Trait Traversal

pub trait Traversal<D: ?Sized>: ReadOnlyQueryData {
    // Required method
    fn traverse(item: Self::Item<'_>, data: &D) -> Option<Entity>;
}

A component that can point to another entity, and which can be used to define a path through the ECS.

Traversals are used to specify the direction of event propagation in observers. The default query is ().

Infinite loops are possible, and are not checked for. While looping can be desirable in some contexts (for example, an observer that triggers itself multiple times before stopping), following an infinite traversal loop without an eventual exit will cause your application to hang. Each implementer of Traversal for documenting possible looping behavior, and consumers of those implementations are responsible for avoiding infinite loops in their code.

Traversals may be parameterized with additional data. For example, in observer event propagation, the parameter D is the event type given in Trigger<E>. This allows traversal to differ depending on event data.

Required Methods

fn traverse(item: Self::Item<'_>, data: &D) -> Option<Entity>

Returns the next entity to visit.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl<D> Traversal<D> for ()

fn traverse(_: Self::Item<'_>, _data: &D) -> Option<Entity>

impl<R: Relationship, D> Traversal<D> for &R

This provides generalized hierarchy traversal for use in event propagation.

Warning

Traversing in a loop could result in infinite loops for relationship graphs with loops.

fn traverse(item: Self::Item<'_>, _data: &D) -> Option<Entity>

Implementors