use core::fmt;
-use core::any::Any;
+use core::any::{Any, TypeId};
+#[cfg(not(feature = "std"))]
+use alloc::boxed::Box;
#[doc(hidden)]
pub trait CloneToAny {
}
}
-#[allow(missing_docs)] // Bogus warning (it’s not public outside the crate), ☹
-pub trait UncheckedAnyExt: Any {
- unsafe fn downcast_ref_unchecked<T: Any>(&self) -> &T;
- unsafe fn downcast_mut_unchecked<T: Any>(&mut self) -> &mut T;
- unsafe fn downcast_unchecked<T: Any>(self: Box<Self>) -> Box<T>;
+/// Methods for downcasting from an `Any`-like trait object.
+///
+/// This should only be implemented on trait objects for subtraits of `Any`, though you can
+/// implement it for other types and it’ll work fine, so long as your implementation is correct.
+pub trait Downcast {
+ /// Gets the `TypeId` of `self`.
+ fn type_id(&self) -> TypeId;
+
+ // Note the bound through these downcast methods is 'static, rather than the inexpressible
+ // concept of Self-but-as-a-trait (where Self is `dyn Trait`). This is sufficient, exceeding
+ // TypeId’s requirements. Sure, you *can* do CloneAny.downcast_unchecked::<NotClone>() and the
+ // type system won’t protect you, but that doesn’t introduce any unsafety: the method is
+ // already unsafe because you can specify the wrong type, and if this were exposing safe
+ // downcasting, CloneAny.downcast::<NotClone>() would just return an error, which is just as
+ // correct.
+ //
+ // Now in theory we could also add T: ?Sized, but that doesn’t play nicely with the common
+ // implementation, so I’m doing without it.
+
+ /// Downcast from `&Any` to `&T`, without checking the type matches.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `T` matches the trait object, on pain of *undefined behaviour*.
+ unsafe fn downcast_ref_unchecked<T: 'static>(&self) -> &T;
+
+ /// Downcast from `&mut Any` to `&mut T`, without checking the type matches.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `T` matches the trait object, on pain of *undefined behaviour*.
+ unsafe fn downcast_mut_unchecked<T: 'static>(&mut self) -> &mut T;
+
+ /// Downcast from `Box<Any>` to `Box<T>`, without checking the type matches.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `T` matches the trait object, on pain of *undefined behaviour*.
+ unsafe fn downcast_unchecked<T: 'static>(self: Box<Self>) -> Box<T>;
}
-#[doc(hidden)]
/// A trait for the conversion of an object into a boxed trait object.
-pub trait IntoBox<A: ?Sized + UncheckedAnyExt>: Any {
+pub trait IntoBox<A: ?Sized + Downcast>: Any {
/// Convert self into the appropriate boxed form.
fn into_box(self) -> Box<A>;
}
macro_rules! implement {
- ($base:ident, $(+ $bounds:ident)*) => {
- impl UncheckedAnyExt for dyn $base $(+ $bounds)* {
+ ($any_trait:ident $(+ $auto_traits:ident)*) => {
+ impl Downcast for dyn $any_trait $(+ $auto_traits)* {
+ #[inline]
+ fn type_id(&self) -> TypeId {
+ self.type_id()
+ }
+
#[inline]
unsafe fn downcast_ref_unchecked<T: 'static>(&self) -> &T {
&*(self as *const Self as *const T)
}
}
- impl<T: $base $(+ $bounds)*> IntoBox<dyn $base $(+ $bounds)*> for T {
+ impl<T: $any_trait $(+ $auto_traits)*> IntoBox<dyn $any_trait $(+ $auto_traits)*> for T {
#[inline]
- fn into_box(self) -> Box<dyn $base $(+ $bounds)*> {
+ fn into_box(self) -> Box<dyn $any_trait $(+ $auto_traits)*> {
Box::new(self)
}
}
}
}
-implement!(Any,);
-implement!(Any, + Send);
-implement!(Any, + Send + Sync);
+implement!(Any);
+implement!(Any + Send);
+implement!(Any + Send + Sync);
/// [`Any`], but with cloning.
///
/// See [`core::any`] for more details on `Any` in general.
pub trait CloneAny: Any + CloneToAny { }
impl<T: Any + Clone> CloneAny for T { }
-implement!(CloneAny,);
-implement!(CloneAny, + Send);
-implement!(CloneAny, + Send + Sync);
+implement!(CloneAny);
+implement!(CloneAny + Send);
+implement!(CloneAny + Send + Sync);
impl_clone!(dyn CloneAny);
impl_clone!(dyn CloneAny + Send);
impl_clone!(dyn CloneAny + Send + Sync);