ManagedInstance.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "pma/PolyAllocator.h"
 
#ifdef _MSC_VER
    #pragma warning(push)
    #pragma warning(disable : 4365 4987)
#endif
#include <functional>
#include <memory>
#include <utility>
#ifdef _MSC_VER
    #pragma warning(pop)
#endif
 
namespace pma {
 
class MemoryResource;
 
namespace impl {
 
template<class TPointer, class TTarget, class TBase = TTarget>
class ManagedInstance {
    public:
        using PointerType = TPointer;
 
    private:
        explicit ManagedInstance(MemoryResource* memRes) : pMemRes{memRes} {
        }
 
    public:
        static ManagedInstance with(MemoryResource* memRes) {
            return ManagedInstance{memRes};
        }
 
        template<typename ... Args>
        PointerType create(Args&& ... args) {
            pma::PolyAllocator<TTarget> alloc{pMemRes};
            auto deleter = [alloc](TBase* ptr) mutable {
                    alloc.deleteObject(static_cast<TTarget*>(ptr));
                };
            return {alloc.newObject(std::forward<Args>(args)...), deleter};
        }
 
    private:
        MemoryResource* pMemRes;
 
};
 
}  // namespace impl
 
template<class TTarget, class TBase = TTarget>
using UniqueInstance = impl::ManagedInstance<std::unique_ptr<TBase, std::function<void (TBase*)> >, TTarget, TBase>;
 
template<class TTarget, class TBase = TTarget>
using SharedInstance = impl::ManagedInstance<std::shared_ptr<TBase>, TTarget, TBase>;
 
}  // namespace pma