Support DynamicConverter conversions to dynamic

Summary: Allow conversions to types containing a `dynamic`.

Reviewed By: yfeldblum

Differential Revision: D33823657

fbshipit-source-id: b09537639efad185114dfd5953c1707207ddfcdf

folly/DynamicConverter.h

@@ -181,6 +181,12 @@ inline std::move_iterator<Transformer<T, It>> conversionIterator(const It& it) {
 template <typename T, typename Enable = void>
 struct DynamicConverter;
 
+// dynamic
+template <>
+struct DynamicConverter<dynamic> {
+  static dynamic convert(const dynamic& d) { return d; }
+};
+
 // boolean
 template <>
 struct DynamicConverter<bool> {

folly/test/DynamicConverterTest.cpp

@@ -71,6 +71,23 @@ TEST(DynamicConverter, template_metaprogramming) {
   EXPECT_EQ(r2t, true);
 }
 
+TEST(DynamicConverter, dynamics) {
+  dynamic d1 = 12;
+  auto d2 = convertTo<dynamic>(d1);
+  EXPECT_EQ(12, d2.getInt());
+
+  dynamic d3 = dynamic::array(1, 2, 3);
+  auto v = convertTo<std::vector<dynamic>>(d3);
+  EXPECT_EQ(1, v.at(0).getInt());
+  EXPECT_EQ(2, v.at(1).getInt());
+  EXPECT_EQ(3, v.at(2).getInt());
+
+  dynamic d4 = dynamic::object("1", 1)("2", 2.3);
+  auto m = convertTo<std::map<std::string, dynamic>>(d4);
+  EXPECT_EQ(1, m.at("1").getInt());
+  EXPECT_EQ(2.3, m.at("2").getDouble());
+}
+
 TEST(DynamicConverter, arithmetic_types) {
   dynamic d1 = 12;
   auto i1 = convertTo<int>(d1);