Merge pull request #1082 from RcppCore/bugfix/string-preserve-fixes

remove erroneous PreserveObject call in String::wrap

Author: eddelbuettel

ChangeLog

@@ -1,3 +1,8 @@
+2020-05-17  Kevin Ushey  <kevinushey@gmail.com>
+
+	* inst/include/Rcpp/String.h: don't preserve returned SEXP in wrap
+	* inst/include/RcppCommon.h: simplify
+
 2020-04-30  Dirk Eddelbuettel  <edd@debian.org>
 
         * DESCRIPTION (Version, Date): Roll minor version

inst/include/Rcpp/String.h

@@ -532,7 +532,6 @@ namespace Rcpp {
         RCPP_STRING_DEBUG("wrap<String>()");
         Shield<SEXP> res(Rf_allocVector(STRSXP, 1));
         SEXP data = object.get_sexp();
-        Rcpp_PreserveObject(data);
         SET_STRING_ELT(res, 0, data);
         return res;
     }

inst/include/RcppCommon.h

@@ -101,22 +101,13 @@ namespace Rcpp {
     }
 
     inline SEXP Rcpp_ReplaceObject(SEXP x, SEXP y) {
-        if (Rf_isNull(x)) {
-            Rcpp_PreserveObject(y);
-        } else if (Rf_isNull(y)) {
-            Rcpp_ReleaseObject(x); 	// #nocov
-        } else {
-            // if we are setting to the same SEXP as we already have, do nothing
-            if (x != y) {
-
-                // the previous SEXP was not NULL, so release it
-                Rcpp_ReleaseObject(x);
-
-                // the new SEXP is not NULL, so preserve it
-                Rcpp_PreserveObject(y);
 
-            }
+        // if we are setting to the same SEXP as we already have, do nothing
+        if (x != y) {
+            Rcpp_ReleaseObject(x);
+            Rcpp_PreserveObject(y);
         }
+
         return y;
     }