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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
//! The `Castable` trait.
use std::mem;
use crate::conversions::{DerivedFrom, IDLInterface};
use crate::reflector::DomObject;
use crate::script_runtime::runtime_is_alive;
/// A trait to hold the cast functions of IDL interfaces that either derive
/// or are derived from other interfaces.
pub trait Castable: IDLInterface + DomObject + Sized {
/// Check whether a DOM object implements one of its deriving interfaces.
fn is<T>(&self) -> bool
where
T: DerivedFrom<Self>,
{
// This is a weird place for this check to live, but it should catch any
// attempts to interact with DOM objects from Drop implementations that run
// as a result of the runtime shutting down and finalizing all remaining objects.
debug_assert!(
runtime_is_alive(),
"Attempting to interact with DOM objects after JS runtime has shut down."
);
let id = self.reflector().proto_id();
id >= T::PROTO_FIRST && id <= T::PROTO_LAST
}
/// Cast a DOM object upwards to one of the interfaces it derives from.
fn upcast<T>(&self) -> &T
where
T: Castable,
Self: DerivedFrom<T>,
{
unsafe { mem::transmute::<&Self, &T>(self) }
}
/// Cast a DOM object downwards to one of the interfaces it might implement.
fn downcast<T>(&self) -> Option<&T>
where
T: DerivedFrom<Self>,
{
if self.is::<T>() {
Some(unsafe { mem::transmute::<&Self, &T>(self) })
} else {
None
}
}
}
#[expect(missing_docs)]
pub trait HasParent {
#[cfg_attr(crown, crown::unrooted_must_root_lint::must_root)]
type Parent;
fn as_parent(&self) -> &Self::Parent;
}