Object Pooling

using UnityEngine;
using System.Collections.Generic;

public class BulletPool : MonoBehaviour
{
  public GameObject bulletPrefab;
  public int poolSize = 30;
  readonly Queue<GameObject> pool = new Queue<GameObject>();

  void Awake()
  {
      // Pre-warm: create and disable
      for (int i = 0; i < poolSize; i++)
      {
          var go = Instantiate(bulletPrefab);
          go.SetActive(false);
          go.transform.SetParent(transform);
          pool.Enqueue(go);
      }
  }

  public GameObject Get(Vector3 pos, Quaternion rot)
  {
      var go = pool.Count > 0
          ? pool.Dequeue()
          : Instantiate(bulletPrefab); // Expand if empty
      go.transform.SetPositionAndRotation(pos, rot);
      go.SetActive(true);
      return go;
  }

  public void Release(GameObject go)
  {
      go.SetActive(false);
      pool.Enqueue(go);
  }
}

using UnityEngine;
using UnityEngine.Pool;

public class AdvancedBulletPool : MonoBehaviour
{
  public Bullet bulletPrefab;

  ObjectPool<Bullet> pool;

  void Awake()
  {
      pool = new ObjectPool<Bullet>(
          createFunc:   () => Instantiate(bulletPrefab, transform),
          actionOnGet:  b => { b.gameObject.SetActive(true); b.OnGet(); },
          actionOnRelease: b => { b.gameObject.SetActive(false); b.OnRelease(); },
          actionOnDestroy: b => Destroy(b.gameObject), // When the pool is full
          collectionCheck: false,  // Skip duplicate checks (production)
          defaultCapacity: 20,
          maxSize:         50
      );
  }

  public Bullet Spawn(Vector3 pos, Vector3 dir)
  {
      var bullet = pool.Get();
      bullet.transform.position = pos;
      bullet.Init(dir, pool); // Bullet calls pool.Release(this) when done
      return bullet;
  }

  public void LogStats()
  {
      Debug.Log($"Pool: {pool.CountActive} active / {pool.CountAll} total");
  }
}