Is there a way to see (and get an Entity from) the world from a rust legion ECS system?

I'm following a rust tutorial that uses the Specs ECS, and I'm trying to implement it using the legion ECS instead. I love legion and everything went smoothly until I faced a problem.

I'm not sure how to formulate my question. What I am trying to do is create a system that iterates on every entity that has e.g. ComponentA and ComponentB, but that also checks if the entity has ComponentC and do something special if it is the case.

I can do it like so using Specs (example code):

// Uses Specs
pub struct SystemA {}

impl<'a> System<'a> for SystemA {
    type SystemData = ( Entities<'a>,
                        WriteStorage<'a, ComponentA>, 
                        ReadStorage<'a, ComponentB>,
                        ReadStorage<'a, ComponentC>);

    fn run(&mut self, data : Self::SystemData) {
        let (entities, mut compA, compB, compC) = data;

        // Finding all entities with ComponentA and ComponentB
        for (ent, compA, compB) in (&entities, &mut compA, &compB).join() {
            // Do stuff with compA and compB

            // Check if Entity also has ComponentC
            let c : Option<&ComponentC> = compC.get(ent);

            if let Some(c) = c {
                // Do something special with entity if it also has ComponentC
            }
        }
    }
}

I have a hard time translating this to using legion (currently using the latest 0.4.0 version). I don't know how to get the other components that the current entity has. Here is the code I have:

#[system(for_each)]
pub fn systemA(entity: &Entity, compA: &mut compA, compB: &mut ComponentB) {
    // Do stuff with compA and compB

    // How do I check if entity has compC here?

}

The entity in the system above only contains its ID. How do I access the list of components this entity has without the World? Or is there a way to access the World in a system in legion? Or any other way to achieve the same as the Specs version?

Thanks!

you can use Option<...> to optional component.

#[system(for_each)]
pub fn systemA(entity: &Entity, compA: &mut compA, compB: &mut ComponentB, compC: Option<&ComponentC>) {
    ...
    if let Some(compC) = compC {
        // this entity has compC
        ...