Struct WorldHasher 

pub struct WorldHasher { /* private fields */ }

The canonical world hash: which state the digest covers, and in what order.

The fold order is pinned in the module docs. An empty hasher digests the entity list alone, which is a real check in a game whose state is its entities, but most callers register the components and resources that decide gameplay:

let mut hasher = WorldHasher::new();
hasher.register::<Height>(|height, hash| hash.f32(height.0));
hasher.register_resource::<Score>(|score, hash| hash.u32(score.0));

Implementations

impl WorldHasher

pub fn new() -> Self

A hasher that folds the entity list and nothing else.

pub fn register<C: Component>( &mut self, hash_value: impl Fn(&C, &mut Hash64) + Send + Sync + 'static, ) -> &mut Self

Registers a component: one (entity, value) fold per entity that has it.

Write the value’s fields in a fixed order. A float folds its bits (hash.f32(value)), so the sign of zero and a NaN payload are covered exactly; a field left out is a field the digest cannot report.

pub fn register_hashed<C: Component + Hash>(&mut self) -> &mut Self

register for a component whose own Hash implementation is yours.

The fold is whatever Hash writes, and every integer writer is pinned by Hash64, but a Hash impl from std or from a dependency may change its byte layout in a later release. For a digest a save file or a golden test pins, write the fields explicitly with register.

pub fn register_resource<R: Resource>( &mut self, hash_value: impl Fn(&R, &mut Hash64) + Send + Sync + 'static, ) -> &mut Self

Registers a resource: a presence byte, then the value hash when it exists.

Presence is state of its own, so a resource missing from one run and present in the other folds differently even when its payload is a zero.

pub fn register_hashed_resource<R: Resource + Hash>(&mut self) -> &mut Self

register_resource for a resource whose own Hash implementation is yours.

pub fn hash(&self, world: &World) -> u64

The canonical digest of world: one number that moves whenever any registered state moves.

Folds in the order the module docs pin, which is not bevy_ecs’s iteration order, so a run that reaches the same state through a different spawn/despawn history digests the same.

Trait Implementations

impl Clone for WorldHasher

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Default for WorldHasher

fn default() -> Self

Returns the “default value” for a type.