Unity Object Pool

ObjectPool.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ObjectPool : MonoBehaviour
{
    [System.Serializable]
    public struct PoolConfiguration
    {
        public string objectName;
        public PoolConfigurationSettings settings;
    }

    [System.Serializable]
    public struct PoolConfigurationSettings
    {
        public GameObject objectTemplate;
        public int initialPoolSize;
        public int poolSizeIncrement;
    }

    //Used to allow the developer to configure the different pools in the inspector
    public PoolConfiguration[] poolConfigurations;

    //Dictionary to link an object name to a 'template' and other pool config settings
    private Dictionary<string, PoolConfigurationSettings> poolDict;

    //Dictionary to keep track of our instances so we can easily go through all instances
    //of a certain type, bypassing the transform hierarchy (useful if there are multiple pools)
    private Dictionary<string, List<GameObject>> instancesDict;

    void Start()
    {
        poolDict = new Dictionary<string, PoolConfigurationSettings>();
        instancesDict = new Dictionary<string, List<GameObject>>();

        foreach (PoolConfiguration config in poolConfigurations)
        {
            poolDict.Add(config.objectName, config.settings);
            instancesDict.Add(config.objectName, new List<GameObject>());

            //Initialize this pool
            Expand(config.objectName, config.settings.initialPoolSize);
        }
    }

    GameObject[] Expand(string objectName, int amount)
    {
        GameObject template = poolDict[objectName].objectTemplate;
        GameObject[] freshInstances = new GameObject[amount];

        for (int i = 0; i < amount; i++)
        {
            var inst = Instantiate(template, transform, true);
            inst.SetActive(false);

            freshInstances[i] = inst;
            instancesDict[objectName].Add(inst);
        }

        return freshInstances;
    }

    public GameObject Get(string objectName)
    {
        //Find the first available object
        foreach (GameObject go in instancesDict[objectName])
        {
            if (!go.activeInHierarchy)
            {
                return go;
            }
        }

        //If we get this far, we didn't find it, 
        //which means we should expand the pool and try again
        GameObject freshInstance = Expand(objectName, poolDict[objectName].poolSizeIncrement)[0];

        return freshInstance;
    }
}