Ensure we call operator SEXP() when copying or moving writable vectors

The previous code was unintentially avoiding this call by copying the
`.data_` member directly.

Fixes #91

NEWS.md

@@ -1,5 +1,7 @@
 # cpp11 (development version)
 
+* `data_frame()` objects now have the number of rows correctly set as real length, not the reserved length (#91)
+
 # cpp11 0.2.1
 
 * Ensures backwards compatibility with code generation from cpp11 0.1.0 (#88)

cpp11test/src/test-data_frame.cpp

@@ -90,4 +90,17 @@ context("data_frame-C++") {
     expect_true(cpp11::integers(df["a"])[0] == 1);
     expect_true(cpp11::strings(df["b"])[2] == "c");
   }
+
+  test_that("growing vectors uses proper length") {
+    using namespace cpp11::literals;
+
+    cpp11::writable::integers x, y;
+    for (int i = 0; i < 10; ++i) {
+      x.push_back(i);
+      y.push_back(i);
+    }
+    cpp11::writable::data_frame out({"x"_nm = x, "y"_nm = y});
+
+    expect_true(out.nrow() == 10);
+  }
 }

inst/include/cpp11/r_vector.hpp

@@ -760,22 +760,20 @@ inline typename r_vector<T>::iterator r_vector<T>::find(const r_string& name) co
 
 template <typename T>
 inline r_vector<T>::r_vector(const r_vector<T>& rhs)
-    : cpp11::r_vector<T>(safe[Rf_shallow_duplicate](rhs.data_)),
+    : cpp11::r_vector<T>(safe[Rf_shallow_duplicate](rhs)),
       protect_(protect_sexp(data_)),
       capacity_(rhs.capacity_) {}
 
 template <typename T>
 inline r_vector<T>::r_vector(r_vector<T>&& rhs)
-    : cpp11::r_vector<T>(rhs.data_),
-      protect_(protect_sexp(data_)),
-      capacity_(rhs.capacity_) {
+    : cpp11::r_vector<T>(rhs), protect_(protect_sexp(data_)), capacity_(rhs.capacity_) {
   rhs.data_ = R_NilValue;
   rhs.protect_ = R_NilValue;
 }
 
 template <typename T>
 inline r_vector<T>::r_vector(const cpp11::r_vector<T>& rhs)
-    : cpp11::r_vector<T>(safe[Rf_shallow_duplicate](rhs.data_)),
+    : cpp11::r_vector<T>(safe[Rf_shallow_duplicate](rhs)),
       protect_(protect_sexp(data_)),
       capacity_(rhs.length_) {}