Improve handling of member expressions

Summary:
In LRef differentiate between "by literal" and "by value" and handle the
latter more efficiently by simply remembering the property name.

Change the object value from an object pointer to a regular FNValue.

Use LRef in a couple of places instead of self.gen_prop(), which is now
unneeded and removed.

Add new object methods to FNObject: getByVal() and putByVal() taking
std::string for now.

Reviewed By: neildhar

Differential Revision: D37232324

fbshipit-source-id: e84868b60a3d729b25523129c491bb360a77c8c0

unsupported/juno/crates/flow_native/runtime/FNRuntime.cpp

@@ -11,16 +11,24 @@
 
 const FNString fn_prototype_str{"prototype"};
 
+FNValue FNObject::getByName(const std::string &key) {
+  auto *cur = this;
+  do {
+    auto it = cur->props.find(key);
+    if (it != cur->props.end())
+      return it->second;
+    cur = cur->parent;
+  } while (cur);
+  return FNValue::encodeUndefined();
+}
+
+void FNObject::putByName(const std::string &key, FNValue val) {
+  props[key] = val;
+}
+
 FNValue FNObject::getByVal(FNValue key) {
   if (key.isString()) {
-    auto *cur = this;
-    do {
-      auto it = cur->props.find(key.getString()->str);
-      if (it != cur->props.end())
-        return it->second;
-      cur = cur->parent;
-    } while (cur);
-    return FNValue::encodeUndefined();
+    return getByName(key.getString()->str);
   } else {
     auto &arr = static_cast<FNArray *>(this)->arr;
     double n = key.getNumber();
@@ -31,9 +39,9 @@ FNValue FNObject::getByVal(FNValue key) {
 }
 
 void FNObject::putByVal(FNValue key, FNValue val) {
-  if (key.isString())
-    props[key.getString()->str] = val;
-  else {
+  if (key.isString()) {
+    putByName(key.getString()->str, val);
+  } else {
     auto &arr = static_cast<FNArray *>(this)->arr;
     double n = key.getNumber();
     if (arr.size() <= n)

unsupported/juno/crates/flow_native/runtime/FNRuntime.h

@@ -159,6 +159,8 @@ struct FNObject {
   std::unordered_map<std::string, FNValue> props;
   FNObject *parent{};
 
+  FNValue getByName(const std::string &key);
+  void putByName(const std::string &key, FNValue val);
   FNValue getByVal(FNValue key);
   void putByVal(FNValue key, FNValue val);