Add missing read only implementation for x.at("name")

NEWS.md

@@ -1,5 +1,8 @@
 # cpp11 (development version)
 
+* Added the missing implementation for `x.at("name")` for read only vectors
+  (#370).
+
 * Constructors for writable vectors from `initializer_list<named_arg>` now
   check that `named_arg` contains a length 1 object of the correct type, and
   throws either a `cpp11::type_error` or `std::length_error` if that is not the

cpp11test/src/test-doubles.cpp

@@ -495,13 +495,21 @@ context("doubles-C++") {
     cpp11::writable::doubles x({"a"_nm = 1., "b"_nm = 2.});
     cpp11::doubles y(x);
 
-    expect_true(x["a"] == 1);
-    expect_true(x["b"] == 2);
-    expect_error(x["c"] == 2);
+    expect_true(x["a"] == 1.);
+    expect_true(x["b"] == 2.);
+    expect_error(x["c"]);
+
+    expect_true(x.at("a") == 1.);
+    expect_true(x.at("b") == 2.);
+    expect_error(x.at("c"));
+
+    expect_true(y["a"] == 1.);
+    expect_true(y["b"] == 2.);
+    expect_error(y["c"]);
 
-    expect_true(y["a"] == 1);
-    expect_true(y["b"] == 2);
-    expect_error(y["c"] == 2);
+    expect_true(y.at("a") == 1.);
+    expect_true(y.at("b") == 2.);
+    expect_error(y.at("c"));
   }
 
   test_that("doubles::find") {

cpp11test/src/test-integers.cpp

@@ -250,18 +250,26 @@ context("integers-C++") {
   }
 #endif
 
-  test_that("operator[] with names") {
+  test_that("operator[] and at with names") {
     using namespace cpp11::literals;
     cpp11::writable::integers x({"a"_nm = 1, "b"_nm = 2});
     cpp11::integers y(x);
 
     expect_true(x["a"] == 1);
     expect_true(x["b"] == 2);
-    expect_error(x["c"] == 2);
+    expect_error(x["c"]);
+
+    expect_true(x.at("a") == 1);
+    expect_true(x.at("b") == 2);
+    expect_error(x.at("c"));
 
     expect_true(y["a"] == 1);
     expect_true(y["b"] == 2);
-    expect_error(y["c"] == 2);
+    expect_error(y["c"]);
+
+    expect_true(y.at("a") == 1);
+    expect_true(y.at("b") == 2);
+    expect_error(y.at("c"));
   }
 
   test_that("is_na(integer)") {

cpp11test/src/test-list.cpp

@@ -168,7 +168,7 @@ context("list-C++") {
     expect_true(x.size() == nms.size());
   }
 
-  test_that("list::operator[] by name") {
+  test_that("list::operator[] and at by name") {
     SEXP x = PROTECT(Rf_allocVector(VECSXP, 1));
 
     SEXP elt = Rf_allocVector(INTSXP, 1);
@@ -183,9 +183,11 @@ context("list-C++") {
 
     expect_true(lst.named());
     expect_true(lst["name"] == elt);
+    expect_true(lst.at("name") == elt);
 
     // Lists are the only class where OOB accesses by name return `NULL`
     expect_true(lst["oob"] == R_NilValue);
+    expect_true(lst.at("oob") == R_NilValue);
 
     UNPROTECT(1);
   }

inst/include/cpp11/r_vector.hpp

@@ -502,6 +502,11 @@ inline T r_vector<T>::at(const size_type pos) const {
   return at(static_cast<R_xlen_t>(pos));
 }
 
+template <typename T>
+inline T r_vector<T>::at(const r_string& name) const {
+  return operator[](name);
+}
+
 template <typename T>
 inline bool r_vector<T>::contains(const r_string& name) const {
   SEXP names = this->names();