Get and Modify Components

To access or update components you can use Get::get. It'll work with both shared and exclusive views.

let mut world = World::new();

let id = world.add_entity((0u32, 1usize));

let (mut u32s, mut usizes) = world.borrow::<(ViewMut<u32>, ViewMut<usize>)>().unwrap();

*(&mut usizes).get(id).unwrap() += 1;

let (mut i, j) = (&mut u32s, &usizes).get(id).unwrap();
*i += *j as u32;

u32s[id] += 1;

When using a single view, if you are certain an entity has the desired component, you can access it via index.

Fast Get

Using get with &mut ViewMut<T> will return Mut<T>. This struct helps fine track component modification.
FastGet::fast_get can be used to opt out of this fine tracking and get back &mut T.