adding empty to vector classes

NEWS.md

@@ -1,5 +1,6 @@
 # cpp11 (development version)
 
+* Added `x.empty()` method to check if a vector is empty (@sbearrows, #182)
 * New `cpp11::na()` function to return the NA sentinals for R objects(@sbearrows, #179)
 * Incorrectly formatted cpp11 decorators now output a more informative error message (@sbearrows, #127)
 * Generated registration code now uses C collation to avoid spurious diffs from `tools::package_native_routine_registration_skeleton()` (@sbearrows, #171)

cpp11test/src/test-list.cpp

@@ -122,4 +122,14 @@ context("list-C++") {
     expect_true(first[0] == 1);
     expect_true(first[1] == 2);
   }
+
+  test_that("empty() works") {
+    cpp11::writable::list x;
+
+    expect_true(x.empty());
+
+    cpp11::writable::list y(1);
+
+    expect_false(y.empty());
+  }
 }

inst/include/cpp11/r_vector.hpp

@@ -112,6 +112,8 @@ class r_vector {
 
   operator sexp() const;
 
+  bool empty() const;
+
   /// Provide access to the underlying data, mainly for interface
   /// compatibility with std::vector
   SEXP data() const;
@@ -389,6 +391,11 @@ inline r_vector<T>::operator SEXP() const {
   return data_;
 }
 
+template <typename T>
+inline bool r_vector<T>::empty() const {
+  return (!(this->size() > 0));
+}
+
 template <typename T>
 inline r_vector<T>::operator sexp() const {
   return data_;