奇异递归模板模式

Curiously Recurring Template Pattern，CRTP

最近发现一个很优雅的写法，CRTP，利用了模版和继承的特性，实现了一种奇观的“自我认知”，可以省去写很多重复代码

C#实现一个单例

定义

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class Singleton<T> : MonoBehaviour where T : Component
{
    protected static T _instance;
    public static bool HasInstance => _instance != null;
    public static T Instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = FindObjectOfType<T> ();
                if (_instance == null)
                {
                    GameObject obj = new GameObject ();
                    obj.name = typeof(T).Name + "_AutoCreated";
                    _instance = obj.AddComponent<T> ();
                }
            }
            return _instance;
        }
    }
    protected virtual void Awake ()
    {
        InitializeSingleton();      
    }
    protected virtual void InitializeSingleton()
    {
        if (!Application.isPlaying)
        {
            return;
        }
        _instance = this as T;
    }
}

使用

public class GlobalTableManager : Singleton<GlobalTableManager>
{...}

C++实现一个单例

定义

#include <iostream>

template <typename T>
class Singleton {
protected:
    static T* instance;

    Singleton() {} // 构造函数私有，确保不能直接实例化

public:
    static T* getInstance() {
        if (!instance) {
            instance = new T();
        }
        return instance;
    }

    static void destroyInstance() {
        delete instance;
        instance = nullptr;
    }
};

template <typename T>
T* Singleton<T>::instance = nullptr;

使用

class MySingleton : public Singleton<MySingleton> {
public:
    void print()
    {
        std::cout << "Hello" << std::endl;
    }
};

int main() {
    MySingleton::getInstance()->print();
    return 0;
}