object-pooling

Object Pooling

Every Instantiate() allocates memory. Every Destroy() triggers GC. Pool objects you create and destroy frequently: projectiles, particles, enemies, pickups, audio sources.

Unity Built-In ObjectPool (2021+)

using UnityEngine.Pool;

public sealed class ProjectilePool : MonoBehaviour
{
    [SerializeField] private Projectile _prefab;
    [SerializeField] private int _defaultCapacity = 20;
    [SerializeField] private int _maxSize = 100;

    private ObjectPool<Projectile> _pool;

    private void Awake()
    {
        _pool = new ObjectPool<Projectile>(
            createFunc: CreateProjectile,
            actionOnGet: OnGetProjectile,
            actionOnRelease: OnReleaseProjectile,
            actionOnDestroy: OnDestroyProjectile,
            collectionCheck: false,
            defaultCapacity: _defaultCapacity,
            maxSize: _maxSize
        );
    }

    public Projectile Get() => _pool.Get();

    public void Release(Projectile projectile) => _pool.Release(projectile);

    private Projectile CreateProjectile()
    {
        Projectile projectile = Instantiate(_prefab);
        projectile.SetPool(this);
        return projectile;
    }

    private void OnGetProjectile(Projectile projectile)
    {
        projectile.gameObject.SetActive(true);
    }

    private void OnReleaseProjectile(Projectile projectile)
    {
        projectile.gameObject.SetActive(false);
    }

    private void OnDestroyProjectile(Projectile projectile)
    {
        Destroy(projectile.gameObject);
    }
}

// Projectile returns itself to pool
public sealed class Projectile : MonoBehaviour
{
    private ProjectilePool _pool;

    public void SetPool(ProjectilePool pool) => _pool = pool;

    public void ReturnToPool()
    {
        _pool.Release(this);
    }
}

Warm-Up (Pre-Spawn)

Pre-instantiate objects during loading to avoid runtime hitches:

private void Start()
{
    // Pre-warm the pool
    List<Projectile> temp = new List<Projectile>();
    for (int i = 0; i < _defaultCapacity; i++)
    {
        temp.Add(_pool.Get());
    }
    for (int i = 0; i < temp.Count; i++)
    {
        _pool.Release(temp[i]);
    }
    temp.Clear();
}