The ECS Mindset
Entities, components, and systems.
What ECS Solves
Bevy is built on the Entity Component System (ECS) pattern. Instead of deep inheritance hierarchies, you compose behavior from small, independent pieces of data.
This data-oriented design keeps memory layout cache-friendly and lets the engine parallelize work across CPU cores almost for free.
Entities Are Just IDs
An entity is nothing but a lightweight identifier — a generational index. It owns no data and has no behavior on its own.
Think of it as a key in a database row. Components attached to that key give the entity meaning, like "Player" or "Bullet".
// An Entity is a tiny handle
struct Entity {
index: u32,
generation: u32,
}