com.unity.perception/com.unity.perception/Runtime/Randomization/Randomizers/RandomizerExamples/Utilities/GameObjectOneWayCache.cs

using System;
using System.Collections.Generic;
using Unity.Profiling;
using UnityEngine;

namespace UnityEngine.Perception.Randomization.Randomizers.Utilities
{
    /// <summary>
    /// Facilitates object pooling for a pre-specified collection of prefabs with the caveat that objects can be fetched
    /// from the cache but not returned. Every frame, the cache needs to be reset, which will return all objects to the pool
    /// </summary>
    class GameObjectOneWayCache
    {
        static ProfilerMarker s_ResetAllObjectsMarker = new ProfilerMarker("ResetAllObjects");

        // Objects will reset to this origin when not being used
        Transform m_CacheParent;
        Dictionary<int, int> m_InstanceIdToIndex;
        List<GameObject>[] m_InstantiatedObjects;
        int[] m_NumObjectsActive;
        int NumObjectsInCache { get; set; }
        public int NumObjectsActive { get; private set; }

        public GameObjectOneWayCache(Transform parent, GameObject[] prefabs)
        {
            m_CacheParent = parent;
            m_InstanceIdToIndex = new Dictionary<int, int>();
            m_InstantiatedObjects = new List<GameObject>[prefabs.Length];
            m_NumObjectsActive = new int[prefabs.Length];

            var index = 0;
            foreach (var prefab in prefabs)
            {
                var instanceId = prefab.GetInstanceID();
                m_InstanceIdToIndex.Add(instanceId, index);
                m_InstantiatedObjects[index] = new List<GameObject>();
                m_NumObjectsActive[index] = 0;
                ++index;
            }
        }

        public GameObject GetOrInstantiate(GameObject prefab)
        {
            if (!m_InstanceIdToIndex.TryGetValue(prefab.GetInstanceID(), out var index))
            {
                throw new ArgumentException($"Prefab {prefab.name} (ID: {prefab.GetInstanceID()}) is not in cache.");
            }

            ++NumObjectsActive;
            if (m_NumObjectsActive[index] < m_InstantiatedObjects[index].Count)
            {
                var nextInCache = m_InstantiatedObjects[index][m_NumObjectsActive[index]];
                ++m_NumObjectsActive[index];
                return nextInCache;
            }
            else
            {
                ++NumObjectsInCache;
                var newObject = Object.Instantiate(prefab, m_CacheParent);
                ++m_NumObjectsActive[index];
                m_InstantiatedObjects[index].Add(newObject);
                return newObject;
            }
        }

        public void ResetAllObjects()
        {
            using (s_ResetAllObjectsMarker.Auto())
            {
                NumObjectsActive = 0;
                for (var i = 0; i < m_InstantiatedObjects.Length; ++i)
                {
                    m_NumObjectsActive[i] = 0;
                    foreach (var obj in m_InstantiatedObjects[i])
                    {
                        // Position outside the frame
                        obj.transform.localPosition = new Vector3(10000, 0, 0);
                    }
                }
            }
        }
    }
}