generalize sapply solution to get result_of functions

Author: Enchufa2

inst/include/Rcpp/sugar/functions/sapply.h

@@ -1,7 +1,8 @@
 
 // sapply.h: Rcpp R/C++ interface class library -- sapply
 //
-// Copyright (C) 2010 - 2023 Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2010 - 2024 Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2025        Dirk Eddelbuettel, Romain Francois and Iñaki Ucar
 //
 // This file is part of Rcpp.
 //
@@ -27,36 +28,16 @@
 namespace Rcpp{
 namespace sugar{
 
-template <typename Function, typename SugarExpression>
-struct sapply_application_result_of
-{
-#if __cplusplus >= 201103L
-    #if __cplusplus < 201703L
-        // deprecated by C++17, removed by C++2020, see https://en.cppreference.com/w/cpp/types/result_of
- 	    typedef typename ::std::result_of<Function(typename SugarExpression::stored_type)>::type type;
-    #else
-        // since C++17, see https://en.cppreference.com/w/cpp/types/result_of
-        typedef typename ::std::invoke_result<Function, typename SugarExpression::stored_type>::type type;
-    #endif
-#else
-    // TODO this else branch can likely go
-	typedef typename ::Rcpp::traits::result_of<Function>::type type;
-#endif
-};
-
-// template <typename Function, typename SugarExpression>
-// using sapply_application_result_of_t = typename sapply_application_result_of<Function, SugarExpression>::type;
-
 template <int RTYPE, bool NA, typename T, typename Function, bool NO_CONVERSION>
 class Sapply : public VectorBase<
 	Rcpp::traits::r_sexptype_traits<
-		typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type
+		typename ::Rcpp::traits::result_of<Function, T>::type
 	>::rtype ,
 	true ,
 	Sapply<RTYPE,NA,T,Function,NO_CONVERSION>
 > {
 public:
-	typedef typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type result_type ;
+	typedef typename ::Rcpp::traits::result_of<Function, T>::type result_type ;
 	const static int RESULT_R_TYPE =
 		Rcpp::traits::r_sexptype_traits<result_type>::rtype ;
 
@@ -87,13 +68,13 @@ class Sapply : public VectorBase<
 template <int RTYPE, bool NA, typename T, typename Function>
 class Sapply<RTYPE,NA,T,Function,true> : public VectorBase<
 	Rcpp::traits::r_sexptype_traits<
-		typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type
+		typename ::Rcpp::traits::result_of<Function, T>::type
 	>::rtype ,
 	true ,
 	Sapply<RTYPE,NA,T,Function,true>
 > {
 public:
-	typedef typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type result_type ;
+	typedef typename ::Rcpp::traits::result_of<Function, T>::type result_type ;
 	const static int RESULT_R_TYPE =
 		Rcpp::traits::r_sexptype_traits<result_type>::rtype ;
 
@@ -124,15 +105,15 @@ template <int RTYPE, bool NA, typename T, typename Function >
 inline sugar::Sapply<
     RTYPE,NA,T,Function,
     traits::same_type<
-        typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type ,
-        typename Rcpp::traits::storage_type< traits::r_sexptype_traits< typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type >::rtype >::type
+        typename ::Rcpp::traits::result_of<Function, T>::type ,
+        typename Rcpp::traits::storage_type< traits::r_sexptype_traits< typename ::Rcpp::traits::result_of<Function, T>::type >::rtype >::type
     >::value
 >
 sapply( const Rcpp::VectorBase<RTYPE,NA,T>& t, Function fun ){
 	return sugar::Sapply<RTYPE,NA,T,Function,
 	traits::same_type<
-        typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type ,
-        typename Rcpp::traits::storage_type< traits::r_sexptype_traits< typename ::Rcpp::sugar::sapply_application_result_of<Function, T>::type >::rtype >::type
+        typename ::Rcpp::traits::result_of<Function, T>::type ,
+        typename Rcpp::traits::storage_type< traits::r_sexptype_traits< typename ::Rcpp::traits::result_of<Function, T>::type >::rtype >::type
     >::value >( t, fun ) ;
 }
 

inst/include/Rcpp/traits/result_of.h

@@ -3,7 +3,8 @@
 //
 // result_of.h: Rcpp R/C++ interface class library -- traits to help wrap
 //
-// Copyright (C) 2010 - 2012 Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2010 - 2024 Dirk Eddelbuettel and Romain Francois
+// Copyright (C) 2025        Dirk Eddelbuettel, Romain Francois, Iñaki Ucar
 //
 // This file is part of Rcpp.
 //
@@ -26,24 +27,20 @@
 namespace Rcpp{
 namespace traits{
 
-template <typename T>
+template <typename T, typename... Args>
 struct result_of{
-	typedef typename T::result_type type ;
-} ;
-
-template <typename RESULT_TYPE, typename INPUT_TYPE>
-struct result_of< RESULT_TYPE (*)(INPUT_TYPE) >{
-	typedef RESULT_TYPE type ;
-} ;
-
-template <typename RESULT_TYPE, typename U1, typename U2>
-struct result_of< RESULT_TYPE (*)(U1, U2) >{
-	typedef RESULT_TYPE type ;
+#if __cplusplus < 201703L
+    // deprecated by C++17, removed by C++2020, see https://en.cppreference.com/w/cpp/types/result_of
+    typedef typename ::std::result_of<T(typename Args::stored_type...)>::type type;
+#else
+    // since C++17, see https://en.cppreference.com/w/cpp/types/result_of
+    typedef typename ::std::invoke_result<T, typename Args::stored_type...>::type type;
+#endif
 } ;
 
-template <typename RESULT_TYPE, typename U1, typename U2, typename U3>
-struct result_of< RESULT_TYPE (*)(U1, U2, U3) >{
-	typedef RESULT_TYPE type ;
+template <typename T>
+struct result_of<T>{
+    typename T::result_type type ;
 } ;
 
 }