Iterate over combinations of entities

fn interact_bodies(mut query: Query<(&Mass, &GlobalTransform, &mut Acceleration)>) {
    let mut iter = query.iter_combinations_mut();
    while let Some([(Mass(m1), transform1, mut acc1), (Mass(m2), transform2, mut acc2)]) =
        iter.fetch_next()
    {
        let delta = transform2.translation() - transform1.translation();
        let distance_sq: f32 = delta.length_squared();

        let f = GRAVITY_CONSTANT / distance_sq;
        let force_unit_mass = delta * f;
        acc1.0 += force_unit_mass * *m2;
        acc2.0 -= force_unit_mass * *m1;
    }
}