpp::export]]
void train_model(SEXP mdlXPtr, SEXP datXPtr) {
Rcpp::XPtr<MyModel> mdlPtr(mdlXPtr);
Rcpp::XPtr<MyData> datPtr(datXPtr);
mdlPtr->train(*datPtr);
}
/***R
myData <- make_dataset()
myModel <- make_model()
train_model(myModel, myData)
*/

这种方法的缺点是，AFAIK，没有一种明显的方法来检查XPtr指向的对象的类型。例如，我不清楚如何使train_model(myData, myModel)等坏调用无效。

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