代码环境为VScode + CMake + GCC 8.1.0
首先，如何才能做到给我一个名字我就能拿到这个对象的这个值，也是比较难的一个地方，方法如下
#define OFFSET(className,fieldName) (size_t)&(((className*)0)->fieldName)
这个能够得到该成员变量与该对象的偏移量，之后根据这个偏移量来获取成员的值
正题开始
首先这个反射类应该只有一个，要不然反射就会变得很混乱，这一个反射对象，那里一个反射对象。所以应该将该反射类变为一个单例。全局内只允许出现一个。单例类如下：
Singleton.h
#pragma once
#include "Singleton.h"
#ifndef _SINGLETON_
#define _SINGLETON_
#include "Util.h"
NAME_SPACE_START(myUtil)
//单例模式
template<typename T>
class Singleton{
public:
static T* Instance(){
if(m_instance==nullptr){
m_instance = new T();
}
return m_instance;
}
private:
Singleton();
Singleton(const Singleton<T>&);
~Singleton();
Singleton<T>& operator=(const Singleton<T>&);
private:
static T* m_instance;
};
template<typename T>
T* Singleton<T>::m_instance=nullptr;
#define SINGLETON_DECLARE(className) \
friend class Singleton<className>; \
className(){
}; \
className(const className&){
}; \
~className(){
}; \
className& operator=(const className&);
NAME_SPACE_END()
#endif //!_SINGLETON_
我在这个头文件中写了一个单例声明SINGLETON_DECLARE，只要将这个声明放到私有部分就行了，这个类就变为一个单例类了。
反射类
如何才能做到反射呢，应该在这个反射类中保存注册表，传入了对应的类名，返回对应的信息，然后使用基类实现对应的方法即可。代码如下：
Reflex.h
#pragma once
#include "Util.h"
#include <cstdint>
#include <vadefs.h>
#include <vector>
#include <functional>
#ifndef _REFLEX_
#define _REFLEX_
NAME_SPACE_START(myUtil)
#include "Singleton.h"
#include <map>
#include <string>
//因为编译器不支持类模板和实现分开写，所以放到一起了
class Field;
class Reflex;
class RObject{
public:
RObject(){
}
virtual ~RObject(){
}
std::string _className;
template<typename T>
T get(const std::string& fieldName);
template<typename T>
void set(const std::string& fieldName, const T& fieldValue);
void Call(const std::string& methodName);
template<typename T,typename... Args>
T Call(const std::string& methodName, Args... args);
};
typedef RObject* (*construct)(void);
//使用方法,使用REGISTER_REFLEX注册，然后直接使用createClass即可
class Reflex{
SINGLETON_DECLARE(Reflex)
public:
void ReflexRegister();
RObject* createClass(const std::string& className);
void RegisterClass(const std::string& className, construct constructMethod);
void RegisterField(const std::string& className, const std::string& FieldName, const std::string& FieldType, const size_t& offset);
void RegisterMethod(const std::string& className, const std::string& methodName, const uintptr_t& lpMethod);
template<typename T>
T getClassField(void* originPos, const std::string& className, const std::string& fieldName);
template<typename T>
void setClassField(void* originPos, const std::string& className, const std::string& fieldName, const T& fieldValue);
uintptr_t getClassMethod(const std::string& className, const std::string& methodName);
private:
std::map<std::string, construct> m_classMap;
std::map<std::string, std::map<std::string, Field>> m_fieldMap;
std::map<std::string, std::map<std::string, uintptr_t>> m_methodMap;
};
//仅仅用来在reflex中注册使用
class RegisterClass{
public:
RegisterClass(const std::string& className,construct constructMethod)
{
Reflex* factory = myUtil::Singleton<Reflex>::Instance();
factory->RegisterClass(className, constructMethod);
}
RegisterClass(const std::string& className,const std::string& fieldName,const std::string& fieldType,const size_t& offset)
{
Reflex* factory = myUtil::Singleton<Reflex>::Instance();
factory->RegisterField(className, fieldName, fieldType, offset);
}
RegisterClass(const std::string& className,const std::string& methodName,const uintptr_t& lpMethod)
{
Reflex* factory = myUtil::Singleton<Reflex>::Instance();
factory->RegisterMethod(className, methodName, lpMethod);
}
};
class Field{
private:
std::string m_fieldType{
""};
//std::string m_fieldName{""};
size_t m_offset{
0};
public:
Field(){
}
Field(const std::string& fieldType,const size_t& offset):
m_fieldType(fieldType),m_offset(offset){
}
~Field(){
}
inline std::string getFieldType(){
return m_fieldType;}
//inline std::string getFieldName(){return m_fieldName;}
inline size_t getOffSet(){
return m_offset;}
inline void setFieldType(const std::string& type){
m_fieldType = type;}
//inline void setFieldName(const std::string& name){ m_fieldName = name;}
inline void setOffSet(const size_t& offset){
m_offset = offset;}
};
class Method{
public:
Method(){
}
Method(const std::string& name,const std::uintptr_t& method):
methodName(name),lpMethod(method){
}
~Method(){
}
inline void setMethodName(const std::string& name) {
methodName = name;}
inline void setLpMethod(const uintptr_t& lp) {
lpMethod = lp;}
inline std::string getMethodName(){
return methodName;}
inline uintptr_t getLpMethod(){
return lpMethod;}
private:
std::string methodName{
""};
std::uintptr_t lpMethod{
0};
};
#define REGISTER_REFLEX(className) \
RObject* construct##className() \
{
\
RObject* obj = new className(); \
obj->_className = #className; \
return obj; \
} \
RegisterClass registerClass##className(#className,construct##className);
#define REGISTER_REFLEX_FIELD(className,fieldType,fieldName) \
RegisterClass registerClass##className##fieldType##fieldName(#className,#fieldName,#fieldType,OFFSET(className,fieldName));
#define REGISTER_REFLEX_METHOD(className,methodName) \
std::function<void(className)> className##methodName = &className::methodName;\
RegisterClass registerClass##className##method(#className,#methodName,(std::uintptr_t)&className##methodName);
#define REGISTER_REFLEX_METHOD_ARGS(className,methodName,returnType,...) \
std::function<returnType(className,##__VA_ARGS__)> className##methodName = &className::methodName;\
RegisterClass registerClass##className##method##returnType(#className,#methodName,(std::uintptr_t)&className##methodName);
template<typename T>
T RObject::get(const std::string &fieldName)
{
Reflex* factory = myUtil::Singleton<Reflex>::Instance();
return factory->getClassField<T>(this, _className, fieldName);
}
template<typename T>
void RObject::set(const std::string &fieldName, const T &fieldValue)
{
Reflex* factory = myUtil::Singleton<Reflex>::Instance();
factory->setClassField(this, _className, fieldName, fieldValue);
}
void RObject::Call(const std::string& methodName)
{
Reflex* factory = myUtil::Singleton<Reflex>::Instance();
std::uintptr_t temp = factory->getClassMethod(_className, methodName);
if (temp == 0) return;
typedef std::function<void(decltype(this))> class_method;
class_method* method = (class_method*)temp;
(*method)(this);
}
template<typename T,typename... Args>
T RObject::Call(const std::string& methodName,Args... args)
{
Reflex* factory = myUtil::Singleton<Reflex>::Instance();
std::uintptr_t temp = factory->getClassMethod(_className, methodName);
if(temp == 0) return T();
typedef std::function<T(decltype(this),Args...)> class_method;
class_method* method = (class_method*)temp;
return (*method)(this,args...);
}
RObject* Reflex::createClass(const std::string &className)
{
if(m_classMap.find(className)==m_classMap.end()) return nullptr;
return m_classMap[className]();
}
void Reflex::RegisterClass(const std::string &className, construct constructMethod)
{
if(m_classMap.find(className)!=m_classMap.end()){
throw std::exception();
return;
}
m_classMap.insert(std::pair<std::string, construct>(className,constructMethod));
m_fieldMap[className] = std::map<std::string, Field>();
m_methodMap[className] = std::map<std::string, uintptr_t>();
}
void Reflex::RegisterField(const std::string &className, const std::string &FieldName, const std::string &FieldType, const size_t &offset)
{
m_fieldMap[className][FieldName] = Field(FieldType,offset);
}
void Reflex::RegisterMethod(const std::string &className, const std::string &methodName, const uintptr_t &lpMethod)
{
m_methodMap[className][methodName] = lpMethod;
}
template<typename T>
T Reflex::getClassField(void* originPos, const std::string &className, const std::string &fieldName)
{
if(m_fieldMap.find(className) == m_fieldMap.end()){
return T();
}
if(m_fieldMap[className].find(fieldName) == m_fieldMap[className].end()){
return T();
}
size_t offset = m_fieldMap[className][fieldName].getOffSet();
return *(T*)((size_t)originPos + offset);
}
template<typename T>
void Reflex::setClassField(void* originPos, const std::string &className, const std::string &fieldName, const T &fieldValue)
{
if(m_fieldMap.find(className) == m_fieldMap.end()){
return;
}
if(m_fieldMap[className].find(fieldName) == m_fieldMap[className].end()){
return;
}
size_t offset = m_fieldMap[className][fieldName].getOffSet();
*(T*)((size_t)originPos + offset) = fieldValue;
}
uintptr_t Reflex::getClassMethod(const std::string &className, const std::string &methodName)
{
if(m_fieldMap.find(className) == m_fieldMap.end()){
return 0;
}
if(m_methodMap[className].find(methodName) == m_methodMap[className].end()){
return 0;
}
return m_methodMap[className][methodName];
}
NAME_SPACE_END()
#endif //!_REFLEX_
该反射类使用方法如下：
#include <iostream>
#include <string>
#include "Util.h"
#include "Singleton.h"
#include "Reflex.h"
using namespace std;
using namespace myUtil;
class A:public RObject{
public:
void show(){
cout<<"hello world"<<endl;
}
int add(int a,int b){
return a+b;
}
int m_age;
A():m_age(10){
}
};
REGISTER_REFLEX(A)
REGISTER_REFLEX_FIELD(A, int, m_age)
REGISTER_REFLEX_METHOD(A, show)
REGISTER_REFLEX_METHOD_ARGS(A, add, int,int,int)
int main(){
Reflex* factory=Singleton<Reflex>::Instance();
A* a=(A*)factory->createClass("A");
cout<<a->get<int>("m_age")<<endl;
a->set<int>("m_age", 30);
cout << a->get<int>("m_age") << endl;
a->Call("show");
int b = a->Call<int,int,int>("add",1,5);
cout << b << endl;
A* c=(A*)factory->createClass("A");
cout<<c->get<int>("m_age")<<endl;
c->set<int>("m_age", 40);
cout << c->get<int>("m_age") << endl;
c->Call("show");
b = c->Call<int,int,int>("add",2,5);
cout << b << endl;
return 0;
}
结果截图
最后讲解一下是怎么用的，见注释
//首先要使用反射的类要继承RObject
//要使用反射的类和成员方法都要声明为public
class A:public RObject{
public:
void show(){
cout<<"hello world"<<endl;
}
int add(int a,int b){
return a+b;
}
int m_age;
A():m_age(10){
}
};
//这里在反射类中注册A这个类，原理是把重复工作用宏展开来替代
REGISTER_REFLEX(A)
//注册类中的成员变量，一定要先注册类再注册成员变量，原理是将成员变量与对象的偏移量保存起来，用到的时候解引用来获取值
REGISTER_REFLEX_FIELD(A, int, m_age)
//注册类的成员方法，此宏是声明没有返回值和入参的成员方法的，原理是使用function能够调用成员函数的功能，将function的地址保存到注册表中（转为uintptr_t），需要时通过传入的参数转换回来，再调用
REGISTER_REFLEX_METHOD(A, show)
//注册类的成员方法，此宏是声明有返回值和多参数的成员方法的，原理同上
REGISTER_REFLEX_METHOD_ARGS(A, add, int,int,int)
int main(){
//在使用类时，要先获取这个全局唯一的反射对象，使用它来创建对象
Reflex* factory=Singleton<Reflex>::Instance();
A* a=(A*)factory->createClass("A");
//为了能够得到准确的类型值，这里使用模板来获取
cout<<a->get<int>("m_age")<<endl;
//设置同获取
a->set<int>("m_age", 30);
cout << a->get<int>("m_age") << endl;
//调用无参且无返回值的成员函数时使用没有模板的Call，反之使用有模板的Call
a->Call("show");
int b = a->Call<int,int,int>("add",1,5);
cout << b << endl;
return 0;
}