楼主
发表于：
2004-04-20 12:15:55
//File: class.h
#ifndef __CLASS_H__
#define __CLASS_H__
#include <string>
#include <map>
typedef void* (*FactoryMethod)(void);
class Registry;
/*
* 这个类是用来存储<name, create object function>对,
* 也就是个对象工厂.
*/
class Class
{
public:
static Class forName(std::string name)
{
return Class(name);
}
public:
void* newInstance(void)
{
std::map<std::string, FactoryMethod>::const_iterator find;
find = registry.find(name);
if (find == registry.end())
return NULL;
else
return (find->second)();
}
private:
friend class Registry;
static bool registerClass(std::string name, FactoryMethod method)
{
return registry.insert(std::make_pair(name, method)).second;
}
private:
static std::map<std::string, FactoryMethod> registry;
std::string name;
explicit Class(std::string n) : name(n)
{}
};
std::map<std::string, FactoryMethod> Class::registry;
class Registry
{
public:
Registry(const char* name, FactoryMethod method)
{
Class::registerClass(name, method);
}
};
/*
* mixed template, generate new instance for every class.
*/
template <class T, const char name[]>
class Registed
{
public:
static void* newInstance(void)
{
return new T();
}
protected:
Registed()
{
const Registry& dummy = r;
}
private:
static const Registry r;
};
/*
* static member, initiliazed before enter into main()
* call Class::registerClass by ctor of Registry
*/
template <class T, const char name[]> const Registry
Registed<T, name>::r = Registry(name, Registed<T, name>::newInstance);
#define REG_CLASS(CLASS) \
char NameArray[] = #CLASS; \
class CLASS : public Registed<CLASS, NameArray> \
#endif // __CLASS_H__
// Class.cc
#include <iostream>
#include "Class.h"
REG_CLASS(Test)
{
public:
Test() { std::cout << "Test" << std::endl; }
};
int main(int argc, char* argv[])
{
Class c = Class::forName("Test");
void* p = c.newInstance();
system("pause");
return 0;
}
编译环境: DEV C++, windows 2000 server.
运行结果: Test
让我奇怪的是模板类Registed中的protected构造器,
他到底起什么作用? 如果把这个构造器去掉,编译能够通过,
但运行没有结果,原因是Registed中的static member没有初始化,
从而Registry的构造器没有运行..
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