Creating entities in Specs

entities.rs

impl<'a> System<'a> for EntitiyCreator {
    type SystemData = (Entities<'a>, WriteStorage<'a, Pos>);
  
    fn run(&mut self, (entities, pos): Self::SystemData) {
        let a = entities.create();
        let b = entities.create();
      
        pos.insert(a, Pos::new(2, 4));
        pos.insert(b, Pos::new(3, 5));
    }
}

// Now, if you want to insert many components for these new entities,
// it might be better to use `LazyUpdate` in order to avoid fetching many
// storages mutably:

impl<'a> System<'a> for LazyCreator {
    type SytemData = (Entities<'a>, Fetch<'a, LazyUpdate>);
  
    fn run(&mut self, (entities, lazy): Self::SystemData) {
        let a = entities.create();
        // These updates will be applied at the end of this frame
        lazy.insert(a, Pos::new(2, 5));
        lazy.insert(a, Vel::new(0, 1));
    }
}