ObjectPool.h

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// Copyright Blue Isle Studios Inc 2021. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "ObjectPool.generated.h"
 
#define DEBUG_OBJECT_POOL 0
 
UCLASS()
class PROJECTX_API AObjectPool : public AActor
{
    GENERATED_BODY()
    
public: 
    AObjectPool();
 
    static TMap<TWeakObjectPtr<UWorld>, AObjectPool*> Singleton;
    TMap<TSubclassOf<AActor>, TArray<AActor*>> ObjectPool;
 
    static AObjectPool* Get(UObject* const WorldContextObject);
    virtual void EndPlay(const EEndPlayReason::Type EndPlayReason) override;
 
    template< class T >
    T* SpawnActorDeferred(
        UClass* Class,
        FTransform const& Transform,
        AActor* Owner = nullptr,
        AActor* Instigator = nullptr
    )
    {
        UWorld* const World = GetWorld();
        if (!World || World->bIsTearingDown)
        {
            return nullptr;
        }
 
        if (!ObjectPool.Contains(Class))
        {
            ObjectPool.Add(Class);
        }
 
        TArray<AActor*>& AvailablePool = ObjectPool[Class];
        for (int i = AvailablePool.Num()-1; i >= 0; i--)
        {
            AActor* const SpawnedActor = AvailablePool[i];
            AvailablePool.RemoveAt(i);
 
            if (!SpawnedActor || SpawnedActor->IsPendingKillPending())
            {
                continue;
            }
 
            SpawnedActor->SetOwner(Owner);
            SpawnedActor->SetInstigator(Instigator);
            SpawnedActor->SetActorTransform(Transform);
 
            #if DEBUG_OBJECT_POOL
            UE_LOG(LogTemp, Log, TEXT("[Object Pool] Reuse Actor '%s' from pool. Available of type: %d"), *SpawnedActor->GetName(), AvailablePool.Num());
            #endif
 
            return Cast<T>(SpawnedActor);
        }
        #if DEBUG_OBJECT_POOL
            UE_LOG(LogTemp, Log, TEXT("[Object Pool] Spawned Actor '%s'. No pool actors available. Will cache to pool."), *Class->GetName());
        #endif
        return World->SpawnActorDeferred<T>(Class, Transform, Owner, Instigator, ESpawnActorCollisionHandlingMethod::AlwaysSpawn);
    }
 
    void FinishSpawning(AActor* const Actor, FTransform const& Transform);
    void ReleaseActorToPool(AActor* const Actor);
};