#[cfg(test)]
use std::boxed::Box;
+use core::any::Any;
use core::borrow;
use core::cell::Cell;
use core::cmp::Ordering;
}
}
+impl Rc<Any> {
+ #[inline]
+ #[unstable(feature = "rc_downcast", issue = "0")]
+ /// Attempt to downcast the `Rc<Any>` to a concrete type.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// #![feature(rc_downcast)]
+ /// use std::any::Any;
+ /// use std::rc::Rc;
+ ///
+ /// fn print_if_string(value: Rc<Any>) {
+ /// if let Ok(string) = value.downcast::<String>() {
+ /// println!("String ({}): {}", string.len(), string);
+ /// }
+ /// }
+ ///
+ /// fn main() {
+ /// let my_string = "Hello World".to_string();
+ /// print_if_string(Rc::new(my_string));
+ /// print_if_string(Rc::new(0i8));
+ /// }
+ /// ```
+ pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<Any>> {
+ if (*self).is::<T>() {
+ // avoid the pointer arithmetic in from_raw
+ unsafe {
+ let raw: *const RcBox<Any> = self.ptr.as_ptr();
+ forget(self);
+ Ok(Rc {
+ ptr: Shared::new_unchecked(raw as *const RcBox<T> as *mut _),
+ })
+ }
+ } else {
+ Err(self)
+ }
+ }
+}
+
impl<T: ?Sized> Rc<T> {
// Allocates an `RcBox<T>` with sufficient space for an unsized value
unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> {
assert_eq!(&r[..], [1, 2, 3]);
}
+
+ #[test]
+ fn test_downcast() {
+ use std::any::Any;
+
+ let r1: Rc<Any> = Rc::new(i32::max_value());
+ let r2: Rc<Any> = Rc::new("abc");
+
+ assert!(r1.clone().downcast::<u32>().is_err());
+
+ let r1i32 = r1.downcast::<i32>();
+ assert!(r1i32.is_ok());
+ assert_eq!(r1i32.unwrap(), Rc::new(i32::max_value()));
+
+ assert!(r2.clone().downcast::<i32>().is_err());
+
+ let r2str = r2.downcast::<&'static str>();
+ assert!(r2str.is_ok());
+ assert_eq!(r2str.unwrap(), Rc::new("abc"));
+ }
}
#[stable(feature = "rust1", since = "1.0.0")]