Struct Populated

pub struct Populated<'w, 's, D: QueryData, F: QueryFilter = ()>(/* private fields */);

System parameter that works very much like Query except it always contains at least one matching entity.

This SystemParam fails validation if no matching entities exist. This will cause systems that use this parameter to be skipped.

Much like Query::is_empty the worst case runtime will be O(n) where n is the number of potential matches. This can be notably expensive for queries that rely on non-archetypal filters such as Added or Changed which must individually check each query result for a match.

See Query for more details.

Implementations

impl<'w, 's, D: QueryData, F: QueryFilter> Populated<'w, 's, D, F>

pub fn into_inner(self) -> Query<'w, 's, D, F>

Returns the inner item with ownership.

Methods from Deref<Target = Query<'w, 's, D, F>>

pub fn to_readonly(&self) -> Query<'_, 's, D::ReadOnly, F>

Returns another Query from this that fetches the read-only version of the query items.

For example, Query<(&mut D1, &D2, &mut D3), With<F>> will become Query<(&D1, &D2, &D3), With<F>>. This can be useful when working around the borrow checker, or reusing functionality between systems via functions that accept query types.

pub fn reborrow(&mut self) -> Query<'_, 's, D, F>

Returns a new Query reborrowing the access from this one. The current query will be unusable while the new one exists.

Example

For example this allows to call other methods or other systems that require an owned Query without completely giving up ownership of it.

fn helper_system(query: Query<&ComponentA>) { /* ... */}

fn system(mut query: Query<&ComponentA>) {
    helper_system(query.reborrow());
    // Can still use query here:
    for component in &query {
        // ...
    }
}

pub fn iter(&self) -> QueryIter<'_, 's, D::ReadOnly, F>

Returns an Iterator over the read-only query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Example

Here, the report_names_system iterates over the Player component of every entity that contains it:

fn report_names_system(query: Query<&Player>) {
    for player in &query {
        println!("Say hello to {}!", player.name);
    }
}

See also

iter_mut for mutable query items.

pub fn iter_mut(&mut self) -> QueryIter<'_, 's, D, F>

Returns an Iterator over the query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Example

Here, the gravity_system updates the Velocity component of every entity that contains it:

fn gravity_system(mut query: Query<&mut Velocity>) {
    const DELTA: f32 = 1.0 / 60.0;
    for mut velocity in &mut query {
        velocity.y -= 9.8 * DELTA;
    }
}

See also

iter for read-only query items.

pub fn iter_combinations<const K: usize>( &self, ) -> QueryCombinationIter<'_, 's, D::ReadOnly, F, K>

Returns a QueryCombinationIter over all combinations of K read-only query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Example

fn some_system(query: Query<&ComponentA>) {
    for [a1, a2] in query.iter_combinations() {
        // ...
    }
}

See also

• iter_combinations_mut for mutable query item combinations.

pub fn iter_combinations_mut<const K: usize>( &mut self, ) -> QueryCombinationIter<'_, 's, D, F, K>

Returns a QueryCombinationIter over all combinations of K query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Example

fn some_system(mut query: Query<&mut ComponentA>) {
    let mut combinations = query.iter_combinations_mut();
    while let Some([mut a1, mut a2]) = combinations.fetch_next() {
        // mutably access components data
    }
}

See also

• iter_combinations for read-only query item combinations.

pub fn iter_many<EntityList: IntoIterator<Item: Borrow<Entity>>>( &self, entities: EntityList, ) -> QueryManyIter<'_, 's, D::ReadOnly, F, EntityList::IntoIter>

Returns an Iterator over the read-only query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Example

// A component containing an entity list.
#[derive(Component)]
struct Friends {
    list: Vec<Entity>,
}

fn system(
    friends_query: Query<&Friends>,
    counter_query: Query<&Counter>,
) {
    for friends in &friends_query {
        for counter in counter_query.iter_many(&friends.list) {
            println!("Friend's counter: {:?}", counter.value);
        }
    }
}

See also

• iter_many_mut to get mutable query items.

pub fn iter_many_mut<EntityList: IntoIterator<Item: Borrow<Entity>>>( &mut self, entities: EntityList, ) -> QueryManyIter<'_, 's, D, F, EntityList::IntoIter>

Returns an iterator over the query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesnn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Examples

#[derive(Component)]
struct Counter {
    value: i32
}

#[derive(Component)]
struct Friends {
    list: Vec<Entity>,
}

fn system(
    friends_query: Query<&Friends>,
    mut counter_query: Query<&mut Counter>,
) {
    for friends in &friends_query {
        let mut iter = counter_query.iter_many_mut(&friends.list);
        while let Some(mut counter) = iter.fetch_next() {
            println!("Friend's counter: {:?}", counter.value);
            counter.value += 1;
        }
    }
}

pub unsafe fn iter_unsafe(&self) -> QueryIter<'_, 's, D, F>

Returns an Iterator over the query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Safety

This function makes it possible to violate Rust’s aliasing guarantees. You must make sure this call does not result in multiple mutable references to the same component.

See also

• iter and iter_mut for the safe versions.

pub unsafe fn iter_combinations_unsafe<const K: usize>( &self, ) -> QueryCombinationIter<'_, 's, D, F, K>

Iterates over all possible combinations of K query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Safety

This allows aliased mutability. You must make sure this call does not result in multiple mutable references to the same component.

See also

• iter_combinations and iter_combinations_mut for the safe versions.

pub unsafe fn iter_many_unsafe<EntityList: IntoIterator<Item: Borrow<Entity>>>( &self, entities: EntityList, ) -> QueryManyIter<'_, 's, D, F, EntityList::IntoIter>

Returns an Iterator over the query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesnn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Safety

This allows aliased mutability and does not check for entity uniqueness. You must make sure this call does not result in multiple mutable references to the same component. Particular care must be taken when collecting the data (rather than iterating over it one item at a time) such as via Iterator::collect.

See also

• iter_many_mut to safely access the query items.

pub fn par_iter(&self) -> QueryParIter<'_, '_, D::ReadOnly, F>

Returns a parallel iterator over the query results for the given World.

This parallel iterator is always guaranteed to return results from each matching entity once and only once. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryIter.

This can only be called for read-only queries, see par_iter_mut for write-queries.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn par_iter_mut(&mut self) -> QueryParIter<'_, '_, D, F>

Returns a parallel iterator over the query results for the given World.

This parallel iterator is always guaranteed to return results from each matching entity once and only once. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryIter.

This can only be called for mutable queries, see par_iter for read-only-queries.

Example

Here, the gravity_system updates the Velocity component of every entity that contains it:

fn gravity_system(mut query: Query<&mut Velocity>) {
    const DELTA: f32 = 1.0 / 60.0;
    query.par_iter_mut().for_each(|mut velocity| {
        velocity.y -= 9.8 * DELTA;
    });
}

pub fn get( &self, entity: Entity, ) -> Result<ROQueryItem<'_, D>, QueryEntityError<'_>>

Returns the read-only query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Example

Here, get is used to retrieve the exact query item of the entity specified by the SelectedCharacter resource.

fn print_selected_character_name_system(
       query: Query<&Character>,
       selection: Res<SelectedCharacter>
)
{
    if let Ok(selected_character) = query.get(selection.entity) {
        println!("{}", selected_character.name);
    }
}

See also

• get_mut to get a mutable query item.

pub fn get_many<const N: usize>( &self, entities: [Entity; N], ) -> Result<[ROQueryItem<'_, D>; N], QueryEntityError<'_>>

Returns the read-only query items for the given array of Entity.

The returned query items are in the same order as the input. In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead. The elements of the array do not need to be unique, unlike get_many_mut.

See also

• get_many_mut to get mutable query items.
• many for the panicking version.

pub fn many<const N: usize>( &self, entities: [Entity; N], ) -> [ROQueryItem<'_, D>; N]

Returns the read-only query items for the given array of Entity.

Panics

This method panics if there is a query mismatch or a non-existing entity.

Examples

use bevy_ecs::prelude::*;

#[derive(Component)]
struct Targets([Entity; 3]);

#[derive(Component)]
struct Position{
    x: i8,
    y: i8
};

impl Position {
    fn distance(&self, other: &Position) -> i8 {
        // Manhattan distance is way easier to compute!
        (self.x - other.x).abs() + (self.y - other.y).abs()
    }
}

fn check_all_targets_in_range(targeting_query: Query<(Entity, &Targets, &Position)>, targets_query: Query<&Position>){
    for (targeting_entity, targets, origin) in &targeting_query {
        // We can use "destructuring" to unpack the results nicely
        let [target_1, target_2, target_3] = targets_query.many(targets.0);

        assert!(target_1.distance(origin) <= 5);
        assert!(target_2.distance(origin) <= 5);
        assert!(target_3.distance(origin) <= 5);
    }
}

See also

• get_many for the non-panicking version.

pub fn get_mut( &mut self, entity: Entity, ) -> Result<D::Item<'_>, QueryEntityError<'_>>

Returns the query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Example

Here, get_mut is used to retrieve the exact query item of the entity specified by the PoisonedCharacter resource.

fn poison_system(mut query: Query<&mut Health>, poisoned: Res<PoisonedCharacter>) {
    if let Ok(mut health) = query.get_mut(poisoned.character_id) {
        health.0 -= 1;
    }
}

See also

• get to get a read-only query item.

pub fn get_many_mut<const N: usize>( &mut self, entities: [Entity; N], ) -> Result<[D::Item<'_>; N], QueryEntityError<'_>>

Returns the query items for the given array of Entity.

The returned query items are in the same order as the input. In case of a nonexisting entity, duplicate entities or mismatched component, a QueryEntityError is returned instead.

See also

• get_many to get read-only query items.
• many_mut for the panicking version.

pub fn many_mut<const N: usize>( &mut self, entities: [Entity; N], ) -> [D::Item<'_>; N]

Returns the query items for the given array of Entity.

Panics

This method panics if there is a query mismatch, a non-existing entity, or the same Entity is included more than once in the array.

Examples

use bevy_ecs::prelude::*;

#[derive(Component)]
struct Spring{
    connected_entities: [Entity; 2],
    strength: f32,
}

#[derive(Component)]
struct Position {
    x: f32,
    y: f32,
}

#[derive(Component)]
struct Force {
    x: f32,
    y: f32,
}

fn spring_forces(spring_query: Query<&Spring>, mut mass_query: Query<(&Position, &mut Force)>){
    for spring in &spring_query {
         // We can use "destructuring" to unpack our query items nicely
         let [(position_1, mut force_1), (position_2, mut force_2)] = mass_query.many_mut(spring.connected_entities);

         force_1.x += spring.strength * (position_1.x - position_2.x);
         force_1.y += spring.strength * (position_1.y - position_2.y);

         // Silence borrow-checker: I have split your mutable borrow!
         force_2.x += spring.strength * (position_2.x - position_1.x);
         force_2.y += spring.strength * (position_2.y - position_1.y);
    }
}

See also

• get_many_mut for the non panicking version.
• many to get read-only query items.

pub unsafe fn get_unchecked( &self, entity: Entity, ) -> Result<D::Item<'_>, QueryEntityError<'_>>

Returns the query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Safety

This function makes it possible to violate Rust’s aliasing guarantees. You must make sure this call does not result in multiple mutable references to the same component.

See also

• get_mut for the safe version.

pub fn single(&self) -> ROQueryItem<'_, D>

Returns a single read-only query item when there is exactly one entity matching the query.

Panics

This method panics if the number of query items is not exactly one.

Example

fn player_system(query: Query<&Position, With<Player>>) {
    let player_position = query.single();
    // do something with player_position
}

See also

• get_single for the non-panicking version.
• single_mut to get the mutable query item.

pub fn get_single(&self) -> Result<ROQueryItem<'_, D>, QuerySingleError>

Returns a single read-only query item when there is exactly one entity matching the query.

If the number of query items is not exactly one, a QuerySingleError is returned instead.

Example

fn player_scoring_system(query: Query<&PlayerScore>) {
    match query.get_single() {
        Ok(PlayerScore(score)) => {
            println!("Score: {}", score);
        }
        Err(QuerySingleError::NoEntities(_)) => {
            println!("Error: There is no player!");
        }
        Err(QuerySingleError::MultipleEntities(_)) => {
            println!("Error: There is more than one player!");
        }
    }
}

See also

• get_single_mut to get the mutable query item.
• single for the panicking version.

pub fn single_mut(&mut self) -> D::Item<'_>

Returns a single query item when there is exactly one entity matching the query.

Panics

This method panics if the number of query items is not exactly one.

Example

fn regenerate_player_health_system(mut query: Query<&mut Health, With<Player>>) {
    let mut health = query.single_mut();
    health.0 += 1;
}

See also

• get_single_mut for the non-panicking version.
• single to get the read-only query item.

pub fn get_single_mut(&mut self) -> Result<D::Item<'_>, QuerySingleError>

Returns a single query item when there is exactly one entity matching the query.

If the number of query items is not exactly one, a QuerySingleError is returned instead.

Example

fn regenerate_player_health_system(mut query: Query<&mut Health, With<Player>>) {
    let mut health = query.get_single_mut().expect("Error: Could not find a single player.");
    health.0 += 1;
}

See also

• get_single to get the read-only query item.
• single_mut for the panicking version.

pub fn is_empty(&self) -> bool

Returns true if there are no query items.

This is equivalent to self.iter().next().is_none(), and thus the worst case runtime will be O(n) where n is the number of potential matches. This can be notably expensive for queries that rely on non-archetypal filters such as Added or Changed which must individually check each query result for a match.

Example

Here, the score is increased only if an entity with a Player component is present in the world:

fn update_score_system(query: Query<(), With<Player>>, mut score: ResMut<Score>) {
    if !query.is_empty() {
        score.0 += 1;
    }
}

pub fn contains(&self, entity: Entity) -> bool

Returns true if the given Entity matches the query.

This is always guaranteed to run in O(1) time.

Example

fn targeting_system(in_range_query: Query<&InRange>, target: Res<Target>) {
    if in_range_query.contains(target.entity) {
        println!("Bam!")
    }
}

pub fn transmute_lens<NewD: QueryData>(&mut self) -> QueryLens<'_, NewD>

Returns a QueryLens that can be used to get a query with a more general fetch.

For example, this can transform a Query<(&A, &mut B)> to a Query<&B>. This can be useful for passing the query to another function. Note that since filter terms are dropped, non-archetypal filters like Added and Changed will not be respected. To maintain or change filter terms see Self::transmute_lens_filtered

Panics

This will panic if NewD is not a subset of the original fetch Q

Example

fn reusable_function(lens: &mut QueryLens<&A>) {
    assert_eq!(lens.query().single().0, 10);
}

// We can use the function in a system that takes the exact query.
fn system_1(mut query: Query<&A>) {
    reusable_function(&mut query.as_query_lens());
}

// We can also use it with a query that does not match exactly
// by transmuting it.
fn system_2(mut query: Query<(&mut A, &B)>) {
    let mut lens = query.transmute_lens::<&A>();
    reusable_function(&mut lens);
}

Allowed Transmutes

Besides removing parameters from the query, you can also make limited changes to the types of parameters.

• Can always add/remove Entity
• Can always add/remove EntityLocation
• Can always add/remove &Archetype
• Ref<T> <-> &T
• &mut T -> &T
• &mut T -> Ref<T>
• EntityMut -> EntityRef

pub fn transmute_lens_filtered<NewD: QueryData, NewF: QueryFilter>( &mut self, ) -> QueryLens<'_, NewD, NewF>

Equivalent to Self::transmute_lens but also includes a QueryFilter type.

Note that the lens will iterate the same tables and archetypes as the original query. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added and Changed will only be respected if they are in the type signature.

pub fn as_query_lens(&mut self) -> QueryLens<'_, D>

Gets a QueryLens with the same accesses as the existing query

pub fn join<OtherD: QueryData, NewD: QueryData>( &mut self, other: &mut Query<'_, '_, OtherD>, ) -> QueryLens<'_, NewD>

Returns a QueryLens that can be used to get a query with the combined fetch.

For example, this can take a Query<&A> and a Query<&B> and return a Query<(&A, &B)>. The returned query will only return items with both A and B. Note that since filters are dropped, non-archetypal filters like Added and Changed will not be respected. To maintain or change filter terms see Self::join_filtered.

Example

fn system(
    mut transforms: Query<&Transform>,
    mut players: Query<&Player>,
    mut enemies: Query<&Enemy>
) {
    let mut players_transforms: QueryLens<(&Transform, &Player)> = transforms.join(&mut players);
    for (transform, player) in &players_transforms.query() {
        // do something with a and b
    }

    let mut enemies_transforms: QueryLens<(&Transform, &Enemy)> = transforms.join(&mut enemies);
    for (transform, enemy) in &enemies_transforms.query() {
        // do something with a and b
    }
}

Panics

This will panic if NewD is not a subset of the union of the original fetch Q and OtherD.

Allowed Transmutes

Like transmute_lens the query terms can be changed with some restrictions. See Self::transmute_lens for more details.

pub fn join_filtered<OtherD: QueryData, OtherF: QueryFilter, NewD: QueryData, NewF: QueryFilter>( &mut self, other: &mut Query<'_, '_, OtherD, OtherF>, ) -> QueryLens<'_, NewD, NewF>

Equivalent to Self::join but also includes a QueryFilter type.

Note that the lens with iterate a subset of the original queries’ tables and archetypes. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added and Changed will only be respected if they are in the type signature.

pub fn get_inner( &self, entity: Entity, ) -> Result<ROQueryItem<'w, D>, QueryEntityError<'_>>

Returns the query item for the given Entity, with the actual “inner” world lifetime.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This can only return immutable data (mutable data will be cast to an immutable form). See get_mut for queries that contain at least one mutable component.

Example

Here, get is used to retrieve the exact query item of the entity specified by the SelectedCharacter resource.

fn print_selected_character_name_system(
       query: Query<&Character>,
       selection: Res<SelectedCharacter>
)
{
    if let Ok(selected_character) = query.get(selection.entity) {
        println!("{}", selected_character.name);
    }
}

pub fn iter_inner(&self) -> QueryIter<'w, 's, D::ReadOnly, F>

Returns an Iterator over the query items, with the actual “inner” world lifetime.

This can only return immutable data (mutable data will be cast to an immutable form). See Self::iter_mut for queries that contain at least one mutable component.

Example

Here, the report_names_system iterates over the Player component of every entity that contains it:

fn report_names_system(query: Query<&Player>) {
    for player in &query {
        println!("Say hello to {}!", player.name);
    }
}

Trait Implementations

impl<'w, 's, D: QueryData, F: QueryFilter> Deref for Populated<'w, 's, D, F>

type Target = Query<'w, 's, D, F>

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<D: QueryData, F: QueryFilter> DerefMut for Populated<'_, '_, D, F>

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.

impl<D: QueryData + 'static, F: QueryFilter + 'static> SystemParam for Populated<'_, '_, D, F>

type State = QueryState<D, F>

Used to store data which persists across invocations of a system.

type Item<'w, 's> = Populated<'w, 's, D, F>

The item type returned when constructing this system param. The value of this associated type should be Self, instantiated with new lifetimes.

fn init_state(world: &mut World, system_meta: &mut SystemMeta) -> Self::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

unsafe fn new_archetype( state: &mut Self::State, archetype: &Archetype, system_meta: &mut SystemMeta, )

For the specified Archetype, registers the components accessed by this SystemParam (if applicable).a

unsafe fn get_param<'w, 's>( state: &'s mut Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick, ) -> Self::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction.

unsafe fn validate_param( state: &Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'_>, ) -> bool

Validates that the param can be acquired by the get_param. Built-in executors use this to prevent systems with invalid params from running. For nested SystemParams validation will fail if any delegated validation fails.

fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)

Applies any deferred mutations stored in this SystemParam’s state. This is used to apply Commands during apply_deferred.

fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )

Queues any deferred mutations to be applied at the next apply_deferred.

impl<'w, 's, D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static> ReadOnlySystemParam for Populated<'w, 's, D, F>