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* Copyright 2019 Google LLC
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkReflected_DEFINED
#define SkReflected_DEFINED
#include "include/core/SkColor.h"
#include "include/core/SkRefCnt.h"
#include "include/private/SkTArray.h"
#include <functional> // std::function
#include <string.h>
class SkFieldVisitor;
struct SkPoint;
class SkString;
* Classes and macros for a lightweight reflection system.
* Classes that derive from SkReflected have several features:
* - Access to an SkReflected::Type instance, via static GetType() or virtual getType()
* The Type instance can be used to create additional instances (fFactory), get the name
* of the type, and answer queries of the form "is X derived from Y".
* - Given a string containing a type name, SkReflected can create an instance of that type.
* - SkReflected::VisitTypes can be used to enumerate all Types.
* Together, this simplifies the implementation of serialization and other dynamic type factories.
* Finally, all SkReflected-derived types must implement visitFields, which provides field-level
* reflection, in conjunction with SkFieldVisitor. See SkFieldVisitor, below.
* To create a new reflected class:
* - Derive the class (directly or indirectly) from SkReflected.
* - Ensure that the class can be default constructed.
* - In the public area of the class declaration, add REFLECTED(<ClassName>, <BaseClassName>).
* If the class is abstract, use REFLECTED_ABSTRACT(<ClassName>, <BaseClassName>) instead.
* - Add a one-time call to REGISTER_REFLECTED(<ClassName>) at initialization time.
* - Implement visitFields(), as described below.
class SkReflected : public SkRefCnt {
typedef sk_sp<SkReflected>(*Factory)();
struct Type {
const char* fName;
const Type* fBase;
Factory fFactory;
bool fRegistered = false;
bool isDerivedFrom(const Type* t) const {
const Type* base = fBase;
while (base) {
if (base == t) {
return true;
base = base->fBase;
return false;
virtual const Type* getType() const = 0;
static const Type* GetType() {
static Type gType{ "SkReflected", nullptr, nullptr };
return &gType;
bool isOfType(const Type* t) const {
const Type* thisType = this->getType();
return thisType == t || thisType->isDerivedFrom(t);
static sk_sp<SkReflected> CreateInstance(const char* name) {
for (const Type* type : gTypes) {
if (0 == strcmp(name, type->fName)) {
return type->fFactory();
return nullptr;
virtual void visitFields(SkFieldVisitor*) = 0;
static void VisitTypes(std::function<void(const Type*)> visitor);
static void RegisterOnce(Type* type) {
if (!type->fRegistered) {
type->fRegistered = true;
static SkSTArray<16, const Type*, true> gTypes;
static sk_sp<SkReflected> CreateProc() { \
return sk_sp<SkReflected>(new TYPE()); \
} \
static const Type* GetType() { \
static Type gType{ #TYPE, BASE::GetType(), CreateProc }; \
RegisterOnce(&gType); \
return &gType; \
} \
const Type* getType() const override { return GetType(); }
static const Type* GetType() { \
static Type gType{ #TYPE, BASE::GetType(), nullptr }; \
RegisterOnce(&gType); \
return &gType; \
} \
const Type* getType() const override { return GetType(); }
* SkFieldVisitor is an interface that can be implemented by any class to visit all fields of
* SkReflected types, and of types that implement the visitFields() function.
* Classes implementing the interface must supply implementations of virtual functions that visit
* basic types (float, int, bool, SkString), as well as helper methods for entering the scope of
* an object or array.
* All visit functions supply a field name, and a non-constant reference to an actual field.
* This allows visitors to serialize or deserialize collections of objects, or perform edits on
* existing objects.
* Classes that implement visitFields (typically derived from SkReflected) should simply call
* visit() for each of their fields, passing a (unique) field name, and the actual field. If your
* class has derived fields, it's best to only visit() the fields that you would serialize, then
* enforce any constraints afterwards.
* See SkParticleSerialization.h for example visitors that perform serialization to and from JSON.
class SkFieldVisitor {
virtual ~SkFieldVisitor() {}
// Visit functions for primitive types, to be implemented by derived visitors.
virtual void visit(const char*, float&) = 0;
virtual void visit(const char*, int&) = 0;
virtual void visit(const char*, bool&) = 0;
virtual void visit(const char*, SkString&) = 0;
// Specialization for SkTArrays. In conjunction with the enterArray/exitArray virtuals, this
// allows visitors to resize an array (for deserialization), and apply a single edit operation
// (remove a single element). Each element of the array is visited as normal.
template <typename T, bool MEM_MOVE>
void visit(const char* name, SkTArray<T, MEM_MOVE>& arr) {
arr.resize_back(this->enterArray(name, arr.count()));
for (int i = 0; i < arr.count(); ++i) {
this->visit(nullptr, arr[i]);
// Specialization for sk_sp pointers to types derived from SkReflected. Those types are known
// to implement visitFields. This allows the visitor to modify the contents of the object, or
// even replace it with an entirely new object. The virtual function uses SkReflected as a
// common type, but uses SkReflected::Type to communicate the required base-class. In this way,
// the new object can be verified to match the type of the original (templated) pointer.
template <typename T>
void visit(const char* name, sk_sp<T>& obj) {
sk_sp<SkReflected> newObj = obj;
this->visit(newObj, T::GetType());
if (newObj != obj) {
if (!newObj || newObj->isOfType(T::GetType())) {
} else {
if (obj) {
// Helper struct to allow exitArray to specify a single operation performed on the array.
struct ArrayEdit {
enum class Verb {
Verb fVerb = Verb::kNone;
int fIndex = 0;
template <typename T, bool MEM_MOVE>
void apply(SkTArray<T, MEM_MOVE>& arr) const {
switch (fVerb) {
case Verb::kNone:
case Verb::kRemove:
for (int i = fIndex; i < arr.count() - 1; ++i) {
arr[i] = arr[i + 1];
virtual void enterObject(const char* name) = 0;
virtual void exitObject() = 0;
virtual int enterArray(const char* name, int oldCount) = 0;
virtual ArrayEdit exitArray() = 0;
virtual void visit(sk_sp<SkReflected>&, const SkReflected::Type* baseType) = 0;
#endif // SkReflected_DEFINED