| Quellcodebibliothek Statistik Leitseite products/Sources/formale Sprachen/C/Firefox/third_party/rust/objc2/src/ (Firefox Browser Version 153.0.1©) Datei vom 27.6.2026 mit Größe 1 kB |
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Quelle downcast.rsSprache: Rust |
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use crate::ClassType; /// Classes that can be safely downcasted to. /// /// [`DowncastTarget`] is an unsafe marker trait that can be implemented on /// types that also implement [`ClassType`]. /// /// Ideally, every type that implements `ClassType` would also be a valid /// downcast target, however this would be unsound when used with generics, /// because we can only trivially decide whether the "base container" is an /// instance of some class type, but anything related to the generic arguments /// is unknown. /// /// This trait is implemented automatically by the [`extern_class!`] and /// [`define_class!`] macros. /// /// [`extern_class!`]: crate::extern_class /// [`define_class!`]: crate::define_class /// /// /// # Safety /// /// The type must not have any generic arguments other than [`AnyObject`]. /// /// [`AnyObject`]: crate::runtime::AnyObject /// /// /// # Examples /// /// Implementing [`DowncastTarget`] for `NSString`: /// /// ```ignore /// // SAFETY: NSString does not have any generic parameters. /// unsafe impl DowncastTarget for NSString {} /// ``` /// /// However, implementing it for `NSArray` can only be done when the object /// type is `AnyObject`. /// /// ```ignore /// // SAFETY: NSArray does not have any generic parameters set (the generic /// // defaults to `AnyObject`). /// unsafe impl DowncastTarget for NSArray {} /// /// // This would not be valid, since downcasting can only trivially determine /// // whether the base class (in this case `NSArray`) matches the receiver /// // class type. /// // unsafe impl<T: Message> DowncastTarget for NSArray<T> {} /// ``` pub unsafe trait DowncastTarget: ClassType + 'static {}
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2026-08-25