Vector of Generic Structs in Rust

Question

I am creating an entity component system in Rust, and I would like to be able to store a Vec of components for each different Component type:

pub trait Component {}

struct ComponentList<T: Component> {
    components: Vec<T>,
}

Is it possible to create a collection of these ComponentLists?

struct ComponentManager {
    component_lists: Vec<ComponentList<_>>, // This does not work
}

This is intended to make it faster to retrieve a list of a certain Component type, as all instances of a certain type of component will be in the same ComponentList.

Answer 1

Create a trait that each ComponentList<T> will implement but that will hide that T. In that trait, define any methods you need to operate on the component list (you will not be able to use T, of course, you'll have to use trait objects like &Component).

trait AnyComponentList {
    // Add any necessary methods here
}

impl<T: Component> AnyComponentList for ComponentList<T> {
    // Implement methods here
}

struct ComponentManager {
    component_lists: Vec<Box<AnyComponentList>>,
}

---

If you would like to have efficient lookup of a ComponentList<T> based on T from the ComponentManager, you might want to look into anymap or typemap instead. anymap provides a simple map keyed by the type (i.e. you use a type T as the key and store/retrieve a value of type T). typemap generalizes anymap by associated keys of type K with values of type K::Value.