Bevy 0.19 — ECS Components

When to use this skill

• Defining a new Component for game state.
• Bundling components via #[require(...)] (the modern replacement for "bundles").
• Reacting to component lifecycle: spawning, despawning, inserting, removing.
• Observers — reacting to entity-targeted events with On<E>.
• Choosing storage: Table (default, fast iteration) vs SparseSet (fast add/remove).

Canonical pattern

use bevy::prelude::*;

// 1. Plain components.
#[derive(Component, Default)]
struct Health(f32);