Struct If 

pub struct If<T>(pub T);

A SystemParam that wraps another parameter and causes its system to skip instead of failing when the parameter is invalid.

Example

// This system will fail if `SomeResource` is not present.
fn fails_on_missing_resource(res: Res<SomeResource>) {}

// This system will skip without error if `SomeResource` is not present.
fn skips_on_missing_resource(res: If<Res<SomeResource>>) {
    // The inner parameter is available using `Deref`
    let some_resource: &SomeResource = &res;
}

Tuple Fields

0: T

Implementations

impl<T> If<T>

pub fn into_inner(self) -> T

Returns the inner T.

The inner value is pub, so you can also obtain it by destructuring the parameter:

fn skips_on_missing_resource(If(res): If<Res<SomeResource>>) {
    let some_resource: Res<SomeResource> = res;
}

Trait Implementations

impl<T: Debug> Debug for If<T>

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

Formats the value using the given formatter.

impl<T> Deref for If<T>

type Target = T

The resulting type after dereferencing.

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

Dereferences the value.

impl<T> DerefMut for If<T>

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

Mutably dereferences the value.

impl<T: SystemParam> SystemParam for If<T>

type State = <T as SystemParam>::State

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

type Item<'world, 'state> = If<<T as SystemParam>::Item<'world, 'state>>

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) -> Self::State

Creates a new instance of this param’s State.

fn init_access( state: &Self::State, system_meta: &mut SystemMeta, component_access_set: &mut FilteredAccessSet, world: &mut World, )

Registers any World access used by this SystemParam

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

Validates that the param can be acquired by the get_param.

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

Creates a parameter to be passed into a SystemParamFunction.

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 ApplyDeferred.

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

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

impl<P: SystemParam, B: SystemParamBuilder<P>> SystemParamBuilder<If<P>> for IfBuilder<B>

fn build(self, world: &mut World) -> <If<P> as SystemParam>::State

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

fn build_state(self, world: &mut World) -> SystemState<P>

Create a SystemState from a SystemParamBuilder. To create a system, call SystemState::build_system on the result.

impl<T: ReadOnlySystemParam> ReadOnlySystemParam for If<T>