Macro gecs::ecs_component_id

macro_rules! ecs_component_id {
    {...} => { ... };
}

Returns the compile-time ID of a given component in its archetype.

ecs_component_id!(Component);            // Can be used in a query body
ecs_component_id!(Component, Archetype); // If used outside of a query

The ecs_component_id! returns the compile-time ID (as a u8) of a given component in an archetype. If used in a query, the archetype parameter defaults to MatchedArchetype, which is the type alias automatically set for each query referencing the current matched archetype for the current execution of the query body.

This is a const operation, and can be used to parameterize const generics.

By default, component IDs are assigned sequentially starting at 0, with a maximum of 255. Component IDs can also be manually set using the #[component_id(N)] attribute on elements of the component list in an ecs_archetype! declaration within ecs_world!. Like enum discriminants, components without this attribute will count up from the last manually set ID.

Example

use gecs::prelude::*;

pub struct CompA;
pub struct CompB;
pub struct CompC;

ecs_world! {
    ecs_archetype!(
        ArchFoo,
        5,
        CompA, // = 0
        CompC, // = 1
    );

    ecs_archetype!(
        ArchBar,
        5,
        #[component_id(6)]
        CompA, // = 6
        CompB, // = 7 (Implicit)
        CompC, // = 8 (Implicit)
    );

    ecs_archetype!(
        ArchBaz,
        5,
        CompA, // = 0 (Implicit)
        CompB, // = 1 (Implicit)
        #[component_id(200)]
        CompC, // = 200
    );
}

fn main() {
    let mut world = EcsWorld::default();

    let entity_a = world.archetype_mut::<ArchFoo>().create((CompA, CompC));
    let entity_b = world.archetype_mut::<ArchBar>().create((CompA, CompB, CompC));
    let entity_c = world.archetype_mut::<ArchBaz>().create((CompA, CompB, CompC));

    ecs_find!(world, entity_a, |_: &CompC| {
        assert_eq!(ecs_component_id!(CompC), 1);
    });

    ecs_find!(world, entity_b, |_: &CompC| {
        assert_eq!(ecs_component_id!(CompC), 8);
    });

    ecs_find!(world, entity_c, |_: &CompC| {
        assert_eq!(ecs_component_id!(CompC), 200);
    });

    assert_eq!(ecs_component_id!(CompC, ArchFoo), 1);
    assert_eq!(ecs_component_id!(CompC, ArchBar), 8);
    assert_eq!(ecs_component_id!(CompC, ArchBaz), 200);
}