自動註冊工廠CSDN裏已經有人解析過了,這裏是學習過程中的總結、並詳細解析。話不多說,先看代碼:
oly_auto_factory.h
#pragma once
#include <functional>
#include <map>
#include <memory>
#include <string>
namespace oly {
/**
* T 需要傳入基類
*/
template <typename T>
class auto_factory {
public:
/**
* N 子類,這裏會把對應子類添加到Map中
*/
template <typename N>
struct register_t {
template <typename... Args>
register_t(const std::string& key, Args... args)
{
auto_factory::instance()->_map.emplace(key, [=] { return new N(args...); });
}
};
/**
* 普通指針
*/
static auto normal_ptr(const std::string& key) -> T*
{
return auto_factory::instance()->find(key);
}
/**
* unique_ptr指針
*/
static std::unique_ptr<T> unique_ptr(const std::string& key)
{
return std::unique_ptr<T>(normal_ptr(key));
}
/**
* shared_ptr指針
*/
static std::shared_ptr<T> shared_ptr(const std::string& key)
{
return std::shared_ptr<T>(normal_ptr(key));
}
private:
auto_factory(){};
auto_factory(const auto_factory&) = delete;
auto_factory(auto_factory&&) = delete;
auto_factory& operator=(const auto_factory&) = delete;
/**
* 單例模式
*/
static auto instance() -> auto_factory<T>*
{
static auto_factory<T> ins;
return &ins;
}
auto find(const std::string& key) -> T*
{
if (_map.find(key) == _map.end())
throw std::invalid_argument("key is not exist!");
return _map[key]();
}
std::map<std::string, std::function<T*()>> _map;
};
} // namespace oly
下面我們來看具體應用,基類class B
#include <iostream>
#include "oly_auto_factory.h"
class B {
public:
virtual void display() = 0;
};
/**
* 註冊基類
*/
#define AF_OBJECT oly::auto_factory<B>
/**
* 註冊子類,這裏沒有對繼承關係進行判斷,需要保證繼承關係
*/
#define REGISTER_AF_OBJECT_CLASS(CLASS, ...) AF_OBJECT::register_t<CLASS> __##CLASS(#CLASS, ##__VA_ARGS__)
子類 class FirstB; class SecondB ;class ThirdB
class FirstB : public B {
public:
void display() override
{
std::cout << __func__ << " FirstB\n";
}
};
REGISTER_AF_OBJECT_CLASS(FirstB);
class SecondB : public B {
public:
SecondB(const std::string name = "")
{
nameString = name;
}
void display() override
{
std::cout << __func__ << " SecondB\n";
std::cout << nameString << "\n";
}
private:
std::string nameString;
};
REGISTER_AF_OBJECT_CLASS(SecondB, "Welcome"); //帶參構造函數
class ThirdB : public B {
public:
ThirdB(int age, const std::string name = "")
{
nameString = name;
ageInt = age;
}
void display() override
{
std::cout << __func__ << " ThirdB\n";
std::cout << nameString << ":" << ageInt << "\n";
}
private:
std::string nameString;
int ageInt;
};
REGISTER_AF_OBJECT_CLASS(ThirdB, 20, "Tom"); //帶參構造函數
類下面的 REGISTER_AF_OBJECT_CLASS(FirstB); 是實現自動註冊的關鍵。當我看到這個REGISTER_AF_OBJECT_CLASS();時一臉懵逼,函數怎麼可以在函數體外執行???。
我們來分析一下,大家都知道應用#define 時替換原則,我們替換一下
REGISTER_AF_OBJECT_CLASS(FirstB); ==》 AF_OBJECT::register_t<FirstB> __FirstB('FirstB", ##__VA_ARGS__);
呵,這貨就是一個變量。而我們在變量的構造函數裏面把他放入std::map<std::string, std::function<T*()>> _map;Map中!
int main()
{
AF_OBJECT::normal_ptr("SecondB")->display();
AF_OBJECT::shared_ptr("ThirdB")->display();
return 0;
}