Trait Component

pub trait Component: 'static {
    type Mutability: MutabilityMarker;
}

Types which store data on entities.

A Component is a piece of data which can be attached to an entity. An entity can have any combination of components, but cannot have more than one component of the same type.

To add a component to an entity, use the Insert event. To access components from handlers, use the Fetcher handler parameter.

Deriving

The Component trait can be implemented automatically by using the associated derive macro. However, the type must still satisfy the 'static bound to do so.

use evenio::prelude::*;

// Component with some data.
#[derive(Component)]
struct Username(String);

// Component without data, known as a "marker" or "tag" component.
struct Invisible;

// Derive it on structs with named fields.
#[derive(Component)]
struct Position {
    x: f32,
    y: f32,
    z: f32,
}

// ...and on enums.
#[derive(Component)]
enum FriendStatus {
    Friendly,
    Neutral,
    Unfriendly,
}

// Components can be immutable, which disallows mutable references
// to the component once it's attached to an entity.
#[derive(Component)]
#[component(immutable)] // Override the default mutability.
struct FooCounter(i32);

Required Associated Types

type Mutability: MutabilityMarker

Indicates if this event is Mutable or Immutable.

Immutable components disallow mutable references, which can be used to ensure components are only modified via events.

Implementors