Simplify attribute accessor using two lambda visitors

ChangeLog

@@ -1,16 +1,12 @@
 2025-12-22  Dirk Eddelbuettel  <edd@debian.org>
 
 	* inst/include/Rcpp/DataFrame.h (nrow): Simplified per #1430 discussion
-	relying on compact sequence also removing use of ATTRIB
+	relying on compact sequence representation removing use of ATTRIB
+	* inst/include/Rcpp/proxy/AttributeProxy.h (hasAttribute): For R
+	4.6.0, rewritten using R_mapAttrib() avoiding to-be-removed ATTRIB()
 
 2025-12-21  Dirk Eddelbuettel  <edd@debian.org>
 
-	* inst/include/Rcpp/proxy/AttributeProxy.h (attributeNames):
-	Rewritten using R_mapAttrib() avoiding ATTRIB() to be removed in R 4.6.0
-	* src/utilities.cpp: Add helper function used by R_mapAttrib()
-	* inst/include/Rcpp/routines.h: Register new helper function
-	* src/rcpp_init.cpp (registerFunctions): Idem
-
 	* .github/workflows/docker.yaml: Add workflow_dispatch, update
 	checkout action
 

inst/include/Rcpp/DataFrame.h

@@ -62,17 +62,13 @@ namespace Rcpp{
 
         // By definition, the number of rows in a data.frame is contained
         // in its row.names attribute. Since R 3.5.0 this is returned as a
-        // compact sequence from which we can just take the length
-        //   Shield<SEXP> rn = Rf_getAttrib(Parent::get__(), R_RowNamesSymbol);
-        //   return Rf_xlength(rn);
+        // compact sequence from which we can just take the (x)length
         // But as this makes an allocation an even simpler check on length as
         // discussed in #1430 is also possible and preferable. We also switch
         // to returning R_xlen_t which as upcast from int is safe
         inline R_xlen_t nrow() const {
-            SEXP x = Parent::get__();
-            // We can simplify: zero row DFs have no names, else length of all vector same
-            // by design constraint so can use vector length for desired row count
-            return (XLENGTH(x) == 0) ? 0 : XLENGTH(VECTOR_ELT(x, 0));
+            Shield<SEXP> rn = Rf_getAttrib(Parent::get__(), R_RowNamesSymbol);
+            return Rf_xlength(rn);
         }
 
         template <typename T>

inst/include/Rcpp/proxy/AttributeProxy.h

@@ -80,22 +80,42 @@ class AttributeProxyPolicy {
     std::vector<std::string> attributeNames() const {
         std::vector<std::string> v;
 #if R_VERSION >= R_Version(4, 6, 0)
-        R_mapAttrib(static_cast<const CLASS&>(*this).get__(), get_attr_names, (void *) &v);
+        auto visitor = [](SEXP name, SEXP attr, void* data) -> SEXP {
+            std::vector<std::string>* ptr = static_cast<std::vector<std::string>*>(data);
+            std::string s{CHAR(Rf_asChar(name))};
+            ptr->push_back(s);
+            return NULL;
+        };
+        R_mapAttrib(static_cast<const CLASS&>(*this).get__(), visitor, static_cast<void*>(&v));
 #else
         SEXP attrs = ATTRIB( static_cast<const CLASS&>(*this).get__());
         while( attrs != R_NilValue ){
             v.push_back( std::string(CHAR(PRINTNAME(TAG(attrs)))) ) ;
             attrs = CDR( attrs ) ;
         }
 #endif
-        return v ;
+        return v;
     }
 
-    bool hasAttribute( const std::string& attr) const {
+    struct AttributeProxyStruct {
+        const std::string* match;
+        bool found;
+    };
+
+    bool hasAttribute(const std::string& attr) const {
 #if R_VERSION >= R_Version(4, 6, 0)
-        std::vector<std::string> v = attributeNames();
-        auto it = std::find(v.begin(), v.end(), attr);
-        return it != v.end();   // if found 'it' points to element equal to 'attr'
+        auto visitor = [](SEXP name, SEXP attr, void* data) -> SEXP {
+            AttributeProxyStruct *ptr = static_cast<struct AttributeProxyStruct*>(data);
+            if (ptr->found) return Rf_ScalarInteger(1); 	// already found
+            if (*(ptr->match) == CHAR(Rf_asChar(name))) {
+                ptr->found = true; 							// signal we have match
+                return Rf_ScalarInteger(1);
+            }
+            return NULL;           							// continue
+        };
+        AttributeProxyStruct str{&attr, false};
+        R_mapAttrib(static_cast<const CLASS&>(*this).get__(), visitor, static_cast<void*>(&str));
+        return str.found;
 #else
         SEXP attrs = ATTRIB(static_cast<const CLASS&>(*this).get__());
         while( attrs != R_NilValue ){

inst/include/Rcpp/routines.h

@@ -74,8 +74,6 @@ SEXP          reset_current_error();
 int           error_occured();
 SEXP          rcpp_get_current_error();
 // void          print(SEXP s);
-SEXP          get_attr_names(SEXP t, SEXP a, void* d);
-SEXP          get_row_count(SEXP t, SEXP a, void* d);
 
 #else
 
@@ -311,12 +309,6 @@ inline attribute_hidden SEXP rcpp_get_current_error(){
 //     fun(s);
 // }
 
-inline attribute_hidden SEXP get_attr_names(SEXP tag, SEXP attr, void* data){
-    typedef SEXP (*Fun)(SEXP, SEXP, void*);
-    static Fun fun = GET_CALLABLE("get_attr_names");
-    return fun(tag, attr, data);
-}
-
 #endif
 
 

src/rcpp_init.cpp

@@ -127,8 +127,6 @@ void registerFunctions(){
     RCPP_REGISTER(Rcpp_precious_remove)
     RCPP_REGISTER(Rcpp_cout_get)
     RCPP_REGISTER(Rcpp_cerr_get)
-
-    RCPP_REGISTER(get_attr_names)
     #undef RCPP_REGISTER
 }