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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 http://mozilla.org/MPL/2.0/. */
//! The `Castable` trait.
pub use dom::bindings::codegen::InheritTypes::*;
use dom::bindings::conversions::{DerivedFrom, IDLInterface};
use dom::bindings::conversions::get_dom_class;
use dom::bindings::reflector::DomObject;
use std::mem;
/// 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>
{
let class = unsafe { get_dom_class(self.reflector().get_jsobject().get()).unwrap() };
T::derives(class)
}
/// 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) }
}
/// 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) })
} else {
None
}
}
}
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