Trait VcValueTrait 

pub trait VcValueTrait:
    NonLocalValue
    + Send
    + Sync
    + 'static {
    type ValueTrait: ?Sized;

    // Required methods
    fn get_trait_type_id() -> TraitTypeId;
    fn get_impl_vtables() -> &'static VTableRegistry<Self::ValueTrait>;
}

A trait implemented on all values trait object references that can be used with a value cell (Vc<Box<dyn Trait>>).

You should not create subtraits of this trait manually, but instead use the #[turbo_tasks::value_trait] macro. Implementations of VcValueTraits should use the #[turbo_tasks::value_impl] macro.

Upcasting

A concrete Vc of a VcValueType can be converted to a Vc of a VcValueTrait with an upcast:

let something_vc: Vc<ConcreteType> = ...;
let trait_vc: Vc<Box<dyn MyTrait>> = Vc::upcast(something_vc);

// there is an equivalent API for ResolvedVc
let something_resolved_vc: ResolvedVc<ConcreteType> = ...;
let trait_resolved_vc: ResolvedVc<Box<dyn MyTrait>> = ResolvedVc::upcast(something_resolved_vc);

Upcast safety is enforced at compile-time with the Upcast and UpcastStrict traits. Upcasts always succeed.

Downcasting

A ResolvedVc containing a VcValueTrait subtrait can be downcast to a concrete type with ResolvedVc::try_downcast_type:

let trait_vc: Vc<Box<dyn MyTrait>> = ...;
if let Some(something_vc) = ResolvedVc::try_downcast_type::<Something>(trait_vc) {
    // ...
}

A supertrait can be cast to a subtrait with ResolvedVc::try_downcast:

let trait_vc: Vc<Box<dyn SubTrait>> = ...;
if let Some(something_vc) = ResolvedVc::try_downcast::<Box<dyn SuperTrait>>(trait_vc) {
    // ...
}

If you have an unresolved Vc that you’d like to downcast, you should resolve it first.

A compile-time check using the Upcast and UpcastStrict traits ensures that a downcast is possible (the target type or trait implements the source trait), but it may still return None at runtime if the concrete value does not implement the trait.

Sidecasting

In some cases, you may want to convert between two traits that do not have a supertrait/subtrait relationship:

let trait_vc: Vc<Box<dyn MyTrait>> = ...;
if let Some(something_vc) = ResolvedVc::try_sidecast::<Box<dyn UnrelatedTrait>>(trait_vc) {
    // ...
}

If you have an unresolved Vc that you’d like to sidecast, you should resolve it first.

This won’t do any compile-time checks, so downcasting should be preferred if possible. It will return None at runtime if the cast fails.

Reading

Trait object Vcs can be read by converting them to a TraitRef, which allows non-turbo-tasks functions defined on the trait to be called.

let trait_vc: Vc<Box<dyn MyTrait>> = ...;
let trait_ref: TraitRef<Box<dyn MyTrait>> = trait_vc.into_trait_ref().await?;

trait_ref.non_turbo_tasks_function();

Required Associated Types

type ValueTrait: ?Sized

Required Methods

fn get_trait_type_id() -> TraitTypeId

Returns the type id of the trait object.

fn get_impl_vtables() -> &'static VTableRegistry<Self::ValueTrait>

Returns the vtable for an implementation of this trait. Panics if ValueTypeId does not implement the trait.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl VcValueTrait for Box<dyn ValueDebug>

type ValueTrait = dyn ValueDebug

fn get_trait_type_id() -> TraitTypeId

fn get_impl_vtables() -> &'static VTableRegistry<Self::ValueTrait>

impl VcValueTrait for Box<dyn ValueToString>

type ValueTrait = dyn ValueToString

fn get_trait_type_id() -> TraitTypeId

fn get_impl_vtables() -> &'static VTableRegistry<Self::ValueTrait>

impl VcValueTrait for Box<dyn ValueDefault>

type ValueTrait = dyn ValueDefault

fn get_trait_type_id() -> TraitTypeId

fn get_impl_vtables() -> &'static VTableRegistry<Self::ValueTrait>

impl VcValueTrait for Box<dyn Effect>

type ValueTrait = dyn Effect

fn get_trait_type_id() -> TraitTypeId

fn get_impl_vtables() -> &'static VTableRegistry<Self::ValueTrait>

Implementors