Pool.cs

using System.Collections.Generic;
using UnityEngine;

public class Pool : MonoBehaviour
{
    private const int DEFUALT_POOL_SIZE = 100;

    private static Dictionary<IPoolable, Pool> pools = new Dictionary<IPoolable, Pool>();

	public static Pool GetPool(IPoolable prefab)
	{
        if (pools.ContainsKey(prefab))
        {
            if (pools[prefab] != null)
                return pools[prefab];
            else
                pools.Remove(prefab);
        }

		var pool = new GameObject("Pool-" + (prefab as Component).name).AddComponent<Pool>();
		pool.Initialize(prefab);
		pools.Add(prefab, pool);
		return pool;
	}

    public static Pool Prewarm(IPoolable prefab, int initialSize)
    {
        if (pools.ContainsKey(prefab))
        {
            if (pools[prefab] != null)
            {
                Debug.LogError("Pool already created, can't prewarm");
                return pools[prefab];
            }
            else
                pools.Remove(prefab);
        }

        var pool = new GameObject("Pool-" + (prefab as Component).name).AddComponent<Pool>();
        pool.Initialize(prefab, initialSize);
        pools.Add(prefab, pool);
        return pool;
    }

    private GameObject prefab;
    
	private Queue<IPoolable> objects = new Queue<IPoolable>();
	private List<IPoolable> disabledObjects = new List<IPoolable>();

	private void Initialize(IPoolable poolablePrefab, int initialSize = DEFUALT_POOL_SIZE)
	{
		this.prefab = (poolablePrefab as Component).gameObject;
		for (int i = 0; i < initialSize; i++)
		{
			var pooledObject = (Instantiate(this.prefab) as GameObject).GetComponent<IPoolable>();
			(pooledObject as Component).gameObject.name += " " + i;

			pooledObject.OnDestroyEvent += () => AddObjectToAvailable(pooledObject);

            (pooledObject as Component).gameObject.SetActive(false);
        }
	}

	private void AddObjectToAvailable(IPoolable pooledObject)
	{
		disabledObjects.Add(pooledObject);
		objects.Enqueue(pooledObject);
	}

	private IPoolable Get()
	{
        lock (this)
        {
            if (objects.Count == 0)
            {
                int amountToGrowPool = Mathf.Max((disabledObjects.Count / 10), 1);
                Initialize(this.prefab.GetComponent<IPoolable>(), amountToGrowPool);
            }

            var pooledObject = objects.Dequeue();

            return pooledObject;
        }
	}

	public IPoolable Get(Vector3 position, Quaternion rotation)
	{
		var pooledObject = Get();

        (pooledObject as Component).transform.position = position;
		(pooledObject as Component).transform.rotation = rotation;
		(pooledObject as Component).gameObject.SetActive(true);

        return pooledObject;
	}

	private void Update()
	{
		MakeDisabledObjectsChildren();
	}

	private void MakeDisabledObjectsChildren()
	{
		if (disabledObjects.Count > 0)
		{
			foreach (var pooledObject in disabledObjects)
			{
				(pooledObject as Component).transform.SetParent(transform);
			}

			disabledObjects.Clear();
		}
	}
}