draft map -> list/sexp

Author: pachadotdev

cpp11test/DESCRIPTION

@@ -20,4 +20,4 @@ Suggests:
     xml2
 LazyData: true
 Roxygen: list(markdown = TRUE)
-RoxygenNote: 7.1.1
+RoxygenNote: 7.3.2

inst/include/cpp11/map_to_sexp.hpp

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <map>
+#include <unordered_map>
+#include "cpp11/R.hpp"
+#include "cpp11/protect.hpp"
+#include "cpp11/list.hpp"
+#include "cpp11/strings.hpp"
+
+namespace cpp11 {
+
+template <typename Key, typename Value>
+SEXP map_to_sexp(const std::map<Key, Value>& map) {
+  cpp11::writable::list result(map.size());
+  cpp11::writable::strings names(map.size());
+
+  size_t i = 0;
+  for (const auto& pair : map) {
+    result[i] = cpp11::as_sexp(pair.second);
+    names[i] = cpp11::as_sexp(pair.first);
+    ++i;
+  }
+
+  result.names() = names;
+  return result;
+}
+
+template <typename Key, typename Value>
+SEXP unordered_map_to_sexp(const std::unordered_map<Key, Value>& map) {
+  cpp11::writable::list result(map.size());
+  cpp11::writable::strings names(map.size());
+
+  size_t i = 0;
+  for (const auto& pair : map) {
+    result[i] = cpp11::as_sexp(pair.second);
+    names[i] = cpp11::as_sexp(pair.first);
+    ++i;
+  }
+
+  result.names() = names;
+  return result;
+}
+
+}  // namespace cpp11

vignettes/motivations.Rmd

@@ -332,7 +332,52 @@ Doing this universally avoids many locale specific issues when dealing with Unic
 
 Concretely cpp11 always uses `Rf_translateCharUTF8()` when obtaining `const char*` from `CHRSXP` objects and uses `Rf_mkCharCE(, CE_UTF8)` when creating new `CHRSXP` objects from `const char*` inputs.
 
-<!--TODO: unicode examples?-->
+Converting R Unicode Strings to C++ Strings:
+
+```cpp
+#include <cpp11.hpp>
+#include <string>
+
+[[cpp11::register]]
+std::string convert_to_utf8(cpp11::strings input) {
+  std::string result;
+  for (auto str : input) {
+    result += cpp11::r_string(Rf_translateCharUTF8(str));
+  }
+  return result;
+}
+```
+
+```r
+# hello + how are you? in Japanese and Spanish
+input <- c("\xe3\x81\x93\xe3\x82\x93\xe3\x81\xab\xe3\x81\xa1\xe3\x81\xaf",
+  "\xc2\xbfC\xc3\xb3mo est\xc3\xa1s\x3f")
+
+convert_to_utf8(input)
+
+[1] "こんにちは¿Cómo estás?"
+```
+
+Returning Unicode Strings from C++ to R:
+
+```cpp
+#include <cpp11.hpp>
+#include <string>
+
+[[cpp11::register]]
+cpp11::writable::strings return_utf8_string() {
+  cpp11::writable::strings result;
+  std::string utf8_str = "こんにちは"; // Hello in Japanese
+  result.push_back(Rf_mkCharCE(utf8_str.c_str(), CE_UTF8));
+  return result;
+}
+```
+
+```r
+return_utf8_string()
+
+[1] "こんにちは"
+```
 
 ## C++11 features {#c11-features}