Fixing issue with Rcpp::String and Rcpp::Nullable

Author: Daniel C. Dillon

inst/include/Rcpp/String.h

@@ -71,16 +71,35 @@ namespace Rcpp {
         }
 
         /** construct a string from a single CHARSXP SEXP */
-        String(SEXP charsxp) : data(charsxp), valid(true), buffer_ready(false), enc(Rf_getCharCE(charsxp)) {
+        String(SEXP charsxp) : data(R_NilValue) {
+            if (TYPEOF(charsxp) == STRSXP) {
+                data = STRING_ELT(charsxp, 0);
+            } else if (TYPEOF(charsxp) == CHARSXP) {
+                data = charsxp;
+            }
+
             if (::Rf_isString(data) && ::Rf_length(data) != 1)
                 throw ::Rcpp::not_compatible("expecting a single value");
+
+            valid = true;
+            buffer_ready = false;
+            enc = Rf_getCharCE(data);
             Rcpp_PreserveObject(data);
             RCPP_STRING_DEBUG("String(SEXP)");
         }
 
-        String(SEXP charsxp, const std::string& enc) : data(charsxp), valid(true), buffer_ready(false) {
+        String(SEXP charsxp, const std::string& enc) : data(R_NilValue) {
+            if (TYPEOF(charsxp) == STRSXP) {
+                data = STRING_ELT(charsxp, 0);
+            } else if (TYPEOF(charsxp) == CHARSXP) {
+                data = charsxp;
+            }
+
             if (::Rf_isString(data) && ::Rf_length(data) != 1)
                 throw ::Rcpp::not_compatible("expecting a single value");
+
+            valid = true;
+            buffer_ready = false;
             Rcpp_PreserveObject(data);
             set_encoding(enc);
             RCPP_STRING_DEBUG("String(SEXP)");

inst/unitTests/cpp/misc.cpp

@@ -216,3 +216,11 @@ SEXP testNullableIsUsable(const Nullable<NumericMatrix>& M) {
         return R_NilValue;
     }
 }
+
+// [[Rcpp::export]]
+String testNullableString(Rcpp::Nullable<Rcpp::String> param = R_NilValue) {
+  if (param.isNotNull())
+    return String(param);
+  else
+    return String("");
+}

inst/unitTests/runit.misc.R

@@ -204,4 +204,9 @@ if (.runThisTest) {
     test.NullableIsUsableFalse <- function() {
         checkTrue(is.null(testNullableIsUsable(NULL)))
     }
+
+    test.NullableString <- function() {
+        checkEquals(testNullableString(), "")
+        checkEquals(testNullableString("blah"), "blah")
+    }
 }