The Entity-Component-System (ECS) model has become the industry standard for game engine design. However, most ECS implementations rely heavily on query-based systems to retrieve relevant entities every frame — an approach that introduces unnecessary overhead and runtime cost.

That's why I propose an alternative architecture: the Reactive ECS.

Instead of querying entities each frame, systems subscribe once to specific combinations of components. A centralized ECSManager then conditionally dispatches the relevant entities to each system, based on these subscriptions. In other words, the only "query" is done up-front, at subscription time.

🚀 Benefits of this approach:

• Zero per-frame query cost: Systems receive only what they need, when they need it.
• Modular and dynamic: Entities and systems can be added or removed at runtime; the subscription logic handles everything.
• Scalable and performant: 1 million entities dispatched to 3 systems in just 980 ns, on a dual-thread CPU.
• Better memory locality: Archetype grouping makes processing cache-friendly.
• Naturally parallelizable: Systems are decoupled and only receive their relevant data.

You can check the full implementation and architecture (written in Julia) here:

👉 https://github.com/Gesee-y/RECS.jl

Feedback and contributions are welcome!