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hryhoriiK97meta-codesync[bot]
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Use a static cast for View nodes when building ShadowView layout metrics (#59290)
Summary: `ShadowView`'s constructor reads the node's layout metrics through `layoutMetricsFromShadowNode`, which uses `dynamic_cast<const LayoutableShadowNode *>` to find out whether the node has layout. The differ builds a `ShadowView` for every child it visits when it slices a node's children, so this runs for every visited node on every commit, including the per-frame commits that update a ScrollView's content offset. **Current behavior.** Every call pays for a `dynamic_cast`, which walks the type's inheritance information at runtime; for a `View`, the node's type is `ConcreteViewShadowNode<...>`, several levels below `LayoutableShadowNode`. In the profiles below, `__dynamic_cast` takes 19–21% of the differ's time while scrolling. **With this change.** A node with the `ViewKind` trait takes a `static_cast`. `ShadowNodeTraits` documents `ViewKind` as "Inherits `ConcreteViewShadowNode<>` template", and `ConcreteViewShadowNode::BaseTraits()` is the only place that sets it; `ConcreteViewShadowNode` derives from `YogaLayoutableShadowNode`, so such a node is always a `LayoutableShadowNode` and the result is the same as the `dynamic_cast`'s. Other nodes (for example raw text) keep the checked cast. Core code already relies on the trait the same way: `PointerEventsProcessor`, `YogaLayoutableShadowNode` and `LayoutAnimationKeyFrameManager` check `ViewKind` and then `static_cast` the props to `ViewProps`. ## Changelog: [GENERAL] [CHANGED] - Building a `ShadowView` for a View node no longer uses a `dynamic_cast` to read its layout metrics Pull Request resolved: #59290 Test Plan: - `clang-format --dry-run --Werror` on the changed file passes. - `yarn fantom` (full suite, with the tester rebuilt from this change): 188 test suites and 3,288 tests pass (108 skipped by their configuration). - RNTester built with `xcodebuild` in Release and run on a physical iPhone 15 Pro (iOS 26.6.1). - **Measurement.** The two arms are the same binary with the change switched by a launch argument, in the order before, after, after, before. Interactions were driven by [Argent](https://github.com/software-mansion/argent) on the physical iPhone, under Instruments' Time Profiler. Values are main-thread sampled time per launch inside `calculateShadowViewMutations` (the differ), averaged over the 2 launches of each arm. iPhone 15 Pro, Release: | RNTester screen, 10 flings (Playground chat: 40) | differ before | this PR | change | `__dynamic_cast` in the differ, before → this PR | |---|--:|--:|--:|--:| | Playground, chat of 500 messages | 338 ms | 280 ms | −17% | 64 → 14 ms | | FlatList basic | 187 ms | 150 ms | −20% | 38 → 0 ms | | SectionList scrollable | 296 ms | 290 ms | −2% | 63 → 10 ms | SectionList is mostly bound by the JS thread and renders a different amount in each launch, so its differ time varied from 237 to 356 ms between launches of the same arm; the time in `__dynamic_cast` is the stable number there. The differ is 7–9% of the main thread's time on these screens. Mounting 1000 views five times took 24–31 ms of differ time per launch in both arms, too little for the profiler's 1 ms samples to show a difference. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Reviewed By: christophpurrer Differential Revision: D126687891 Pulled By: javache fbshipit-source-id: 83440573d6fdb644843f3961a8e8ceade7875624
1 parent c1d8139 commit 79a5629

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Lines changed: 41 additions & 3 deletions

‎packages/react-native/ReactCommon/react/renderer/core/LayoutableShadowNode.h‎

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@@ -117,6 +117,11 @@ class LayoutableShadowNode : public ShadowNode {
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*/
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LayoutMetrics getLayoutMetrics() const;
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const LayoutableShadowNode *asLayoutable() const override
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{
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return this;
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}
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/*
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* Returns a transform object that represents transformations that will/should
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* be applied on top of regular layout metrics by mounting layer.
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#pragma mark - DebugStringConvertible
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#if RN_DEBUG_STRING_CONVERTIBLE
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SharedDebugStringConvertibleList getDebugProps() const;
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SharedDebugStringConvertibleList getDebugProps() const override;
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#endif
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LayoutMetrics layoutMetrics_;

‎packages/react-native/ReactCommon/react/renderer/core/ShadowNode.h‎

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@@ -27,6 +27,7 @@
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namespace facebook::react {
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class ComponentDescriptor;
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class LayoutableShadowNode;
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struct ShadowNodeFragment;
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struct ShadowNodeWrapper;
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@@ -122,6 +123,15 @@ class ShadowNode : public Sealable, public DebugStringConvertible, public jsi::N
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*/
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virtual void completeClone(const ShadowNode & /* sourceShadowNode */, const ShadowNodeFragment & /* fragment */) {}
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/**
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* Returns this node as a `LayoutableShadowNode`, or `nullptr` if it isn't
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* one. Cheaper than a `dynamic_cast`.
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*/
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virtual const LayoutableShadowNode *asLayoutable() const
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{
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return nullptr;
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}
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#pragma mark - Getters
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ComponentName getComponentName() const;

‎packages/react-native/ReactCommon/react/renderer/mounting/ShadowView.cpp‎

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@@ -13,8 +13,7 @@
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namespace facebook::react {
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static LayoutMetrics layoutMetricsFromShadowNode(const ShadowNode& shadowNode) {
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auto layoutableShadowNode =
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dynamic_cast<const LayoutableShadowNode*>(&shadowNode);
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auto layoutableShadowNode = shadowNode.asLayoutable();
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return layoutableShadowNode != nullptr
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? layoutableShadowNode->getLayoutMetrics()
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: EmptyLayoutMetrics;

‎scripts/cxx-api/api-snapshots/ReactAndroidDebugCxx.api‎

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@@ -1719,6 +1719,7 @@ class facebook::react::LayoutableShadowNode : public facebook::react::ShadowNode
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public virtual bool canBeTouchTarget() const;
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public virtual bool canChildrenBeTouchTarget() const;
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public virtual bool getIsLayoutClean() const = 0;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const override;
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public virtual facebook::react::Float baseline(const facebook::react::LayoutContext& layoutContext, facebook::react::Size size) const;
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public virtual facebook::react::Point getContentOriginOffset(bool includeTransform) const;
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public virtual facebook::react::Size measure(const facebook::react::LayoutContext& layoutContext, const facebook::react::LayoutConstraints& layoutConstraints) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneMultiple(const std::unordered_set<std::shared_ptr<const facebook::react::ShadowNodeFamily>>& familiesToUpdate, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode, const facebook::react::ShadowNodeFragment& fragment)>& callback) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneTree(const facebook::react::ShadowNodeFamily& shadowNodeFamily, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode)>& callback) const;
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public using AncestorList = std::vector<std::pair<std::reference_wrapper<const facebook::react::ShadowNode>, int>>;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const;
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public virtual void appendChild(const std::shared_ptr<const facebook::react::ShadowNode>& child);
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public virtual void completeClone(const facebook::react::ShadowNode&, const facebook::react::ShadowNodeFragment&);
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public virtual void replaceChild(const facebook::react::ShadowNode& oldChild, const std::shared_ptr<const facebook::react::ShadowNode>& newChild, size_t suggestedIndex = std::numeric_limits<size_t>::max());

‎scripts/cxx-api/api-snapshots/ReactAndroidFrameworksCxx.api‎

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@@ -2595,6 +2595,7 @@ class facebook::react::LayoutableShadowNode : public facebook::react::ShadowNode
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public virtual bool canBeTouchTarget() const;
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public virtual bool canChildrenBeTouchTarget() const;
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public virtual bool getIsLayoutClean() const = 0;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const override;
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public virtual facebook::react::Float baseline(const facebook::react::LayoutContext& layoutContext, facebook::react::Size size) const;
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public virtual facebook::react::Point getContentOriginOffset(bool includeTransform) const;
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public virtual facebook::react::Size measure(const facebook::react::LayoutContext& layoutContext, const facebook::react::LayoutConstraints& layoutConstraints) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneMultiple(const std::unordered_set<std::shared_ptr<const facebook::react::ShadowNodeFamily>>& familiesToUpdate, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode, const facebook::react::ShadowNodeFragment& fragment)>& callback) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneTree(const facebook::react::ShadowNodeFamily& shadowNodeFamily, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode)>& callback) const;
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public using AncestorList = std::vector<std::pair<std::reference_wrapper<const facebook::react::ShadowNode>, int>>;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const;
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public virtual void appendChild(const std::shared_ptr<const facebook::react::ShadowNode>& child);
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public virtual void completeClone(const facebook::react::ShadowNode&, const facebook::react::ShadowNodeFragment&);
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public virtual void replaceChild(const facebook::react::ShadowNode& oldChild, const std::shared_ptr<const facebook::react::ShadowNode>& newChild, size_t suggestedIndex = std::numeric_limits<size_t>::max());

‎scripts/cxx-api/api-snapshots/ReactAndroidNewarchCxx.api‎

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@@ -1718,6 +1718,7 @@ class facebook::react::LayoutableShadowNode : public facebook::react::ShadowNode
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public virtual bool canBeTouchTarget() const;
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public virtual bool canChildrenBeTouchTarget() const;
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public virtual bool getIsLayoutClean() const = 0;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const override;
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public virtual facebook::react::Float baseline(const facebook::react::LayoutContext& layoutContext, facebook::react::Size size) const;
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public virtual facebook::react::Point getContentOriginOffset(bool includeTransform) const;
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public virtual facebook::react::Size measure(const facebook::react::LayoutContext& layoutContext, const facebook::react::LayoutConstraints& layoutConstraints) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneMultiple(const std::unordered_set<std::shared_ptr<const facebook::react::ShadowNodeFamily>>& familiesToUpdate, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode, const facebook::react::ShadowNodeFragment& fragment)>& callback) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneTree(const facebook::react::ShadowNodeFamily& shadowNodeFamily, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode)>& callback) const;
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public using AncestorList = std::vector<std::pair<std::reference_wrapper<const facebook::react::ShadowNode>, int>>;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const;
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public virtual void appendChild(const std::shared_ptr<const facebook::react::ShadowNode>& child);
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public virtual void completeClone(const facebook::react::ShadowNode&, const facebook::react::ShadowNodeFragment&);
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public virtual void replaceChild(const facebook::react::ShadowNode& oldChild, const std::shared_ptr<const facebook::react::ShadowNode>& newChild, size_t suggestedIndex = std::numeric_limits<size_t>::max());

‎scripts/cxx-api/api-snapshots/ReactAndroidReleaseCxx.api‎

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@@ -1718,6 +1718,7 @@ class facebook::react::LayoutableShadowNode : public facebook::react::ShadowNode
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public virtual bool canBeTouchTarget() const;
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public virtual bool canChildrenBeTouchTarget() const;
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public virtual bool getIsLayoutClean() const = 0;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const override;
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public virtual facebook::react::Float baseline(const facebook::react::LayoutContext& layoutContext, facebook::react::Size size) const;
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public virtual facebook::react::Point getContentOriginOffset(bool includeTransform) const;
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public virtual facebook::react::Size measure(const facebook::react::LayoutContext& layoutContext, const facebook::react::LayoutConstraints& layoutConstraints) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneMultiple(const std::unordered_set<std::shared_ptr<const facebook::react::ShadowNodeFamily>>& familiesToUpdate, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode, const facebook::react::ShadowNodeFragment& fragment)>& callback) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneTree(const facebook::react::ShadowNodeFamily& shadowNodeFamily, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode)>& callback) const;
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public using AncestorList = std::vector<std::pair<std::reference_wrapper<const facebook::react::ShadowNode>, int>>;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const;
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public virtual void appendChild(const std::shared_ptr<const facebook::react::ShadowNode>& child);
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public virtual void completeClone(const facebook::react::ShadowNode&, const facebook::react::ShadowNodeFragment&);
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public virtual void replaceChild(const facebook::react::ShadowNode& oldChild, const std::shared_ptr<const facebook::react::ShadowNode>& newChild, size_t suggestedIndex = std::numeric_limits<size_t>::max());

‎scripts/cxx-api/api-snapshots/ReactAppleDebugCxx.api‎

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@@ -4002,6 +4002,7 @@ class facebook::react::LayoutableShadowNode : public facebook::react::ShadowNode
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public virtual bool canBeTouchTarget() const;
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public virtual bool canChildrenBeTouchTarget() const;
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public virtual bool getIsLayoutClean() const = 0;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const override;
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public virtual facebook::react::Float baseline(const facebook::react::LayoutContext& layoutContext, facebook::react::Size size) const;
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public virtual facebook::react::Point getContentOriginOffset(bool includeTransform) const;
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public virtual facebook::react::Size measure(const facebook::react::LayoutContext& layoutContext, const facebook::react::LayoutConstraints& layoutConstraints) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneMultiple(const std::unordered_set<std::shared_ptr<const facebook::react::ShadowNodeFamily>>& familiesToUpdate, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode, const facebook::react::ShadowNodeFragment& fragment)>& callback) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneTree(const facebook::react::ShadowNodeFamily& shadowNodeFamily, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode)>& callback) const;
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public using AncestorList = std::vector<std::pair<std::reference_wrapper<const facebook::react::ShadowNode>, int>>;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const;
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public virtual void appendChild(const std::shared_ptr<const facebook::react::ShadowNode>& child);
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public virtual void completeClone(const facebook::react::ShadowNode&, const facebook::react::ShadowNodeFragment&);
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public virtual void replaceChild(const facebook::react::ShadowNode& oldChild, const std::shared_ptr<const facebook::react::ShadowNode>& newChild, size_t suggestedIndex = std::numeric_limits<size_t>::max());

‎scripts/cxx-api/api-snapshots/ReactAppleFrameworksCxx.api‎

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@@ -4811,6 +4811,7 @@ class facebook::react::LayoutableShadowNode : public facebook::react::ShadowNode
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public virtual bool canBeTouchTarget() const;
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public virtual bool canChildrenBeTouchTarget() const;
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public virtual bool getIsLayoutClean() const = 0;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const override;
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public virtual facebook::react::Float baseline(const facebook::react::LayoutContext& layoutContext, facebook::react::Size size) const;
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public virtual facebook::react::Point getContentOriginOffset(bool includeTransform) const;
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public virtual facebook::react::Size measure(const facebook::react::LayoutContext& layoutContext, const facebook::react::LayoutConstraints& layoutConstraints) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneMultiple(const std::unordered_set<std::shared_ptr<const facebook::react::ShadowNodeFamily>>& familiesToUpdate, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode, const facebook::react::ShadowNodeFragment& fragment)>& callback) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneTree(const facebook::react::ShadowNodeFamily& shadowNodeFamily, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode)>& callback) const;
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public using AncestorList = std::vector<std::pair<std::reference_wrapper<const facebook::react::ShadowNode>, int>>;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const;
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public virtual void appendChild(const std::shared_ptr<const facebook::react::ShadowNode>& child);
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public virtual void completeClone(const facebook::react::ShadowNode&, const facebook::react::ShadowNodeFragment&);
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public virtual void replaceChild(const facebook::react::ShadowNode& oldChild, const std::shared_ptr<const facebook::react::ShadowNode>& newChild, size_t suggestedIndex = std::numeric_limits<size_t>::max());

‎scripts/cxx-api/api-snapshots/ReactAppleNewarchCxx.api‎

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@@ -3993,6 +3993,7 @@ class facebook::react::LayoutableShadowNode : public facebook::react::ShadowNode
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public virtual bool canBeTouchTarget() const;
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public virtual bool canChildrenBeTouchTarget() const;
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public virtual bool getIsLayoutClean() const = 0;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const override;
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public virtual facebook::react::Float baseline(const facebook::react::LayoutContext& layoutContext, facebook::react::Size size) const;
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public virtual facebook::react::Point getContentOriginOffset(bool includeTransform) const;
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public virtual facebook::react::Size measure(const facebook::react::LayoutContext& layoutContext, const facebook::react::LayoutConstraints& layoutConstraints) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneMultiple(const std::unordered_set<std::shared_ptr<const facebook::react::ShadowNodeFamily>>& familiesToUpdate, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode, const facebook::react::ShadowNodeFragment& fragment)>& callback) const;
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public std::shared_ptr<facebook::react::ShadowNode> cloneTree(const facebook::react::ShadowNodeFamily& shadowNodeFamily, const std::function<std::shared_ptr<facebook::react::ShadowNode>(const facebook::react::ShadowNode& oldShadowNode)>& callback) const;
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public using AncestorList = std::vector<std::pair<std::reference_wrapper<const facebook::react::ShadowNode>, int>>;
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public virtual const facebook::react::LayoutableShadowNode* asLayoutable() const;
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public virtual void appendChild(const std::shared_ptr<const facebook::react::ShadowNode>& child);
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public virtual void completeClone(const facebook::react::ShadowNode&, const facebook::react::ShadowNodeFragment&);
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public virtual void replaceChild(const facebook::react::ShadowNode& oldChild, const std::shared_ptr<const facebook::react::ShadowNode>& newChild, size_t suggestedIndex = std::numeric_limits<size_t>::max());

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