Enhance Rcpp::Nullable::as with explicit cast (Closes #1470) (#1471)

* Enhance Rcpp::Nullable::as with explicit cast (Closes #1470)

* Add operator T

* Conditrion nullable<String> test on R 4.3.0 or later

* Move the conditional to operator T()

* Hide Nullable::operatorT() behind a #define

This passes reverse-dependency checks

Author: eddelbuettel

ChangeLog

@@ -1,6 +1,18 @@
+2026-04-12  Dirk Eddelbuettel  <edd@debian.org>
+
+	* inst/include/Rcpp/Nullable.h (Nullable): 'operator T()' is now
+	behind an opt-in #define
+
 2026-04-09  Dirk Eddelbuettel  <edd@debian.org>
 
 	* DESCRIPTION (Version, Date): Roll micro version and date
+	* inst/include/Rcpp/Nullable.h (T): Also add 'operator T()'
+	(conditional on R (>= 4.3.0) as older versions croak)
+
+2026-04-08  Dirk Eddelbuettel  <edd@debian.org>
+
+	* inst/include/Rcpp/Nullable.h (as): Enhance by adding an explicit
+	Rcpp::as<T>() aiding cases where implicit as<> does not suffice
 
 2026-04-07  Dirk Eddelbuettel  <edd@debian.org>
 

inst/include/Rcpp/Nullable.h

@@ -81,6 +81,18 @@ namespace Rcpp {
             return m_sexp;
         }
 
+#if R_VERSION > R_Version(4,3,0) && defined(RCPP_ENABLE_NULLABLE_T)
+        /**
+         * operator T() to return nullable object
+         *
+         * @throw 'not initialized' if object has not been set
+         */
+        inline operator T() const {
+            checkIfSet();
+            return Rcpp::as<T>(m_sexp);
+        }
+#endif
+
         /**
          * get() accessor for object
          *
@@ -126,7 +138,7 @@ namespace Rcpp {
         /**
          * Returns m_sexp as a T
          */
-        inline T as() { return get(); }
+        inline T as() { return Rcpp::as<T>(get()); }
 
         /**
          * Return a clone of m_sexp as a T

inst/tinytest/test_misc.R

@@ -168,7 +168,7 @@ expect_equal( testNullableIsUsable(M), M)
 #    test.NullableIsUsableFalse <- function() {
 expect_true(is.null(testNullableIsUsable(NULL)))
 
-#    test.NullableString <- function() {
+##    test.NullableString <- function() {
 expect_equal(testNullableString(), "")
 expect_equal(testNullableString("blah"), "blah")