brakeys_object_pooling

using System.Collections.Generic;
using UnityEngine;

public class CustomObjectPooling : MonoBehaviour {

    [System.Serializable]
    public class ObjPool
    {
        public string objKey;
        public GameObject objPrefab;
        public int size;
    }
    GameManager gameInstance;
    public static CustomObjectPooling instance;

    public List<ObjPool> objPools;
    public Dictionary<string, Queue<GameObject>> objectPoolDictionary;

    private void Awake()
    {
        if(instance != null)
        {
            Debug.Log("already have objectpool");
            return;
        }
        instance = this;
    }

    // Use this for initialization
    void Start () {
        gameInstance = GameManager.gameInstance;
        objectPoolDictionary = new Dictionary<string, Queue<GameObject>>();

        foreach(ObjPool objPool in objPools)
        {
            Queue<GameObject> objectPool = new Queue<GameObject>();

            for(int i = 0; i < objPool.size; i++)
            {
                GameObject obj = Instantiate(objPool.objPrefab);
                obj.SetActive(false);
                objectPool.Enqueue(obj);
            }
            objectPoolDictionary.Add(objPool.objKey, objectPool);
        }
    }

    public GameObject SpawnObjFromPool(string _objKey, Vector3 position, Quaternion rotation)
    {
        if (!objectPoolDictionary.ContainsKey(_objKey))
        {
            Debug.LogWarning("Pool with key" + _objKey + "doesn't exist");
            return null;
        }

        GameObject objectSpawned = objectPoolDictionary[_objKey].Dequeue();

        objectSpawned.SetActive(true);
        objectSpawned.transform.position = position;
        objectSpawned.transform.rotation = rotation;

        IPooledObject pooledObject = objectSpawned.GetComponent<IPooledObject>();

        if(pooledObject != null)
        {
            pooledObject.SpawnEnemy();
            gameInstance.enemiesAlive++;
        }

        objectPoolDictionary[_objKey].Enqueue(objectSpawned);

        return objectSpawned;
    }

}

WaveSpawner.cs

......
    IEnumerator SpawnWaveFirstLocation()
    {
        GameObject objSpawned;
        Wave wave = waves[waveNumber];
        for(int i = 0; i < wave.count; i++)
        {
            enemiesAlive++;
            objSpawned = objectPooler.SpawnObjFromPool(wave.enemyNameKey, transform.position, Quaternion.identity);
            yield return new WaitForSeconds(1f / wave.rate);
        }
    }