Struct moonshine_util::expect::Expect

pub struct Expect<T: QueryData>(/* private fields */);

A QueryData decorator which panics if its inner query does not match.

Usage

This decorator is useful for preventing systems from silently skipping over entities which may erroneously not a query.

Consider the following erroneous example:

use bevy::prelude::*;

#[derive(Component)]
struct A;

#[derive(Component)]
struct B;

// A and B are always expected to be inserted together:
#[derive(Bundle)]
struct AB {
    a: A,
    b: B,
}

fn bad_system(mut commands: Commands) {
    commands.spawn(A); // Spawn A without B!
}

fn unsafe_system(q: Query<(&A, &B)>) {
    for _ in q.iter() {
        // An instance of `A` does exist.
        // But because `A` does not exist *with* `B`, this system skips over it silently.
    }
}

This problem can be solved with Expect:

use moonshine_util::expect::Expect;

fn safe_system(q: Query<(&A, Expect<&B>)>) {
    for _ in q.iter() {
       // This system will panic if it finds an instance of `A` without `B`.
    }
}

Trait Implementations

impl<T: QueryData> QueryData for Expect<T>

type ReadOnly = Expect<<T as QueryData>::ReadOnly>

The read-only variant of this QueryData, which satisfies the ReadOnlyQueryData trait.

impl<T: QueryData> WorldQuery for Expect<T>

type Fetch<'w> = ExpectFetch<'w, T>

Per archetype/table state used by this WorldQuery to fetch Self::Item

type Item<'w> = <T as WorldQuery>::Item<'w>

The item returned by this WorldQuery For QueryData this will be the item returned by the query. For QueryFilter this will be either (), or a bool indicating whether the entity should be included or a tuple of such things.

type State = <T as WorldQuery>::State

State used to construct a Self::Fetch. This will be cached inside QueryState, so it is best to move as much data / computation here as possible to reduce the cost of constructing Self::Fetch.

fn shrink<'wlong: 'wshort, 'wshort>( item: Self::Item<'wlong>, ) -> Self::Item<'wshort>

This function manually implements subtyping for the query items.

const IS_DENSE: bool = T::IS_DENSE

Returns true if (and only if) every table of every archetype matched by this fetch contains all of the matched components. This is used to select a more efficient “table iterator” for “dense” queries. If this returns true, WorldQuery::set_table must be used before WorldQuery::fetch can be called for iterators. If this returns false, WorldQuery::set_archetype must be used before WorldQuery::fetch can be called for iterators.

unsafe fn init_fetch<'w>( world: UnsafeWorldCell<'w>, state: &T::State, last_run: Tick, this_run: Tick, ) -> ExpectFetch<'w, T>

Creates a new instance of this fetch.

unsafe fn set_archetype<'w>( fetch: &mut ExpectFetch<'w, T>, state: &T::State, archetype: &'w Archetype, table: &'w Table, )

Adjusts internal state to account for the next Archetype. This will always be called on archetypes that match this WorldQuery.

unsafe fn set_table<'w>( fetch: &mut ExpectFetch<'w, T>, state: &T::State, table: &'w Table, )

Adjusts internal state to account for the next Table. This will always be called on tables that match this WorldQuery.

unsafe fn fetch<'w>( fetch: &mut Self::Fetch<'w>, entity: Entity, table_row: TableRow, ) -> Self::Item<'w>

Fetch Self::Item for either the given entity in the current Table, or for the given entity in the current Archetype. This must always be called after WorldQuery::set_table with a table_row in the range of the current Table or after WorldQuery::set_archetype with a entity in the current archetype.

fn update_component_access( state: &T::State, access: &mut FilteredAccess<ComponentId>, )

Adds any component accesses used by this WorldQuery to access.

fn get_state(components: &Components) -> Option<Self::State>

Attempts to initialize a State for this WorldQuery type using read-only access to Components.

fn init_state(world: &mut World) -> T::State

Creates and initializes a State for this WorldQuery type.

fn matches_component_set( _state: &T::State, _set_contains_id: &impl Fn(ComponentId) -> bool, ) -> bool

Returns true if this query matches a set of components. Otherwise, returns false.

fn set_access(_state: &mut Self::State, _access: &FilteredAccess<ComponentId>)

Sets available accesses for implementors with dynamic access such as FilteredEntityRef or FilteredEntityMut.

impl<T: ReadOnlyQueryData> ReadOnlyQueryData for Expect<T>