Adding DynamicConstructor specialization for enums

Summary:
A specialization for reading into enums from serialized form was added a while back. Unfortunately, no corresponding change to serialize from enums into a dynamic was added.

This change adds the corresponding DynamicConstructor specialization for enums to allow serializing enums and objects containing enums.

Reviewed By: ot, shixiao

Differential Revision: D14091417

fbshipit-source-id: 15ef8bc46843cd668b4b2c991e84167dabaf69fa

folly/DynamicConverter.h

@@ -328,6 +328,17 @@ struct DynamicConstructor<
   }
 };
 
+// enums
+template <typename C>
+struct DynamicConstructor<
+    C,
+    typename std::enable_if<std::is_enum<C>::value>::type> {
+  static dynamic construct(const C& x) {
+    using type = typename std::underlying_type<C>::type;
+    return dynamic(static_cast<type>(x));
+  }
+};
+
 // maps
 template <typename C>
 struct DynamicConstructor<

folly/test/DynamicConverterTest.cpp

@@ -386,6 +386,24 @@ TEST(DynamicConverter, construct) {
     dynamic d = dynamic::array(true, false);
     EXPECT_EQ(d, toDynamic(vb));
   }
+
+  {
+    enum enum1 { foo = 1, bar = 2 };
+
+    dynamic d1 = 1;
+    EXPECT_EQ(d1, toDynamic(enum1::foo));
+
+    dynamic d2 = 2;
+    EXPECT_EQ(d2, toDynamic(enum1::bar));
+
+    enum class enum2 : char { FOO = 'a', BAR = 'b' };
+
+    dynamic d3 = 'a';
+    EXPECT_EQ(d3, toDynamic(enum2::FOO));
+
+    dynamic d4 = 'b';
+    EXPECT_EQ(d4, toDynamic(enum2::BAR));
+  }
 }
 
 TEST(DynamicConverter, errors) {