LifetimePolicy.h

// Copyright(c) 2019 - 2020, #Momo
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// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met :
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// 1. Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
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// this software without specific prior written permission.
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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#pragma once

// Andrei's Alexandrescu SingletonHolder (see "Modern C++ Design" ch. 6)

namespace MxEngine
{
    using AtExitFunctionPointer = void (*)();

    template <class T>
    class DefaultLifetime
    {
    public:
        static inline void ScheduleDestruction(T*, AtExitFunctionPointer func)
        {
            std::atexit(func);
        }

        static inline void OnDeadReference() { }
    };

    template <class T>
    class NoDestroy
    {
    public:
        static inline void ScheduleDestruction(T*, AtExitFunctionPointer) { }

        static inline void OnDeadReference() { }
    };

    template <class T>
    class PhoenixSingleton
    {
    public:
        static inline void ScheduleDestruction(T*, AtExitFunctionPointer func)
        {
            if (!destroyedOnce)
                std::atexit(func);
        }

        static inline void OnDeadReference()
        {
            destroyedOnce = true;
        }

    private:
        inline static bool destroyedOnce = false;
    };
}