From 3770d4df45b37720e318669496c006fb6e72a3d7 Mon Sep 17 00:00:00 2001
From: Valentin Shergin <shergin@fb.com>
Date: Sat, 4 Aug 2018 09:30:32 -0700
Subject: [PATCH] Fabric: Using `const &` type for `ShadowNodeFragment`'s
 fields

Summary:
@public
To avoid unnecessary copying of `shared_ptr`s inside ShadowNodeFragment, now we store them as `const &` references.

Reviewed By: mdvacca

Differential Revision: D8988388

fbshipit-source-id: 0b3582e57ce7577b8fa819392bf33f34e1a60b59
---
 .../components/view/ConcreteViewShadowNode.h  |  1 +
 .../ConcreteComponentDescriptor.h             |  2 +
 .../fabric/core/shadownode/ShadowNode.cpp     |  1 +
 .../fabric/core/shadownode/ShadowNode.h       | 11 +----
 .../core/shadownode/ShadowNodeFragment.cpp    | 34 +++++++++++++++
 .../core/shadownode/ShadowNodeFragment.h      | 42 +++++++++++++++++++
 .../fabric/uimanager/FabricUIManager.cpp      |  1 +
 7 files changed, 83 insertions(+), 9 deletions(-)
 create mode 100644 ReactCommon/fabric/core/shadownode/ShadowNodeFragment.cpp
 create mode 100644 ReactCommon/fabric/core/shadownode/ShadowNodeFragment.h

diff --git a/ReactCommon/fabric/components/view/ConcreteViewShadowNode.h b/ReactCommon/fabric/components/view/ConcreteViewShadowNode.h
index fb1228b75..209a85940 100644
--- a/ReactCommon/fabric/components/view/ConcreteViewShadowNode.h
+++ b/ReactCommon/fabric/components/view/ConcreteViewShadowNode.h
@@ -14,6 +14,7 @@
 #include <fabric/core/ConcreteShadowNode.h>
 #include <fabric/core/LayoutableShadowNode.h>
 #include <fabric/core/ShadowNode.h>
+#include <fabric/core/ShadowNodeFragment.h>
 #include <fabric/debug/DebugStringConvertibleItem.h>
 
 namespace facebook {
diff --git a/ReactCommon/fabric/core/componentdescriptor/ConcreteComponentDescriptor.h b/ReactCommon/fabric/core/componentdescriptor/ConcreteComponentDescriptor.h
index 31a0fb623..0ec1cba19 100644
--- a/ReactCommon/fabric/core/componentdescriptor/ConcreteComponentDescriptor.h
+++ b/ReactCommon/fabric/core/componentdescriptor/ConcreteComponentDescriptor.h
@@ -13,6 +13,8 @@
 #include <fabric/core/ComponentDescriptor.h>
 #include <fabric/core/Props.h>
 #include <fabric/core/ShadowNode.h>
+#include <fabric/core/ShadowNodeFragment.h>
+#include <fabric/events/EventDispatcher.h>
 
 namespace facebook {
 namespace react {
diff --git a/ReactCommon/fabric/core/shadownode/ShadowNode.cpp b/ReactCommon/fabric/core/shadownode/ShadowNode.cpp
index 9fdb725af..2fc759237 100644
--- a/ReactCommon/fabric/core/shadownode/ShadowNode.cpp
+++ b/ReactCommon/fabric/core/shadownode/ShadowNode.cpp
@@ -9,6 +9,7 @@
 
 #include <string>
 
+#include <fabric/core/ShadowNodeFragment.h>
 #include <fabric/debug/DebugStringConvertible.h>
 #include <fabric/debug/debugStringConvertibleUtils.h>
 
diff --git a/ReactCommon/fabric/core/shadownode/ShadowNode.h b/ReactCommon/fabric/core/shadownode/ShadowNode.h
index 762f1ef7e..dca542b3f 100644
--- a/ReactCommon/fabric/core/shadownode/ShadowNode.h
+++ b/ReactCommon/fabric/core/shadownode/ShadowNode.h
@@ -21,6 +21,8 @@
 namespace facebook {
 namespace react {
 
+struct ShadowNodeFragment;
+
 class ShadowNode;
 
 using SharedShadowNode = std::shared_ptr<const ShadowNode>;
@@ -29,15 +31,6 @@ using SharedShadowNodeList = std::vector<std::shared_ptr<const ShadowNode>>;
 using SharedShadowNodeSharedList = std::shared_ptr<const SharedShadowNodeList>;
 using SharedShadowNodeUnsharedList = std::shared_ptr<SharedShadowNodeList>;
 
-struct ShadowNodeFragment {
-  Tag tag;
-  Tag rootTag;
-  SharedProps props;
-  SharedEventEmitter eventEmitter;
-  SharedShadowNodeSharedList children;
-  SharedLocalData localData;
-};
-
 using ShadowNodeCloneFunction = std::function<UnsharedShadowNode(
   const SharedShadowNode &sourceShadowNode,
   const ShadowNodeFragment &fragment
diff --git a/ReactCommon/fabric/core/shadownode/ShadowNodeFragment.cpp b/ReactCommon/fabric/core/shadownode/ShadowNodeFragment.cpp
new file mode 100644
index 000000000..7ec1f8bfb
--- /dev/null
+++ b/ReactCommon/fabric/core/shadownode/ShadowNodeFragment.cpp
@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include "ShadowNodeFragment.h"
+
+namespace facebook {
+namespace react {
+
+SharedProps &ShadowNodeFragment::nullSharedProps() {
+  static auto &instance = *new SharedProps();
+  return instance;
+}
+
+SharedEventEmitter &ShadowNodeFragment::nullSharedEventEmitter() {
+  static auto &instance = *new SharedEventEmitter();
+  return instance;
+}
+
+SharedShadowNodeSharedList &ShadowNodeFragment::nullSharedChildren() {
+  static auto &instance = *new SharedShadowNodeSharedList();
+  return instance;
+}
+
+SharedLocalData &ShadowNodeFragment::nullLocalData() {
+  static auto &instance = *new SharedLocalData();
+  return instance;
+}
+
+} // namespace react
+} // namespace facebook
diff --git a/ReactCommon/fabric/core/shadownode/ShadowNodeFragment.h b/ReactCommon/fabric/core/shadownode/ShadowNodeFragment.h
new file mode 100644
index 000000000..aa7314de5
--- /dev/null
+++ b/ReactCommon/fabric/core/shadownode/ShadowNodeFragment.h
@@ -0,0 +1,42 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <fabric/core/LocalData.h>
+#include <fabric/core/Props.h>
+#include <fabric/core/ReactPrimitives.h>
+#include <fabric/core/ShadowNode.h>
+#include <fabric/events/EventEmitter.h>
+
+namespace facebook {
+namespace react {
+
+/*
+ * An object which supposed to be used as a parameter specifying a shape
+ * of created or cloned ShadowNode.
+ * Note: Most of the fields are `const &` references (essentially just raw
+ * pointers) which means that the Fragment does not copy/store them or
+ * retain ownership of them.
+ */
+struct ShadowNodeFragment {
+  Tag tag = 0;
+  Tag rootTag = 0;
+  const SharedProps &props = nullSharedProps();
+  const SharedEventEmitter &eventEmitter = nullSharedEventEmitter();
+  const SharedShadowNodeSharedList &children = nullSharedChildren();
+  const SharedLocalData &localData = nullLocalData();
+
+private:
+  static SharedProps &nullSharedProps();
+  static SharedEventEmitter &nullSharedEventEmitter();
+  static SharedShadowNodeSharedList &nullSharedChildren();
+  static SharedLocalData &nullLocalData();
+};
+
+} // namespace react
+} // namespace facebook
diff --git a/ReactCommon/fabric/uimanager/FabricUIManager.cpp b/ReactCommon/fabric/uimanager/FabricUIManager.cpp
index 1ecd1b25b..11f6b362d 100644
--- a/ReactCommon/fabric/uimanager/FabricUIManager.cpp
+++ b/ReactCommon/fabric/uimanager/FabricUIManager.cpp
@@ -14,6 +14,7 @@
 #include <fabric/components/view/ViewShadowNode.h>
 #include <fabric/core/componentDescriptor.h>
 #include <fabric/core/LayoutContext.h>
+#include <fabric/core/ShadowNodeFragment.h>
 #include <fabric/debug/DebugStringConvertible.h>
 #include <fabric/debug/DebugStringConvertibleItem.h>