public interface ICollider
    {
        Collider MyCollider { get; }
        void OnMyCollisionEnter(ICollider otherCollider);
        void OnMyCollisionStay(ICollider otherCollider);
        void OnMyCollisionExit(ICollider collider);
    }

    public class CollisionsDetector : MonoBehaviour
    {
        private const int CollidersInitialCapacity = 20;

        private int collidersCount;
        private List<ICollider> colliders;
        private Dictionary<Tuple<ICollider, ICollider>, bool> collisions;

        private void Start()
        {
            collidersCount = 0;
            colliders = new List<ICollider>(CollidersInitialCapacity);
            collisions = new Dictionary<Tuple<ICollider, ICollider>, bool>(CollidersInitialCapacity * CollidersInitialCapacity);
        }

        private void OnDestroy()
        {
            collidersCount = 0;
            colliders = null;
            collisions = null;
        }

        public void AddCollider(ICollider collider)
        {
            CheckCollisions(collider);
            colliders.Add(collider);
            collidersCount++;
        }

        public void RemoveCollider(ICollider collider)
        {
            colliders.Remove(collider);
            collidersCount--;
            RemoveCollisions(collider);
        }

        private void FixedUpdate()
        {
            CheckCollisions();
        }

        private void CheckCollisions()
        {
            for (int i = 0; i < collidersCount; i++)
            {
                ICollider collider = colliders[i];
                for (int j = i + 1; j < collidersCount; j++)
                {
                    ICollider otherCollider = colliders[j];
                    CheckCollision(collider, otherCollider);
                }
            }
        }

        private void CheckCollision(ICollider collider, ICollider otherCollider)
        {
            bool areColliding = collider.MyCollider.bounds.Intersects(otherCollider.MyCollider.bounds);
            Tuple<ICollider, ICollider> tuple = Tuple.Create(collider, otherCollider);
            bool whereColliding;
            collisions.TryGetValue(tuple, out whereColliding);
            collisions[tuple] = areColliding;
            NotifyCollisionEvents(collider, otherCollider, areColliding, whereColliding);
        }

        private void NotifyCollisionEvents(ICollider collider, ICollider otherCollider, bool areColliding, bool whereColliding)
        {
            if (areColliding)
            {
                if (!whereColliding)
                {
                    collider.OnMyCollisionEnter(otherCollider);
                    otherCollider.OnMyCollisionEnter(collider);
                }
                else
                {
                    collider.OnMyCollisionStay(otherCollider);
                    otherCollider.OnMyCollisionStay(collider);
                }
            }
            else if (whereColliding)
            {
                collider.OnMyCollisionExit(otherCollider);
                otherCollider.OnMyCollisionExit(collider);
            }
        }

        private void CheckCollisions(ICollider collider)
        {
            for (int i = 0; i < collidersCount; i++)
            {
                ICollider otherCollider = colliders[i];
                CheckCollision(otherCollider, collider);
            }
        }

        private void RemoveCollisions(ICollider collider)
        {
            for (int i = 0; i < collidersCount; i++)
            {
                ICollider otherCollider = colliders[i];
                Tuple<ICollider, ICollider> tuple = Tuple.Create(collider, otherCollider);
                bool whereColliding;
                collisions.TryGetValue(tuple, out whereColliding);
                collisions.Remove(tuple);
                if (whereColliding)
                    otherCollider.OnMyCollisionExit(collider);
            }
        }
    }