The last game object pool you will ever need... maybe.

ComponentPool.cs

using System.Collections.Generic;
using UnityEngine;


public class ComponentPool<T> where T : Component
{
    static ComponentPool<T> Instance = new ComponentPool<T>();

    Dictionary<int, Stack<T>> pools = new Dictionary<int, Stack<T>>();
    Dictionary<int, int> instances = new Dictionary<int, int>();

    static public void Prewarm(T prefab, int count)
    {
        var pool = Instance.GetPool(prefab.GetInstanceID());
        for (var i = 0; i < count; i++)
            Instance.CreateInstance(prefab, pool);
    }

    static public T Take(T prefab)
    {
        var poolKey = prefab.GetInstanceID();
        var pool = Instance.GetPool(poolKey);
        T g;
        if (pool.Count == 0)
            g = Instance.CreateInstance(prefab, pool);
        else
            g = pool.Pop();
        Instance.instances[g.GetInstanceID()] = poolKey;
        g.gameObject.SetActive(true);
        return g;
    }

    static public void Return(T instance)
    {
        if (instance == null)
            Debug.Log("Cannot return a null instance.");
        else
        {
            int poolKey;
            var instanceKey = instance.GetInstanceID();
            if (Instance.instances.TryGetValue(instanceKey, out poolKey))
            {
                var pool = Instance.pools[poolKey];
                instance.gameObject.SetActive(false);
                Instance.instances.Remove(instanceKey);
                pool.Push(instance);
            }
            else
            {
                Debug.LogWarning("Cannot return an instance that was not taken from a pool.", instance.gameObject);
            }
        }
    }

    T CreateInstance(T prefab, Stack<T> pool)
    {
        var g = GameObject.Instantiate(prefab);
        g.gameObject.SetActive(false);
        return g;
    }

    Stack<T> GetPool(int key)
    {
        Stack<T> pool;
        if (!pools.TryGetValue(key, out pool))
            pool = pools[key] = new Stack<T>();
        return pool;
    }
}