Function valence::prelude::any_with_component

pub fn any_with_component<T>(query: Query<'_, '_, (), With<T>>) -> bool
where
    T: Component,

A Condition-satisfying system that returns true if there are any entities with the given component type.

Example

app.add_systems(
    my_system.run_if(any_with_component::<MyComponent>),
);

#[derive(Component)]
struct MyComponent;

fn my_system(mut counter: ResMut<Counter>) {
    counter.0 += 1;
}

// No entities exist yet with a `MyComponent` component so `my_system` won't run
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 0);

world.spawn(MyComponent);

// An entities with `MyComponent` now exists so `my_system` will run
app.run(&mut world);
assert_eq!(world.resource::<Counter>().0, 1);