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use std::{fmt::Debug, future::Future, marker::PhantomData};
use anyhow::Result;
use serde::{Deserialize, Serialize};
use crate::{
Vc, VcValueTrait,
registry::get_value_type,
task::shared_reference::TypedSharedReference,
vc::{ReadVcFuture, VcValueTraitCast, cast::VcCast},
};
/// Similar to a [`ReadRef<T>`][crate::ReadRef], but contains a value trait
/// object instead.
///
/// The only way to interact with a `TraitRef<T>` is by passing
/// it around or turning it back into a value trait vc by calling
/// [`ReadRef::cell`][crate::ReadRef::cell].
///
/// Internally it stores a reference counted reference to a value on the heap.
pub struct TraitRef<T>
where
T: ?Sized,
{
shared_reference: TypedSharedReference,
_t: PhantomData<T>,
}
impl<T> Debug for TraitRef<T> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("TraitRef")
.field("shared_reference", &self.shared_reference)
.finish()
}
}
impl<T> Clone for TraitRef<T> {
fn clone(&self) -> Self {
Self {
shared_reference: self.shared_reference.clone(),
_t: PhantomData,
}
}
}
impl<T> PartialEq for TraitRef<T> {
fn eq(&self, other: &Self) -> bool {
self.shared_reference == other.shared_reference
}
}
impl<T> Eq for TraitRef<T> {}
impl<T> std::hash::Hash for TraitRef<T> {
fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
self.shared_reference.hash(state)
}
}
impl<T> Serialize for TraitRef<T> {
fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
self.shared_reference.serialize(serializer)
}
}
impl<'de, T> Deserialize<'de> for TraitRef<T> {
fn deserialize<D: serde::Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
Ok(Self {
shared_reference: TypedSharedReference::deserialize(deserializer)?,
_t: PhantomData,
})
}
}
// This is a workaround for https://github.com/rust-lang/rust-analyzer/issues/19971
// that ensures type inference keeps working with ptr_metadata.
#[cfg(rust_analyzer)]
impl<U> std::ops::Deref for TraitRef<Box<U>>
where
U: ?Sized,
Box<U>: VcValueTrait,
{
type Target = U;
fn deref(&self) -> &Self::Target {
unimplemented!("only exists for rust-analyzer type inference")
}
}
#[cfg(not(rust_analyzer))]
impl<U> std::ops::Deref for TraitRef<Box<U>>
where
Box<U>: VcValueTrait<ValueTrait = U>,
U: std::ptr::Pointee<Metadata = std::ptr::DynMetadata<U>> + ?Sized,
{
type Target = U;
fn deref(&self) -> &Self::Target {
// This lookup will fail if the value type stored does not actually implement the trait,
// which implies a bug in either the registry code or the macro code.
let metadata =
<Box<U> as VcValueTrait>::get_impl_vtables().get(self.shared_reference.type_id);
let downcast_ptr = std::ptr::from_raw_parts(
self.shared_reference.reference.0.as_ptr() as *const (),
metadata,
);
unsafe { &*downcast_ptr }
}
}
// Otherwise, TraitRef<Box<dyn Trait>> would not be Sync.
// SAFETY: TraitRef doesn't actually contain a T.
unsafe impl<T> Sync for TraitRef<T> where T: ?Sized {}
// Otherwise, TraitRef<Box<dyn Trait>> would not be Send.
// SAFETY: TraitRef doesn't actually contain a T.
unsafe impl<T> Send for TraitRef<T> where T: ?Sized {}
impl<T> Unpin for TraitRef<T> where T: ?Sized {}
impl<T> TraitRef<T>
where
T: ?Sized,
{
pub(crate) fn new(shared_reference: TypedSharedReference) -> Self {
Self {
shared_reference,
_t: PhantomData,
}
}
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
triomphe::Arc::ptr_eq(
&this.shared_reference.reference.0,
&other.shared_reference.reference.0,
)
}
}
impl<T> TraitRef<T>
where
T: VcValueTrait + ?Sized,
{
/// Returns a new cell that points to a value that implements the value
/// trait `T`.
pub fn cell(trait_ref: TraitRef<T>) -> Vc<T> {
let TraitRef {
shared_reference, ..
} = trait_ref;
let value_type = get_value_type(shared_reference.type_id);
(value_type.raw_cell)(shared_reference).into()
}
}
/// A trait that allows a value trait vc to be converted into a trait reference.
///
/// The signature is similar to `IntoFuture`, but we don't want trait vcs to
/// have the same future-like semantics as value vcs when it comes to producing
/// refs. This behavior is rarely needed, so in most cases, `.await`ing a trait
/// vc is a mistake.
pub trait IntoTraitRef {
type ValueTrait: VcValueTrait + ?Sized;
type Future: Future<Output = Result<<VcValueTraitCast<Self::ValueTrait> as VcCast>::Output>>;
fn into_trait_ref(self) -> Self::Future;
}
impl<T> IntoTraitRef for Vc<T>
where
T: VcValueTrait + ?Sized,
{
type ValueTrait = T;
type Future = ReadVcFuture<T, VcValueTraitCast<T>>;
fn into_trait_ref(self) -> Self::Future {
self.node.into_read().into()
}
}
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