Names of named args in list are now resized along with list elements

NEWS.md

@@ -5,6 +5,7 @@
 * Error messages now output original file name rather than the temporary file name (@sbearrows, #194)
 * Fixed bug when running `cpp_source()` on the same file more than once (@sbearrows, #202)
 * Removed internal instances of `cpp11::stop()` and replaced with C++ exceptions (@sbearrows, #203)
+* Names of named lists are now resized along with the list elements (@sbearrows, #206)
 * Added optionally formatting to `stop()` and `warning()` using {fmt} library (@sbearrows, #169)
 
 # cpp11 0.3.1

cpp11test/src/test-list.cpp

@@ -141,4 +141,17 @@ context("list-C++") {
 
     expect_false(y.empty());
   }
+
+  test_that("names of named lists are also resized") {
+    cpp11::writable::list x;
+    x.push_back({"n1"_nm = 1});
+    x.push_back({"n2"_nm = 2});
+    x.push_back({"n3"_nm = 3});
+    x.push_back({"n4"_nm = 4});
+    x.push_back({"n5"_nm = 5});
+    x = SEXP(x);
+
+    cpp11::strings nms(x.names());
+    expect_true(x.size() == nms.size());
+  }
 }

inst/include/cpp11/r_vector.hpp

@@ -878,17 +878,28 @@ inline void r_vector<T>::clear() {
   length_ = 0;
 }
 
+inline SEXP truncate(SEXP x, R_xlen_t length, R_xlen_t capacity) {
+#if R_VERSION >= R_Version(3, 4, 0)
+  SETLENGTH(x, length);
+  SET_TRUELENGTH(x, capacity);
+  SET_GROWABLE_BIT(x);
+#else
+  x = safe[Rf_lengthgets](x, length_);
+#endif
+  return x;
+}
+
 template <typename T>
 inline r_vector<T>::operator SEXP() const {
   if (length_ < capacity_) {
-#if R_VERSION >= R_Version(3, 4, 0)
-    SETLENGTH(data_, length_);
-    SET_TRUELENGTH(data_, capacity_);
-    SET_GROWABLE_BIT(data_);
-#else
     auto* p = const_cast<r_vector<T>*>(this);
-    p->data_ = safe[Rf_lengthgets](data_, length_);
-#endif
+    p->data_ = truncate(p->data_, length_, capacity_);
+    SEXP nms = names();
+    auto nms_size = Rf_xlength(nms);
+    if ((nms_size > 0) && (length_ < nms_size)) {
+      nms = truncate(nms, length_, capacity_);
+      names() = nms;
+    }
   }
   return data_;
 }