Add heterogenous operations in dynamic::setDefault

Summary:
dynamic::setDefault already calls heterogenous `emplace(...)`, however it does not behave correctly for static constexpr strings.
Add a specialization for StringPiece which solves this.

The current set of tests does not invoke setDefault with an object as a key.
This diffs adds a test that does that.

Reviewed By: shixiao

Differential Revision: D10007262

fbshipit-source-id: 386a44bf6b0a24f81e843695d177d85b280b907d

folly/dynamic-inl.h

@@ -671,24 +671,46 @@ inline dynamic&& dynamic::operator[](StringPiece k) && {
   return std::move((*this)[k]);
 }
 
-template <class K, class V>
-inline dynamic& dynamic::setDefault(K&& k, V&& v) {
+template <typename K, typename V>
+dynamic::IfIsNonStringDynamicConvertible<K, dynamic&> dynamic::setDefault(
+    K&& k,
+    V&& v) {
   auto& obj = get<ObjectImpl>();
   return obj.emplace(std::forward<K>(k), std::forward<V>(v)).first->second;
 }
 
-template <class K>
-inline dynamic& dynamic::setDefault(K&& k, dynamic&& v) {
+template <typename K>
+dynamic::IfIsNonStringDynamicConvertible<K, dynamic&> dynamic::setDefault(
+    K&& k,
+    dynamic&& v) {
   auto& obj = get<ObjectImpl>();
   return obj.emplace(std::forward<K>(k), std::move(v)).first->second;
 }
 
-template <class K>
-inline dynamic& dynamic::setDefault(K&& k, const dynamic& v) {
+template <typename K>
+dynamic::IfIsNonStringDynamicConvertible<K, dynamic&> dynamic::setDefault(
+    K&& k,
+    const dynamic& v) {
   auto& obj = get<ObjectImpl>();
   return obj.emplace(std::forward<K>(k), v).first->second;
 }
 
+template <typename V>
+dynamic& dynamic::setDefault(StringPiece k, V&& v) {
+  auto& obj = get<ObjectImpl>();
+  return obj.emplace(k, std::forward<V>(v)).first->second;
+}
+
+inline dynamic& dynamic::setDefault(StringPiece k, dynamic&& v) {
+  auto& obj = get<ObjectImpl>();
+  return obj.emplace(k, std::move(v)).first->second;
+}
+
+inline dynamic& dynamic::setDefault(StringPiece k, const dynamic& v) {
+  auto& obj = get<ObjectImpl>();
+  return obj.emplace(k, v).first->second;
+}
+
 template <typename K>
 dynamic::IfIsNonStringDynamicConvertible<K, dynamic const*> dynamic::get_ptr(
     K&& k) const& {

folly/dynamic.h

@@ -502,16 +502,25 @@ struct dynamic : private boost::operators<dynamic> {
   dynamic getDefault(const dynamic& k, dynamic&& v) const&;
   dynamic getDefault(const dynamic& k, const dynamic& v = dynamic::object) &&;
   dynamic getDefault(const dynamic& k, dynamic&& v) &&;
-  template <class K, class V>
-  dynamic& setDefault(K&& k, V&& v);
+
+  template <typename K, typename V>
+  IfIsNonStringDynamicConvertible<K, dynamic&> setDefault(K&& k, V&& v);
+
+  template <typename V>
+  dynamic& setDefault(StringPiece k, V&& v);
   // MSVC 2015 Update 3 needs these extra overloads because if V were a
   // defaulted template parameter, it causes MSVC to consider v an rvalue
   // reference rather than a universal reference, resulting in it not being
   // able to find the correct overload to construct a dynamic with.
-  template <class K>
-  dynamic& setDefault(K&& k, dynamic&& v);
-  template <class K>
-  dynamic& setDefault(K&& k, const dynamic& v = dynamic::object);
+  template <typename K>
+  IfIsNonStringDynamicConvertible<K, dynamic&> setDefault(K&& k, dynamic&& v);
+  template <typename K>
+  IfIsNonStringDynamicConvertible<K, dynamic&> setDefault(
+      K&& k,
+      const dynamic& v = dynamic::object);
+
+  dynamic& setDefault(StringPiece k, dynamic&& v);
+  dynamic& setDefault(StringPiece k, const dynamic& v = dynamic::object);
 
   /*
    * Resizes an array so it has at n elements, using the supplied

folly/test/DynamicTest.cpp

@@ -504,6 +504,17 @@ TEST(Dynamic, GetSetDefaultTest) {
   dynamic d4 = dynamic::array;
   EXPECT_ANY_THROW(d4.getDefault("foo", "bar"));
   EXPECT_ANY_THROW(d4.setDefault("foo", "bar"));
+
+  // Using dynamic keys
+  dynamic k10{10}, k20{20}, kTrue{true};
+  dynamic d5 = dynamic::object(k10, "foo");
+  EXPECT_EQ(d5.setDefault(k10, "bar"), "foo");
+  EXPECT_EQ(d5.setDefault(k20, "bar"), "bar");
+  EXPECT_EQ(d5.setDefault(kTrue, "baz"), "baz");
+  EXPECT_EQ(d5.setDefault(StaticStrings::kA, "foo"), "foo");
+  EXPECT_EQ(d5.setDefault(StaticStrings::kB, "foo"), "foo");
+  EXPECT_EQ(d5.setDefault(StaticStrings::kFoo, "bar"), "bar");
+  EXPECT_EQ(d5.setDefault(StaticStrings::kBar, "foo"), "foo");
 }
 
 TEST(Dynamic, ObjectForwarding) {