Added Nullable::isUsable() function

Author: dcdillon

inst/include/Rcpp/Nullable.h

@@ -91,6 +91,13 @@ namespace Rcpp {
             return m_sexp;
         }
 
+        /**
+         * Boolean test for usability as a T
+         */
+        inline bool isUsable() const {
+            return m_set && !Rf_isNull(m_sexp);
+        }
+
         /**
          * Boolean test for NULL
          *

inst/unitTests/cpp/misc.cpp

@@ -207,3 +207,12 @@ NumericMatrix testNullableAs(Nullable<NumericMatrix>& M) {
 NumericMatrix testNullableClone(const Nullable<NumericMatrix>& M) {
     return M.clone();
 }
+
+// [[Rcpp::export]]
+SEXP testNullableIsUsable(const Nullable<NumericMatrix>& M) {
+    if (M.isUsable()) {
+        return M.clone();
+    } else {
+        return R_NilValue;
+    }
+}

inst/unitTests/runit.misc.R

@@ -195,4 +195,13 @@ if (.runThisTest) {
         M <- matrix(1:4, 2, 2)
         checkEquals( testNullableClone(M), M )
     }
+
+    test.NullableIsUsableTrue <- function() {
+	M <- matrix(1:4, 2, 2)
+        checkEquals( testNullableIsUsable(M), M)
+    }
+
+    test.NullableIsUsableFalse <- function() {
+        checkTrue(is.null(testNullableIsUsable(NULL)))
+    }
 }