// ObjectPool.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

#include "pch.h"
#include <iostream>
#include <string>
#include <functional>
#include <memory>
#include <map>

using namespace std;
const int MaxObjectNum = 10;

class NonCopyable
{
protected:
	NonCopyable() = default;
	~NonCopyable() = default;
	// 禁用复制构造
	NonCopyable(const NonCopyable&) = delete;
	// 禁用赋值构造
	NonCopyable& operator = (const NonCopyable&) = delete;
};

template<typename T>
class ObjectPool :NonCopyable
{
	template<typename...Args>
	using Constructor = function<shared_ptr<T>(Args...)>;
public:
	// 默认创建多少个对象
	template<typename... Args>
	void Init(size_t num, Args&&...args)
	{
		if (num <=0 || num>MaxObjectNum)
		{
			throw logic_error("object num out of range.");
		}
		// 不区分引用
		auto constructName = typeid(Constructor<Args...>).name();
		for (size_t i =0;i<num;i++)
		{
			m_object_map.emplace(constructName, shared_ptr<T>(new T(forward<Args>(args)...), [this, constructName](T*p) {
				//删除器中不直接删除对象，而是回收到对象池中，以供下次使用
				m_object_map.emplace(move(constructName), shared_ptr<T>(p));
			}));

		}
	}
	// 从对象池中获取一个对象
	template<typename... Args>
	shared_ptr<T> Get()
	{
		string constructName = typeid(Constructor<Args...>).name();
		auto range = m_object_map.equal_range(constructName);
		for (auto it = range.first; it != range.second;++it)
		{
			auto ptr = it->second;
			m_object_map.erase(it);
			return ptr;
		}
		return nullptr;
	}
private:
	multimap<string,shared_ptr<T>> m_object_map;
};

struct BigObject
{
	BigObject() {}
	BigObject(int a) {}

	BigObject(const int& a, const int&b) {}
	void Print(const string& str)
	{
		cout << str << endl;
	}
};

void Print(shared_ptr<BigObject>p, const string& str)
{
	if (p != nullptr)
	{
		p->Print(str);
	}
}

void TestObjPool()
{
	ObjectPool<BigObject> pool;
	pool.Init(2);
	{
		auto p = pool.Get();
		Print(p, "p");
		auto p2 = pool.Get();
		Print(p2, "p2");
		// 出了作用哉之后，对象池返回出来的对象又会自动回收
	}
	auto p = pool.Get();
	Print(p, "p");
	auto p2 = pool.Get();
	Print(p2, "p2");

	// 对象池支持重载构造函数
	pool.Init(2, 1);
	auto p4 = pool.Get<int>();
	Print(p4, "p4");
	pool.Init(2, 1, 2);
	auto p5 = pool.Get<int, int>();
	Print(p5, "p5");
}
int main()
{
	TestObjPool();
}

结果显示: