Struct Mut 

pub struct Mut<'w, T>
where
    T: ?Sized,
{ /* private fields */ }

Unique mutable borrow of an entity’s component or of a resource.

This can be used in queries to opt into change detection on both their mutable and immutable forms, as opposed to &mut T, which only provides access to change detection while in its mutable form:

#[derive(Component, Clone)]
struct Name(String);

#[derive(Component, Clone, Copy)]
struct Health(f32);

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

#[derive(Component, Clone, Copy)]
struct Player {
    id: usize,
};

#[derive(QueryData)]
#[query_data(mutable)]
struct PlayerQuery {
    id: &'static Player,

    // Reacting to `PlayerName` changes is expensive, so we need to enable change detection when reading it.
    name: Mut<'static, Name>,

    health: &'static mut Health,
    position: &'static mut Position,
}

fn update_player_avatars(players_query: Query<PlayerQuery>) {
    // The item returned by the iterator is of type `PlayerQueryReadOnlyItem`.
    for player in players_query.iter() {
        if player.name.is_changed() {
            // Update the player's name. This clones a String, and so is more expensive.
            update_player_name(player.id, player.name.clone());
        }

        // Update the health bar.
        update_player_health(player.id, *player.health);

        // Update the player's position.
        update_player_position(player.id, *player.position);
    }
}

Implementations

impl<'w, T> Mut<'w, T>

where T: ?Sized,

pub fn new( value: &'w mut T, added: &'w mut Tick, last_changed: &'w mut Tick, last_run: Tick, this_run: Tick, caller: MaybeLocation<&'w mut &'static Location<'static>>, ) -> Mut<'w, T>

Creates a new change-detection enabled smart pointer. In almost all cases you do not need to call this method manually, as instances of Mut will be created by engine-internal code.

Many use-cases of this method would be better served by Mut::map_unchanged or Mut::reborrow.

• value - The value wrapped by this smart pointer.
• added - A Tick that stores the tick when the wrapped value was created.
• last_changed - A Tick that stores the last time the wrapped value was changed. This will be updated to the value of change_tick if the returned smart pointer is modified.
• last_run - A Tick, occurring before this_run, which is used as a reference to determine whether the wrapped value is newly added or changed.
• this_run - A Tick corresponding to the current point in time – “now”.

pub fn set_ticks(&mut self, last_run: Tick, this_run: Tick)

Overwrite the last_run and this_run tick that are used for change detection.

This is an advanced feature. Muts are usually created by engine-internal code and consumed by end-user code.

impl<'w, T> Mut<'w, T>

where T: ?Sized,

pub fn into_inner(self) -> &'w mut T

Consume self and return a mutable reference to the contained value while marking self as “changed”.

pub fn reborrow(&mut self) -> Mut<'_, T>

Returns a Mut<> with a smaller lifetime. This is useful if you have &mut Mut <T>, but you need a Mut<T>.

pub fn map_unchanged<U>(self, f: impl FnOnce(&mut T) -> &mut U) -> Mut<'w, U>

where U: ?Sized,

Maps to an inner value by applying a function to the contained reference, without flagging a change.

You should never modify the argument passed to the closure – if you want to modify the data without flagging a change, consider using DetectChangesMut::bypass_change_detection to make your intent explicit.

// When run, zeroes the translation of every entity.
fn reset_positions(mut transforms: Query<&mut Transform>) {
    for transform in &mut transforms {
        // We pinky promise not to modify `t` within the closure.
        // Breaking this promise will result in logic errors, but will never cause undefined behavior.
        let mut translation = transform.map_unchanged(|t| &mut t.translation);
        // Only reset the translation if it isn't already zero;
        translation.set_if_neq(Vec2::ZERO);
    }
}

pub fn filter_map_unchanged<U>( self, f: impl FnOnce(&mut T) -> Option<&mut U>, ) -> Option<Mut<'w, U>>

where U: ?Sized,

Optionally maps to an inner value by applying a function to the contained reference. This is useful in a situation where you need to convert a Mut<T> to a Mut<U>, but only if T contains U.

As with map_unchanged, you should never modify the argument passed to the closure.

pub fn try_map_unchanged<U, E>( self, f: impl FnOnce(&mut T) -> Result<&mut U, E>, ) -> Result<Mut<'w, U>, E>

where U: ?Sized,

Optionally maps to an inner value by applying a function to the contained reference, returns an error on failure. This is useful in a situation where you need to convert a Mut<T> to a Mut<U>, but only if T contains U.

As with map_unchanged, you should never modify the argument passed to the closure.

pub fn as_deref_mut(&mut self) -> Mut<'_, <T as Deref>::Target>

where T: DerefMut,

Allows you access to the dereferenced value of this pointer without immediately triggering change detection.

Trait Implementations

impl<'w, T> AsMut<T> for Mut<'w, T>

fn as_mut(&mut self) -> &mut T

Converts this type into a mutable reference of the (usually inferred) input type.

impl<'w, T> AsRef<T> for Mut<'w, T>

fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.

impl<'w, T> Debug for Mut<'w, T>

where T: Debug + ?Sized,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'w, T> Deref for Mut<'w, T>

where T: ?Sized,

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &<Mut<'w, T> as Deref>::Target

Dereferences the value.

impl<'w, T> DerefMut for Mut<'w, T>

where T: ?Sized,

fn deref_mut(&mut self) -> &mut <Mut<'w, T> as Deref>::Target

Mutably dereferences the value.

impl<'w, T> DetectChanges for Mut<'w, T>

where T: ?Sized,

fn is_added(&self) -> bool

Returns true if this value was added after the system last ran.

fn is_changed(&self) -> bool

Returns true if this value was added or mutably dereferenced either since the last time the system ran or, if the system never ran, since the beginning of the program.

fn last_changed(&self) -> Tick

Returns the change tick recording the time this data was most recently changed.

fn added(&self) -> Tick

Returns the change tick recording the time this data was added.

fn changed_by(&self) -> MaybeLocation

The location that last caused this to change.

impl<'w, T> DetectChangesMut for Mut<'w, T>

where T: ?Sized,

type Inner = T

The type contained within this smart pointer

fn set_changed(&mut self)

Flags this value as having been changed.

fn set_added(&mut self)

Flags this value as having been added.

fn set_last_changed(&mut self, last_changed: Tick)

Manually sets the change tick recording the time when this data was last mutated.

fn set_last_added(&mut self, last_added: Tick)

Manually sets the added tick recording the time when this data was last added.

fn bypass_change_detection( &mut self, ) -> &mut <Mut<'w, T> as DetectChangesMut>::Inner

Manually bypasses change detection, allowing you to mutate the underlying value without updating the change tick.

fn set_if_neq(&mut self, value: Self::Inner) -> bool

where Self::Inner: Sized + PartialEq,

Overwrites this smart pointer with the given value, if and only if *self != value. Returns true if the value was overwritten, and returns false if it was not.

fn replace_if_neq(&mut self, value: Self::Inner) -> Option<Self::Inner>

where Self::Inner: Sized + PartialEq,

Overwrites this smart pointer with the given value, if and only if *self != value, returning the previous value if this occurs.

fn clone_from_if_neq<T>(&mut self, value: &T) -> bool

where T: ToOwned<Owned = Self::Inner> + ?Sized, Self::Inner: PartialEq<T>,

Overwrites this smart pointer with a clone of the given value, if and only if *self != value. Returns true if the value was overwritten, and returns false if it was not.

impl<'w, T> From<Mut<'w, T>> for Ref<'w, T>

where T: ?Sized,

fn from(mut_ref: Mut<'w, T>) -> Ref<'w, T>

Converts to this type from the input type.

impl<'w, T> From<NonSendMut<'w, T>> for Mut<'w, T>

where T: 'static,

fn from(other: NonSendMut<'w, T>) -> Mut<'w, T>

Convert this NonSendMut into a Mut. This allows keeping the change-detection feature of Mut while losing the specificity of NonSendMut.

impl<'w, T> From<ResMut<'w, T>> for Mut<'w, T>

where T: Resource,

fn from(other: ResMut<'w, T>) -> Mut<'w, T>

Convert this ResMut into a Mut. This allows keeping the change-detection feature of Mut while losing the specificity of ResMut for resources.

impl<'w, 'a, T> IntoIterator for &'a Mut<'w, T>

where &'a T: IntoIterator,

type Item = <&'a T as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <&'a T as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter(self) -> <&'a Mut<'w, T> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'w, 'a, T> IntoIterator for &'a mut Mut<'w, T>

where &'a mut T: IntoIterator,

type Item = <&'a mut T as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <&'a mut T as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter(self) -> <&'a mut Mut<'w, T> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'__w, T> QueryData for Mut<'__w, T>

where T: Component<Mutability = Mutable>,

const IS_READ_ONLY: bool = false

True if this query is read-only and may not perform mutable access.

type ReadOnly = Ref<'__w, T>

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

type Item<'w> = Mut<'w, T>

The item returned by this WorldQuery This will be the data retrieved by the query, and is visible to the end user when calling e.g. Query<Self>::get.

fn shrink<'wlong, 'wshort>(item: Mut<'wlong, T>) -> Mut<'wshort, T>

where 'wlong: 'wshort,

This function manually implements subtyping for the query items.

unsafe fn fetch<'w>( fetch: &mut <Mut<'__w, T> as WorldQuery>::Fetch<'w>, entity: Entity, table_row: TableRow, ) -> Mut<'w, T>

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 an entity in the current archetype. Accesses components registered in WorldQuery::update_component_access.

impl<'__w, T> WorldQuery for Mut<'__w, T>

where T: Component,

When Mut<T> is used in a query, it will be converted to Ref<T> when transformed into its read-only form, providing access to change detection methods.

By contrast &mut T will result in a Mut<T> item in mutable form to record mutations, but result in a bare &T in read-only form.

SAFETY: fetch accesses a single component mutably. This is sound because update_component_access and update_archetype_component_access add write access for that component and panic when appropriate. update_component_access adds a With filter for a component. This is sound because matches_component_set returns whether the set contains that component.

const IS_DENSE: bool = <&mut T as WorldQuery>::IS_DENSE

Returns true if (and only if) every table of every archetype matched by this fetch contains all of the matched components.

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

Per archetype/table state retrieved by this WorldQuery to compute Self::Item for each entity.

type State = ComponentId

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_fetch<'wlong, 'wshort>( fetch: <Mut<'__w, T> as WorldQuery>::Fetch<'wlong>, ) -> <Mut<'__w, T> as WorldQuery>::Fetch<'wshort>

where 'wlong: 'wshort,

This function manually implements subtyping for the query fetches.

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

Creates a new instance of Self::Fetch, by combining data from the World with the cached Self::State. Readonly accesses resources registered in WorldQuery::update_component_access.

unsafe fn set_archetype<'w>( fetch: &mut WriteFetch<'w, T>, state: &ComponentId, 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 WriteFetch<'w, T>, state: &ComponentId, table: &'w Table, )

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

fn update_component_access( _: &ComponentId, access: &mut FilteredAccess<ComponentId>, )

Adds any component accesses used by this WorldQuery to access.

fn init_state(world: &mut World) -> ComponentId

Creates and initializes a State for this WorldQuery type.

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

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

fn matches_component_set( state: &ComponentId, 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.